Note that the examples for the structure copying bug example are no

[perl5.git] / sv.c

/*    sv.c
 *
 *    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
 *    2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, by Larry Wall and others
 *
 *    You may distribute under the terms of either the GNU General Public
 *    License or the Artistic License, as specified in the README file.
 *
 * "I wonder what the Entish is for 'yes' and 'no'," he thought.
 *
 *
 * This file contains the code that creates, manipulates and destroys
 * scalar values (SVs). The other types (AV, HV, GV, etc.) reuse the
 * structure of an SV, so their creation and destruction is handled
 * here; higher-level functions are in av.c, hv.c, and so on. Opcode
 * level functions (eg. substr, split, join) for each of the types are
 * in the pp*.c files.
 */

#include "EXTERN.h"
#define PERL_IN_SV_C
#include "perl.h"
#include "regcomp.h"

#define FCALL *f

#ifdef __Lynx__
/* Missing proto on LynxOS */
  char *gconvert(double, int, int,  char *);
#endif

#ifdef PERL_UTF8_CACHE_ASSERT
/* if adding more checks watch out for the following tests:
 *   t/op/index.t t/op/length.t t/op/pat.t t/op/substr.t
 *   lib/utf8.t lib/Unicode/Collate/t/index.t
 * --jhi
 */
#   define ASSERT_UTF8_CACHE(cache) \
    STMT_START { if (cache) { assert((cache)[0] <= (cache)[1]); \
                              assert((cache)[2] <= (cache)[3]); \
                              assert((cache)[3] <= (cache)[1]);} \
                              } STMT_END
#else
#   define ASSERT_UTF8_CACHE(cache) NOOP
#endif

#ifdef PERL_OLD_COPY_ON_WRITE
#define SV_COW_NEXT_SV(sv)      INT2PTR(SV *,SvUVX(sv))
#define SV_COW_NEXT_SV_SET(current,next)        SvUV_set(current, PTR2UV(next))
/* This is a pessimistic view. Scalar must be purely a read-write PV to copy-
   on-write.  */
#endif

/* ============================================================================

=head1 Allocation and deallocation of SVs.

An SV (or AV, HV, etc.) is allocated in two parts: the head (struct
sv, av, hv...) contains type and reference count information, and for
many types, a pointer to the body (struct xrv, xpv, xpviv...), which
contains fields specific to each type.  Some types store all they need
in the head, so don't have a body.

In all but the most memory-paranoid configuations (ex: PURIFY), heads
and bodies are allocated out of arenas, which by default are
approximately 4K chunks of memory parcelled up into N heads or bodies.
Sv-bodies are allocated by their sv-type, guaranteeing size
consistency needed to allocate safely from arrays.

For SV-heads, the first slot in each arena is reserved, and holds a
link to the next arena, some flags, and a note of the number of slots.
Snaked through each arena chain is a linked list of free items; when
this becomes empty, an extra arena is allocated and divided up into N
items which are threaded into the free list.

SV-bodies are similar, but they use arena-sets by default, which
separate the link and info from the arena itself, and reclaim the 1st
slot in the arena.  SV-bodies are further described later.

The following global variables are associated with arenas:

    PL_sv_arenaroot     pointer to list of SV arenas
    PL_sv_root          pointer to list of free SV structures

    PL_body_arenas      head of linked-list of body arenas
    PL_body_roots[]     array of pointers to list of free bodies of svtype
                        arrays are indexed by the svtype needed

A few special SV heads are not allocated from an arena, but are
instead directly created in the interpreter structure, eg PL_sv_undef.
The size of arenas can be changed from the default by setting
PERL_ARENA_SIZE appropriately at compile time.

The SV arena serves the secondary purpose of allowing still-live SVs
to be located and destroyed during final cleanup.

At the lowest level, the macros new_SV() and del_SV() grab and free
an SV head.  (If debugging with -DD, del_SV() calls the function S_del_sv()
to return the SV to the free list with error checking.) new_SV() calls
more_sv() / sv_add_arena() to add an extra arena if the free list is empty.
SVs in the free list have their SvTYPE field set to all ones.

At the time of very final cleanup, sv_free_arenas() is called from
perl_destruct() to physically free all the arenas allocated since the
start of the interpreter.

Manipulation of any of the PL_*root pointers is protected by enclosing
LOCK_SV_MUTEX; ... UNLOCK_SV_MUTEX calls which should Do the Right Thing
if threads are enabled.

The function visit() scans the SV arenas list, and calls a specified
function for each SV it finds which is still live - ie which has an SvTYPE
other than all 1's, and a non-zero SvREFCNT. visit() is used by the
following functions (specified as [function that calls visit()] / [function
called by visit() for each SV]):

    sv_report_used() / do_report_used()
                        dump all remaining SVs (debugging aid)

    sv_clean_objs() / do_clean_objs(),do_clean_named_objs()
                        Attempt to free all objects pointed to by RVs,
                        and, unless DISABLE_DESTRUCTOR_KLUDGE is defined,
                        try to do the same for all objects indirectly
                        referenced by typeglobs too.  Called once from
                        perl_destruct(), prior to calling sv_clean_all()
                        below.

    sv_clean_all() / do_clean_all()
                        SvREFCNT_dec(sv) each remaining SV, possibly
                        triggering an sv_free(). It also sets the
                        SVf_BREAK flag on the SV to indicate that the
                        refcnt has been artificially lowered, and thus
                        stopping sv_free() from giving spurious warnings
                        about SVs which unexpectedly have a refcnt
                        of zero.  called repeatedly from perl_destruct()
                        until there are no SVs left.

=head2 Arena allocator API Summary

Private API to rest of sv.c

    new_SV(),  del_SV(),

    new_XIV(), del_XIV(),
    new_XNV(), del_XNV(),
    etc

Public API:

    sv_report_used(), sv_clean_objs(), sv_clean_all(), sv_free_arenas()

=cut

============================================================================ */

/*
 * "A time to plant, and a time to uproot what was planted..."
 */

/*
 * nice_chunk and nice_chunk size need to be set
 * and queried under the protection of sv_mutex
 */
void
Perl_offer_nice_chunk(pTHX_ void *chunk, U32 chunk_size)
{
    dVAR;
    void *new_chunk;
    U32 new_chunk_size;
    LOCK_SV_MUTEX;
    new_chunk = (void *)(chunk);
    new_chunk_size = (chunk_size);
    if (new_chunk_size > PL_nice_chunk_size) {
        Safefree(PL_nice_chunk);
        PL_nice_chunk = (char *) new_chunk;
        PL_nice_chunk_size = new_chunk_size;
    } else {
        Safefree(chunk);
    }
    UNLOCK_SV_MUTEX;
}

#ifdef DEBUG_LEAKING_SCALARS
#  define FREE_SV_DEBUG_FILE(sv) Safefree((sv)->sv_debug_file)
#else
#  define FREE_SV_DEBUG_FILE(sv)
#endif

#ifdef PERL_POISON
#  define SvARENA_CHAIN(sv)     ((sv)->sv_u.svu_rv)
/* Whilst I'd love to do this, it seems that things like to check on
   unreferenced scalars
#  define POSION_SV_HEAD(sv)    PoisonNew(sv, 1, struct STRUCT_SV)
*/
#  define POSION_SV_HEAD(sv)    PoisonNew(&SvANY(sv), 1, void *), \
                                PoisonNew(&SvREFCNT(sv), 1, U32)
#else
#  define SvARENA_CHAIN(sv)     SvANY(sv)
#  define POSION_SV_HEAD(sv)
#endif

#define plant_SV(p) \
    STMT_START {                                        \
        FREE_SV_DEBUG_FILE(p);                          \
        POSION_SV_HEAD(p);                              \
        SvARENA_CHAIN(p) = (void *)PL_sv_root;          \
        SvFLAGS(p) = SVTYPEMASK;                        \
        PL_sv_root = (p);                               \
        --PL_sv_count;                                  \
    } STMT_END

/* sv_mutex must be held while calling uproot_SV() */
#define uproot_SV(p) \
    STMT_START {                                        \
        (p) = PL_sv_root;                               \
        PL_sv_root = (SV*)SvARENA_CHAIN(p);             \
        ++PL_sv_count;                                  \
    } STMT_END


/* make some more SVs by adding another arena */

/* sv_mutex must be held while calling more_sv() */
STATIC SV*
S_more_sv(pTHX)
{
    dVAR;
    SV* sv;

    if (PL_nice_chunk) {
        sv_add_arena(PL_nice_chunk, PL_nice_chunk_size, 0);
        PL_nice_chunk = NULL;
        PL_nice_chunk_size = 0;
    }
    else {
        char *chunk;                /* must use New here to match call to */
        Newx(chunk,PERL_ARENA_SIZE,char);  /* Safefree() in sv_free_arenas() */
        sv_add_arena(chunk, PERL_ARENA_SIZE, 0);
    }
    uproot_SV(sv);
    return sv;
}

/* new_SV(): return a new, empty SV head */

#ifdef DEBUG_LEAKING_SCALARS
/* provide a real function for a debugger to play with */
STATIC SV*
S_new_SV(pTHX)
{
    SV* sv;

    LOCK_SV_MUTEX;
    if (PL_sv_root)
        uproot_SV(sv);
    else
        sv = S_more_sv(aTHX);
    UNLOCK_SV_MUTEX;
    SvANY(sv) = 0;
    SvREFCNT(sv) = 1;
    SvFLAGS(sv) = 0;
    sv->sv_debug_optype = PL_op ? PL_op->op_type : 0;
    sv->sv_debug_line = (U16) ((PL_copline == NOLINE) ?
        (PL_curcop ? CopLINE(PL_curcop) : 0) : PL_copline);
    sv->sv_debug_inpad = 0;
    sv->sv_debug_cloned = 0;
    sv->sv_debug_file = PL_curcop ? savepv(CopFILE(PL_curcop)): NULL;
    
    return sv;
}
#  define new_SV(p) (p)=S_new_SV(aTHX)

#else
#  define new_SV(p) \
    STMT_START {                                        \
        LOCK_SV_MUTEX;                                  \
        if (PL_sv_root)                                 \
            uproot_SV(p);                               \
        else                                            \
            (p) = S_more_sv(aTHX);                      \
        UNLOCK_SV_MUTEX;                                \
        SvANY(p) = 0;                                   \
        SvREFCNT(p) = 1;                                \
        SvFLAGS(p) = 0;                                 \
    } STMT_END
#endif


/* del_SV(): return an empty SV head to the free list */

#ifdef DEBUGGING

#define del_SV(p) \
    STMT_START {                                        \
        LOCK_SV_MUTEX;                                  \
        if (DEBUG_D_TEST)                               \
            del_sv(p);                                  \
        else                                            \
            plant_SV(p);                                \
        UNLOCK_SV_MUTEX;                                \
    } STMT_END

STATIC void
S_del_sv(pTHX_ SV *p)
{
    dVAR;
    if (DEBUG_D_TEST) {
        SV* sva;
        bool ok = 0;
        for (sva = PL_sv_arenaroot; sva; sva = (SV *) SvANY(sva)) {
            const SV * const sv = sva + 1;
            const SV * const svend = &sva[SvREFCNT(sva)];
            if (p >= sv && p < svend) {
                ok = 1;
                break;
            }
        }
        if (!ok) {
            if (ckWARN_d(WARN_INTERNAL))        
                Perl_warner(aTHX_ packWARN(WARN_INTERNAL),
                            "Attempt to free non-arena SV: 0x%"UVxf
                            pTHX__FORMAT, PTR2UV(p) pTHX__VALUE);
            return;
        }
    }
    plant_SV(p);
}

#else /* ! DEBUGGING */

#define del_SV(p)   plant_SV(p)

#endif /* DEBUGGING */


/*
=head1 SV Manipulation Functions

=for apidoc sv_add_arena

Given a chunk of memory, link it to the head of the list of arenas,
and split it into a list of free SVs.

=cut
*/

void
Perl_sv_add_arena(pTHX_ char *ptr, U32 size, U32 flags)
{
    dVAR;
    SV* const sva = (SV*)ptr;
    register SV* sv;
    register SV* svend;

    /* The first SV in an arena isn't an SV. */
    SvANY(sva) = (void *) PL_sv_arenaroot;              /* ptr to next arena */
    SvREFCNT(sva) = size / sizeof(SV);          /* number of SV slots */
    SvFLAGS(sva) = flags;                       /* FAKE if not to be freed */

    PL_sv_arenaroot = sva;
    PL_sv_root = sva + 1;

    svend = &sva[SvREFCNT(sva) - 1];
    sv = sva + 1;
    while (sv < svend) {
        SvARENA_CHAIN(sv) = (void *)(SV*)(sv + 1);
#ifdef DEBUGGING
        SvREFCNT(sv) = 0;
#endif
        /* Must always set typemask because it's awlays checked in on cleanup
           when the arenas are walked looking for objects.  */
        SvFLAGS(sv) = SVTYPEMASK;
        sv++;
    }
    SvARENA_CHAIN(sv) = 0;
#ifdef DEBUGGING
    SvREFCNT(sv) = 0;
#endif
    SvFLAGS(sv) = SVTYPEMASK;
}

/* visit(): call the named function for each non-free SV in the arenas
 * whose flags field matches the flags/mask args. */

STATIC I32
S_visit(pTHX_ SVFUNC_t f, U32 flags, U32 mask)
{
    dVAR;
    SV* sva;
    I32 visited = 0;

    for (sva = PL_sv_arenaroot; sva; sva = (SV*)SvANY(sva)) {
        register const SV * const svend = &sva[SvREFCNT(sva)];
        register SV* sv;
        for (sv = sva + 1; sv < svend; ++sv) {
            if (SvTYPE(sv) != SVTYPEMASK
                    && (sv->sv_flags & mask) == flags
                    && SvREFCNT(sv))
            {
                (FCALL)(aTHX_ sv);
                ++visited;
            }
        }
    }
    return visited;
}

#ifdef DEBUGGING

/* called by sv_report_used() for each live SV */

static void
do_report_used(pTHX_ SV *sv)
{
    if (SvTYPE(sv) != SVTYPEMASK) {
        PerlIO_printf(Perl_debug_log, "****\n");
        sv_dump(sv);
    }
}
#endif

/*
=for apidoc sv_report_used

Dump the contents of all SVs not yet freed. (Debugging aid).

=cut
*/

void
Perl_sv_report_used(pTHX)
{
#ifdef DEBUGGING
    visit(do_report_used, 0, 0);
#else
    PERL_UNUSED_CONTEXT;
#endif
}

/* called by sv_clean_objs() for each live SV */

static void
do_clean_objs(pTHX_ SV *ref)
{
    dVAR;
    if (SvROK(ref)) {
        SV * const target = SvRV(ref);
        if (SvOBJECT(target)) {
            DEBUG_D((PerlIO_printf(Perl_debug_log, "Cleaning object ref:\n "), sv_dump(ref)));
            if (SvWEAKREF(ref)) {
                sv_del_backref(target, ref);
                SvWEAKREF_off(ref);
                SvRV_set(ref, NULL);
            } else {
                SvROK_off(ref);
                SvRV_set(ref, NULL);
                SvREFCNT_dec(target);
            }
        }
    }

    /* XXX Might want to check arrays, etc. */
}

/* called by sv_clean_objs() for each live SV */

#ifndef DISABLE_DESTRUCTOR_KLUDGE
static void
do_clean_named_objs(pTHX_ SV *sv)
{
    dVAR;
    if (SvTYPE(sv) == SVt_PVGV && isGV_with_GP(sv) && GvGP(sv)) {
        if ((
#ifdef PERL_DONT_CREATE_GVSV
             GvSV(sv) &&
#endif
             SvOBJECT(GvSV(sv))) ||
             (GvAV(sv) && SvOBJECT(GvAV(sv))) ||
             (GvHV(sv) && SvOBJECT(GvHV(sv))) ||
             (GvIO(sv) && SvOBJECT(GvIO(sv))) ||
             (GvCV(sv) && SvOBJECT(GvCV(sv))) )
        {
            DEBUG_D((PerlIO_printf(Perl_debug_log, "Cleaning named glob object:\n "), sv_dump(sv)));
            SvFLAGS(sv) |= SVf_BREAK;
            SvREFCNT_dec(sv);
        }
    }
}
#endif

/*
=for apidoc sv_clean_objs

Attempt to destroy all objects not yet freed

=cut
*/

void
Perl_sv_clean_objs(pTHX)
{
    dVAR;
    PL_in_clean_objs = TRUE;
    visit(do_clean_objs, SVf_ROK, SVf_ROK);
#ifndef DISABLE_DESTRUCTOR_KLUDGE
    /* some barnacles may yet remain, clinging to typeglobs */
    visit(do_clean_named_objs, SVt_PVGV, SVTYPEMASK);
#endif
    PL_in_clean_objs = FALSE;
}

/* called by sv_clean_all() for each live SV */

static void
do_clean_all(pTHX_ SV *sv)
{
    dVAR;
    DEBUG_D((PerlIO_printf(Perl_debug_log, "Cleaning loops: SV at 0x%"UVxf"\n", PTR2UV(sv)) ));
    SvFLAGS(sv) |= SVf_BREAK;
    if (PL_comppad == (AV*)sv) {
        PL_comppad = NULL;
        PL_curpad = NULL;
    }
    SvREFCNT_dec(sv);
}

/*
=for apidoc sv_clean_all

Decrement the refcnt of each remaining SV, possibly triggering a
cleanup. This function may have to be called multiple times to free
SVs which are in complex self-referential hierarchies.

=cut
*/

I32
Perl_sv_clean_all(pTHX)
{
    dVAR;
    I32 cleaned;
    PL_in_clean_all = TRUE;
    cleaned = visit(do_clean_all, 0,0);
    PL_in_clean_all = FALSE;
    return cleaned;
}

/*
  ARENASETS: a meta-arena implementation which separates arena-info
  into struct arena_set, which contains an array of struct
  arena_descs, each holding info for a single arena.  By separating
  the meta-info from the arena, we recover the 1st slot, formerly
  borrowed for list management.  The arena_set is about the size of an
  arena, avoiding the needless malloc overhead of a naive linked-list

  The cost is 1 arena-set malloc per ~320 arena-mallocs, + the unused
  memory in the last arena-set (1/2 on average).  In trade, we get
  back the 1st slot in each arena (ie 1.7% of a CV-arena, less for
  smaller types).  The recovery of the wasted space allows use of
  small arenas for large, rare body types,
*/
struct arena_desc {
    char       *arena;          /* the raw storage, allocated aligned */
    size_t      size;           /* its size ~4k typ */
    int         unit_type;      /* useful for arena audits */
    /* info for sv-heads (eventually)
       int count, flags;
    */
};

struct arena_set;

/* Get the maximum number of elements in set[] such that struct arena_set
   will fit within PERL_ARENA_SIZE, which is probabably just under 4K, and
   therefore likely to be 1 aligned memory page.  */

#define ARENAS_PER_SET  ((PERL_ARENA_SIZE - sizeof(struct arena_set*) \
                          - 2 * sizeof(int)) / sizeof (struct arena_desc))

struct arena_set {
    struct arena_set* next;
    int   set_size;             /* ie ARENAS_PER_SET */
    int   curr;                 /* index of next available arena-desc */
    struct arena_desc set[ARENAS_PER_SET];
};

/*
=for apidoc sv_free_arenas

Deallocate the memory used by all arenas. Note that all the individual SV
heads and bodies within the arenas must already have been freed.

=cut
*/
void
Perl_sv_free_arenas(pTHX)
{
    dVAR;
    SV* sva;
    SV* svanext;
    int i;

    /* Free arenas here, but be careful about fake ones.  (We assume
       contiguity of the fake ones with the corresponding real ones.) */

    for (sva = PL_sv_arenaroot; sva; sva = svanext) {
        svanext = (SV*) SvANY(sva);
        while (svanext && SvFAKE(svanext))
            svanext = (SV*) SvANY(svanext);

        if (!SvFAKE(sva))
            Safefree(sva);
    }

    {
        struct arena_set *next, *aroot = (struct arena_set*) PL_body_arenas;
        
        for (; aroot; aroot = next) {
            const int max = aroot->curr;
            for (i=0; i<max; i++) {
                assert(aroot->set[i].arena);
                Safefree(aroot->set[i].arena);
            }
            next = aroot->next;
            Safefree(aroot);
        }
    }
    PL_body_arenas = 0;

    for (i=0; i<PERL_ARENA_ROOTS_SIZE; i++)
        PL_body_roots[i] = 0;

    Safefree(PL_nice_chunk);
    PL_nice_chunk = NULL;
    PL_nice_chunk_size = 0;
    PL_sv_arenaroot = 0;
    PL_sv_root = 0;
}

/*
  Here are mid-level routines that manage the allocation of bodies out
  of the various arenas.  There are 5 kinds of arenas:

  1. SV-head arenas, which are discussed and handled above
  2. regular body arenas
  3. arenas for reduced-size bodies
  4. Hash-Entry arenas
  5. pte arenas (thread related)

  Arena types 2 & 3 are chained by body-type off an array of
  arena-root pointers, which is indexed by svtype.  Some of the
  larger/less used body types are malloced singly, since a large
  unused block of them is wasteful.  Also, several svtypes dont have
  bodies; the data fits into the sv-head itself.  The arena-root
  pointer thus has a few unused root-pointers (which may be hijacked
  later for arena types 4,5)

  3 differs from 2 as an optimization; some body types have several
  unused fields in the front of the structure (which are kept in-place
  for consistency).  These bodies can be allocated in smaller chunks,
  because the leading fields arent accessed.  Pointers to such bodies
  are decremented to point at the unused 'ghost' memory, knowing that
  the pointers are used with offsets to the real memory.

  HE, HEK arenas are managed separately, with separate code, but may
  be merge-able later..

  PTE arenas are not sv-bodies, but they share these mid-level
  mechanics, so are considered here.  The new mid-level mechanics rely
  on the sv_type of the body being allocated, so we just reserve one
  of the unused body-slots for PTEs, then use it in those (2) PTE
  contexts below (line ~10k)
*/

/* get_arena(size): this creates custom-sized arenas
   TBD: export properly for hv.c: S_more_he().
*/
void*
Perl_get_arena(pTHX_ int arena_size)
{
    dVAR;
    struct arena_desc* adesc;
    struct arena_set *newroot, **aroot = (struct arena_set**) &PL_body_arenas;
    int curr;

    /* shouldnt need this
    if (!arena_size)    arena_size = PERL_ARENA_SIZE;
    */

    /* may need new arena-set to hold new arena */
    if (!*aroot || (*aroot)->curr >= (*aroot)->set_size) {
        Newxz(newroot, 1, struct arena_set);
        newroot->set_size = ARENAS_PER_SET;
        newroot->next = *aroot;
        *aroot = newroot;
        DEBUG_m(PerlIO_printf(Perl_debug_log, "new arenaset %p\n", (void*)*aroot));
    }

    /* ok, now have arena-set with at least 1 empty/available arena-desc */
    curr = (*aroot)->curr++;
    adesc = &((*aroot)->set[curr]);
    assert(!adesc->arena);
    
    Newxz(adesc->arena, arena_size, char);
    adesc->size = arena_size;
    DEBUG_m(PerlIO_printf(Perl_debug_log, "arena %d added: %p size %d\n", 
                          curr, adesc->arena, arena_size));

    return adesc->arena;
}


/* return a thing to the free list */

#define del_body(thing, root)                   \
    STMT_START {                                \
        void ** const thing_copy = (void **)thing;\
        LOCK_SV_MUTEX;                          \
        *thing_copy = *root;                    \
        *root = (void*)thing_copy;              \
        UNLOCK_SV_MUTEX;                        \
    } STMT_END

/* 

=head1 SV-Body Allocation

Allocation of SV-bodies is similar to SV-heads, differing as follows;
the allocation mechanism is used for many body types, so is somewhat
more complicated, it uses arena-sets, and has no need for still-live
SV detection.

At the outermost level, (new|del)_X*V macros return bodies of the
appropriate type.  These macros call either (new|del)_body_type or
(new|del)_body_allocated macro pairs, depending on specifics of the
type.  Most body types use the former pair, the latter pair is used to
allocate body types with "ghost fields".

"ghost fields" are fields that are unused in certain types, and
consequently dont need to actually exist.  They are declared because
they're part of a "base type", which allows use of functions as
methods.  The simplest examples are AVs and HVs, 2 aggregate types
which don't use the fields which support SCALAR semantics.

For these types, the arenas are carved up into *_allocated size
chunks, we thus avoid wasted memory for those unaccessed members.
When bodies are allocated, we adjust the pointer back in memory by the
size of the bit not allocated, so it's as if we allocated the full
structure.  (But things will all go boom if you write to the part that
is "not there", because you'll be overwriting the last members of the
preceding structure in memory.)

We calculate the correction using the STRUCT_OFFSET macro. For
example, if xpv_allocated is the same structure as XPV then the two
OFFSETs sum to zero, and the pointer is unchanged. If the allocated
structure is smaller (no initial NV actually allocated) then the net
effect is to subtract the size of the NV from the pointer, to return a
new pointer as if an initial NV were actually allocated.

This is the same trick as was used for NV and IV bodies. Ironically it
doesn't need to be used for NV bodies any more, because NV is now at
the start of the structure. IV bodies don't need it either, because
they are no longer allocated.

In turn, the new_body_* allocators call S_new_body(), which invokes
new_body_inline macro, which takes a lock, and takes a body off the
linked list at PL_body_roots[sv_type], calling S_more_bodies() if
necessary to refresh an empty list.  Then the lock is released, and
the body is returned.

S_more_bodies calls get_arena(), and carves it up into an array of N
bodies, which it strings into a linked list.  It looks up arena-size
and body-size from the body_details table described below, thus
supporting the multiple body-types.

If PURIFY is defined, or PERL_ARENA_SIZE=0, arenas are not used, and
the (new|del)_X*V macros are mapped directly to malloc/free.

*/

/* 

For each sv-type, struct body_details bodies_by_type[] carries
parameters which control these aspects of SV handling:

Arena_size determines whether arenas are used for this body type, and if
so, how big they are.  PURIFY or PERL_ARENA_SIZE=0 set this field to
zero, forcing individual mallocs and frees.

Body_size determines how big a body is, and therefore how many fit into
each arena.  Offset carries the body-pointer adjustment needed for
*_allocated body types, and is used in *_allocated macros.

But its main purpose is to parameterize info needed in
Perl_sv_upgrade().  The info here dramatically simplifies the function
vs the implementation in 5.8.7, making it table-driven.  All fields
are used for this, except for arena_size.

For the sv-types that have no bodies, arenas are not used, so those
PL_body_roots[sv_type] are unused, and can be overloaded.  In
something of a special case, SVt_NULL is borrowed for HE arenas;
PL_body_roots[SVt_NULL] is filled by S_more_he, but the
bodies_by_type[SVt_NULL] slot is not used, as the table is not
available in hv.c,

PTEs also use arenas, but are never seen in Perl_sv_upgrade.
Nonetheless, they get their own slot in bodies_by_type[SVt_NULL], so
they can just use the same allocation semantics.  At first, PTEs were
also overloaded to a non-body sv-type, but this yielded hard-to-find
malloc bugs, so was simplified by claiming a new slot.  This choice
has no consequence at this time.

*/

struct body_details {
    U8 body_size;       /* Size to allocate  */
    U8 copy;            /* Size of structure to copy (may be shorter)  */
    U8 offset;
    unsigned int type : 4;          /* We have space for a sanity check.  */
    unsigned int cant_upgrade : 1;  /* Cannot upgrade this type */
    unsigned int zero_nv : 1;       /* zero the NV when upgrading from this */
    unsigned int arena : 1;         /* Allocated from an arena */
    size_t arena_size;              /* Size of arena to allocate */
};

#define HADNV FALSE
#define NONV TRUE


#ifdef PURIFY
/* With -DPURFIY we allocate everything directly, and don't use arenas.
   This seems a rather elegant way to simplify some of the code below.  */
#define HASARENA FALSE
#else
#define HASARENA TRUE
#endif
#define NOARENA FALSE

/* Size the arenas to exactly fit a given number of bodies.  A count
   of 0 fits the max number bodies into a PERL_ARENA_SIZE.block,
   simplifying the default.  If count > 0, the arena is sized to fit
   only that many bodies, allowing arenas to be used for large, rare
   bodies (XPVFM, XPVIO) without undue waste.  The arena size is
   limited by PERL_ARENA_SIZE, so we can safely oversize the
   declarations.
 */
#define FIT_ARENA0(body_size)                           \
    ((size_t)(PERL_ARENA_SIZE / body_size) * body_size)
#define FIT_ARENAn(count,body_size)                     \
    ( count * body_size <= PERL_ARENA_SIZE)             \
    ? count * body_size                                 \
    : FIT_ARENA0 (body_size)
#define FIT_ARENA(count,body_size)                      \
    count                                               \
    ? FIT_ARENAn (count, body_size)                     \
    : FIT_ARENA0 (body_size)

/* A macro to work out the offset needed to subtract from a pointer to (say)

typedef struct {
    STRLEN      xpv_cur;
    STRLEN      xpv_len;
} xpv_allocated;

to make its members accessible via a pointer to (say)

struct xpv {
    NV          xnv_nv;
    STRLEN      xpv_cur;
    STRLEN      xpv_len;
};

*/

#define relative_STRUCT_OFFSET(longer, shorter, member) \
    (STRUCT_OFFSET(shorter, member) - STRUCT_OFFSET(longer, member))

/* Calculate the length to copy. Specifically work out the length less any
   final padding the compiler needed to add.  See the comment in sv_upgrade
   for why copying the padding proved to be a bug.  */

#define copy_length(type, last_member) \
        STRUCT_OFFSET(type, last_member) \
        + sizeof (((type*)SvANY((SV*)0))->last_member)

static const struct body_details bodies_by_type[] = {
    { sizeof(HE), 0, 0, SVt_NULL,
      FALSE, NONV, NOARENA, FIT_ARENA(0, sizeof(HE)) },

    /* The bind placeholder pretends to be an RV for now.
       Also it's marked as "can't upgrade" top stop anyone using it before it's
       implemented.  */
    { 0, 0, 0, SVt_BIND, TRUE, NONV, NOARENA, 0 },

    /* IVs are in the head, so the allocation size is 0.
       However, the slot is overloaded for PTEs.  */
    { sizeof(struct ptr_tbl_ent), /* This is used for PTEs.  */
      sizeof(IV), /* This is used to copy out the IV body.  */
      STRUCT_OFFSET(XPVIV, xiv_iv), SVt_IV, FALSE, NONV,
      NOARENA /* IVS don't need an arena  */,
      /* But PTEs need to know the size of their arena  */
      FIT_ARENA(0, sizeof(struct ptr_tbl_ent))
    },

    /* 8 bytes on most ILP32 with IEEE doubles */
    { sizeof(NV), sizeof(NV), 0, SVt_NV, FALSE, HADNV, HASARENA,
      FIT_ARENA(0, sizeof(NV)) },

    /* RVs are in the head now.  */
    { 0, 0, 0, SVt_RV, FALSE, NONV, NOARENA, 0 },

    /* 8 bytes on most ILP32 with IEEE doubles */
    { sizeof(xpv_allocated),
      copy_length(XPV, xpv_len)
      - relative_STRUCT_OFFSET(xpv_allocated, XPV, xpv_cur),
      + relative_STRUCT_OFFSET(xpv_allocated, XPV, xpv_cur),
      SVt_PV, FALSE, NONV, HASARENA, FIT_ARENA(0, sizeof(xpv_allocated)) },

    /* 12 */
    { sizeof(xpviv_allocated),
      copy_length(XPVIV, xiv_u)
      - relative_STRUCT_OFFSET(xpviv_allocated, XPVIV, xpv_cur),
      + relative_STRUCT_OFFSET(xpviv_allocated, XPVIV, xpv_cur),
      SVt_PVIV, FALSE, NONV, HASARENA, FIT_ARENA(0, sizeof(xpviv_allocated)) },

    /* 20 */
    { sizeof(XPVNV), copy_length(XPVNV, xiv_u), 0, SVt_PVNV, FALSE, HADNV,
      HASARENA, FIT_ARENA(0, sizeof(XPVNV)) },

    /* 28 */
    { sizeof(XPVMG), copy_length(XPVMG, xmg_stash), 0, SVt_PVMG, FALSE, HADNV,
      HASARENA, FIT_ARENA(0, sizeof(XPVMG)) },
    
    /* 48 */
    { sizeof(XPVGV), sizeof(XPVGV), 0, SVt_PVGV, TRUE, HADNV,
      HASARENA, FIT_ARENA(0, sizeof(XPVGV)) },
    
    /* 64 */
    { sizeof(XPVLV), sizeof(XPVLV), 0, SVt_PVLV, TRUE, HADNV,
      HASARENA, FIT_ARENA(0, sizeof(XPVLV)) },

    { sizeof(xpvav_allocated),
      copy_length(XPVAV, xmg_stash)
      - relative_STRUCT_OFFSET(xpvav_allocated, XPVAV, xav_fill),
      + relative_STRUCT_OFFSET(xpvav_allocated, XPVAV, xav_fill),
      SVt_PVAV, TRUE, HADNV, HASARENA, FIT_ARENA(0, sizeof(xpvav_allocated)) },

    { sizeof(xpvhv_allocated),
      copy_length(XPVHV, xmg_stash)
      - relative_STRUCT_OFFSET(xpvhv_allocated, XPVHV, xhv_fill),
      + relative_STRUCT_OFFSET(xpvhv_allocated, XPVHV, xhv_fill),
      SVt_PVHV, TRUE, HADNV, HASARENA, FIT_ARENA(0, sizeof(xpvhv_allocated)) },

    /* 56 */
    { sizeof(xpvcv_allocated), sizeof(xpvcv_allocated),
      + relative_STRUCT_OFFSET(xpvcv_allocated, XPVCV, xpv_cur),
      SVt_PVCV, TRUE, NONV, HASARENA, FIT_ARENA(0, sizeof(xpvcv_allocated)) },

    { sizeof(xpvfm_allocated), sizeof(xpvfm_allocated),
      + relative_STRUCT_OFFSET(xpvfm_allocated, XPVFM, xpv_cur),
      SVt_PVFM, TRUE, NONV, NOARENA, FIT_ARENA(20, sizeof(xpvfm_allocated)) },

    /* XPVIO is 84 bytes, fits 48x */
    { sizeof(XPVIO), sizeof(XPVIO), 0, SVt_PVIO, TRUE, HADNV,
      HASARENA, FIT_ARENA(24, sizeof(XPVIO)) },
};

#define new_body_type(sv_type)          \
    (void *)((char *)S_new_body(aTHX_ sv_type))

#define del_body_type(p, sv_type)       \
    del_body(p, &PL_body_roots[sv_type])


#define new_body_allocated(sv_type)             \
    (void *)((char *)S_new_body(aTHX_ sv_type)  \
             - bodies_by_type[sv_type].offset)

#define del_body_allocated(p, sv_type)          \
    del_body(p + bodies_by_type[sv_type].offset, &PL_body_roots[sv_type])


#define my_safemalloc(s)        (void*)safemalloc(s)
#define my_safecalloc(s)        (void*)safecalloc(s, 1)
#define my_safefree(p)  safefree((char*)p)

#ifdef PURIFY

#define new_XNV()       my_safemalloc(sizeof(XPVNV))
#define del_XNV(p)      my_safefree(p)

#define new_XPVNV()     my_safemalloc(sizeof(XPVNV))
#define del_XPVNV(p)    my_safefree(p)

#define new_XPVAV()     my_safemalloc(sizeof(XPVAV))
#define del_XPVAV(p)    my_safefree(p)

#define new_XPVHV()     my_safemalloc(sizeof(XPVHV))
#define del_XPVHV(p)    my_safefree(p)

#define new_XPVMG()     my_safemalloc(sizeof(XPVMG))
#define del_XPVMG(p)    my_safefree(p)

#define new_XPVGV()     my_safemalloc(sizeof(XPVGV))
#define del_XPVGV(p)    my_safefree(p)

#else /* !PURIFY */

#define new_XNV()       new_body_type(SVt_NV)
#define del_XNV(p)      del_body_type(p, SVt_NV)

#define new_XPVNV()     new_body_type(SVt_PVNV)
#define del_XPVNV(p)    del_body_type(p, SVt_PVNV)

#define new_XPVAV()     new_body_allocated(SVt_PVAV)
#define del_XPVAV(p)    del_body_allocated(p, SVt_PVAV)

#define new_XPVHV()     new_body_allocated(SVt_PVHV)
#define del_XPVHV(p)    del_body_allocated(p, SVt_PVHV)

#define new_XPVMG()     new_body_type(SVt_PVMG)
#define del_XPVMG(p)    del_body_type(p, SVt_PVMG)

#define new_XPVGV()     new_body_type(SVt_PVGV)
#define del_XPVGV(p)    del_body_type(p, SVt_PVGV)

#endif /* PURIFY */

/* no arena for you! */

#define new_NOARENA(details) \
        my_safemalloc((details)->body_size + (details)->offset)
#define new_NOARENAZ(details) \
        my_safecalloc((details)->body_size + (details)->offset)

#if defined(DEBUGGING) && !defined(PERL_GLOBAL_STRUCT_PRIVATE)
static bool done_sanity_check;
#endif

STATIC void *
S_more_bodies (pTHX_ svtype sv_type)
{
    dVAR;
    void ** const root = &PL_body_roots[sv_type];
    const struct body_details * const bdp = &bodies_by_type[sv_type];
    const size_t body_size = bdp->body_size;
    char *start;
    const char *end;

    assert(bdp->arena_size);

#if defined(DEBUGGING) && !defined(PERL_GLOBAL_STRUCT_PRIVATE)
    /* PERL_GLOBAL_STRUCT_PRIVATE cannot coexist with global
     * variables like done_sanity_check. */
    if (!done_sanity_check) {
        unsigned int i = SVt_LAST;

        done_sanity_check = TRUE;

        while (i--)
            assert (bodies_by_type[i].type == i);
    }
#endif

    start = (char*) Perl_get_arena(aTHX_ bdp->arena_size);

    end = start + bdp->arena_size - body_size;

    /* computed count doesnt reflect the 1st slot reservation */
    DEBUG_m(PerlIO_printf(Perl_debug_log,
                          "arena %p end %p arena-size %d type %d size %d ct %d\n",
                          start, end,
                          (int)bdp->arena_size, sv_type, (int)body_size,
                          (int)bdp->arena_size / (int)body_size));

    *root = (void *)start;

    while (start < end) {
        char * const next = start + body_size;
        *(void**) start = (void *)next;
        start = next;
    }
    *(void **)start = 0;

    return *root;
}

/* grab a new thing from the free list, allocating more if necessary.
   The inline version is used for speed in hot routines, and the
   function using it serves the rest (unless PURIFY).
*/
#define new_body_inline(xpv, sv_type) \
    STMT_START { \
        void ** const r3wt = &PL_body_roots[sv_type]; \
        LOCK_SV_MUTEX; \
        xpv = (PTR_TBL_ENT_t*) (*((void **)(r3wt))      \
          ? *((void **)(r3wt)) : more_bodies(sv_type)); \
        *(r3wt) = *(void**)(xpv); \
        UNLOCK_SV_MUTEX; \
    } STMT_END

#ifndef PURIFY

STATIC void *
S_new_body(pTHX_ svtype sv_type)
{
    dVAR;
    void *xpv;
    new_body_inline(xpv, sv_type);
    return xpv;
}

#endif

/*
=for apidoc sv_upgrade

Upgrade an SV to a more complex form.  Generally adds a new body type to the
SV, then copies across as much information as possible from the old body.
You generally want to use the C<SvUPGRADE> macro wrapper. See also C<svtype>.

=cut
*/

void
Perl_sv_upgrade(pTHX_ register SV *sv, svtype new_type)
{
    dVAR;
    void*       old_body;
    void*       new_body;
    const svtype old_type = SvTYPE(sv);
    const struct body_details *new_type_details;
    const struct body_details *const old_type_details
        = bodies_by_type + old_type;

    if (new_type != SVt_PV && SvIsCOW(sv)) {
        sv_force_normal_flags(sv, 0);
    }

    if (old_type == new_type)
        return;

    if (old_type > new_type)
        Perl_croak(aTHX_ "sv_upgrade from type %d down to type %d",
                (int)old_type, (int)new_type);


    old_body = SvANY(sv);

    /* Copying structures onto other structures that have been neatly zeroed
       has a subtle gotcha. Consider XPVMG

       +------+------+------+------+------+-------+-------+
       |     NV      | CUR  | LEN  |  IV  | MAGIC | STASH |
       +------+------+------+------+------+-------+-------+
       0      4      8     12     16     20      24      28

       where NVs are aligned to 8 bytes, so that sizeof that structure is
       actually 32 bytes long, with 4 bytes of padding at the end:

       +------+------+------+------+------+-------+-------+------+
       |     NV      | CUR  | LEN  |  IV  | MAGIC | STASH | ???  |
       +------+------+------+------+------+-------+-------+------+
       0      4      8     12     16     20      24      28     32

       so what happens if you allocate memory for this structure:

       +------+------+------+------+------+-------+-------+------+------+...
       |     NV      | CUR  | LEN  |  IV  | MAGIC | STASH |  GP  | NAME |
       +------+------+------+------+------+-------+-------+------+------+...
       0      4      8     12     16     20      24      28     32     36

       zero it, then copy sizeof(XPVMG) bytes on top of it? Not quite what you
       expect, because you copy the area marked ??? onto GP. Now, ??? may have
       started out as zero once, but it's quite possible that it isn't. So now,
       rather than a nicely zeroed GP, you have it pointing somewhere random.
       Bugs ensue.

       (In fact, GP ends up pointing at a previous GP structure, because the
       principle cause of the padding in XPVMG getting garbage is a copy of
       sizeof(XPVMG) bytes from a XPVGV structure in sv_unglob. Right now
       this happens to be moot because XPVGV has been re-ordered, with GP
       no longer after STASH)

       So we are careful and work out the size of used parts of all the
       structures.  */

    switch (old_type) {
    case SVt_NULL:
        break;
    case SVt_IV:
        if (new_type < SVt_PVIV) {
            new_type = (new_type == SVt_NV)
                ? SVt_PVNV : SVt_PVIV;
        }
        break;
    case SVt_NV:
        if (new_type < SVt_PVNV) {
            new_type = SVt_PVNV;
        }
        break;
    case SVt_RV:
        break;
    case SVt_PV:
        assert(new_type > SVt_PV);
        assert(SVt_IV < SVt_PV);
        assert(SVt_NV < SVt_PV);
        break;
    case SVt_PVIV:
        break;
    case SVt_PVNV:
        break;
    case SVt_PVMG:
        /* Because the XPVMG of PL_mess_sv isn't allocated from the arena,
           there's no way that it can be safely upgraded, because perl.c
           expects to Safefree(SvANY(PL_mess_sv))  */
        assert(sv != PL_mess_sv);
        /* This flag bit is used to mean other things in other scalar types.
           Given that it only has meaning inside the pad, it shouldn't be set
           on anything that can get upgraded.  */
        assert(!SvPAD_TYPED(sv));
        break;
    default:
        if (old_type_details->cant_upgrade)
            Perl_croak(aTHX_ "Can't upgrade %s (%" UVuf ") to %" UVuf,
                       sv_reftype(sv, 0), (UV) old_type, (UV) new_type);
    }
    new_type_details = bodies_by_type + new_type;

    SvFLAGS(sv) &= ~SVTYPEMASK;
    SvFLAGS(sv) |= new_type;

    /* This can't happen, as SVt_NULL is <= all values of new_type, so one of
       the return statements above will have triggered.  */
    assert (new_type != SVt_NULL);
    switch (new_type) {
    case SVt_IV:
        assert(old_type == SVt_NULL);
        SvANY(sv) = (XPVIV*)((char*)&(sv->sv_u.svu_iv) - STRUCT_OFFSET(XPVIV, xiv_iv));
        SvIV_set(sv, 0);
        return;
    case SVt_NV:
        assert(old_type == SVt_NULL);
        SvANY(sv) = new_XNV();
        SvNV_set(sv, 0);
        return;
    case SVt_RV:
        assert(old_type == SVt_NULL);
        SvANY(sv) = &sv->sv_u.svu_rv;
        SvRV_set(sv, 0);
        return;
    case SVt_PVHV:
    case SVt_PVAV:
        assert(new_type_details->body_size);

#ifndef PURIFY  
        assert(new_type_details->arena);
        assert(new_type_details->arena_size);
        /* This points to the start of the allocated area.  */
        new_body_inline(new_body, new_type);
        Zero(new_body, new_type_details->body_size, char);
        new_body = ((char *)new_body) - new_type_details->offset;
#else
        /* We always allocated the full length item with PURIFY. To do this
           we fake things so that arena is false for all 16 types..  */
        new_body = new_NOARENAZ(new_type_details);
#endif
        SvANY(sv) = new_body;
        if (new_type == SVt_PVAV) {
            AvMAX(sv)   = -1;
            AvFILLp(sv) = -1;
            AvREAL_only(sv);
        }

        /* SVt_NULL isn't the only thing upgraded to AV or HV.
           The target created by newSVrv also is, and it can have magic.
           However, it never has SvPVX set.
        */
        if (old_type >= SVt_RV) {
            assert(SvPVX_const(sv) == 0);
        }

        if (old_type >= SVt_PVMG) {
            SvMAGIC_set(sv, ((XPVMG*)old_body)->xmg_u.xmg_magic);
            SvSTASH_set(sv, ((XPVMG*)old_body)->xmg_stash);
        } else {
            sv->sv_u.svu_array = NULL; /* or svu_hash  */
        }
        break;


    case SVt_PVIV:
        /* XXX Is this still needed?  Was it ever needed?   Surely as there is
           no route from NV to PVIV, NOK can never be true  */
        assert(!SvNOKp(sv));
        assert(!SvNOK(sv));
    case SVt_PVIO:
    case SVt_PVFM:
    case SVt_PVGV:
    case SVt_PVCV:
    case SVt_PVLV:
    case SVt_PVMG:
    case SVt_PVNV:
    case SVt_PV:

        assert(new_type_details->body_size);
        /* We always allocated the full length item with PURIFY. To do this
           we fake things so that arena is false for all 16 types..  */
        if(new_type_details->arena) {
            /* This points to the start of the allocated area.  */
            new_body_inline(new_body, new_type);
            Zero(new_body, new_type_details->body_size, char);
            new_body = ((char *)new_body) - new_type_details->offset;
        } else {
            new_body = new_NOARENAZ(new_type_details);
        }
        SvANY(sv) = new_body;

        if (old_type_details->copy) {
            /* There is now the potential for an upgrade from something without
               an offset (PVNV or PVMG) to something with one (PVCV, PVFM)  */
            int offset = old_type_details->offset;
            int length = old_type_details->copy;

            if (new_type_details->offset > old_type_details->offset) {
                const int difference
                    = new_type_details->offset - old_type_details->offset;
                offset += difference;
                length -= difference;
            }
            assert (length >= 0);
                
            Copy((char *)old_body + offset, (char *)new_body + offset, length,
                 char);
        }

#ifndef NV_ZERO_IS_ALLBITS_ZERO
        /* If NV 0.0 is stores as all bits 0 then Zero() already creates a
         * correct 0.0 for us.  Otherwise, if the old body didn't have an
         * NV slot, but the new one does, then we need to initialise the
         * freshly created NV slot with whatever the correct bit pattern is
         * for 0.0  */
        if (old_type_details->zero_nv && !new_type_details->zero_nv)
            SvNV_set(sv, 0);
#endif

        if (new_type == SVt_PVIO)
            IoPAGE_LEN(sv) = 60;
        if (old_type < SVt_RV)
            SvPV_set(sv, NULL);
        break;
    default:
        Perl_croak(aTHX_ "panic: sv_upgrade to unknown type %lu",
                   (unsigned long)new_type);
    }

    if (old_type_details->arena) {
        /* If there was an old body, then we need to free it.
           Note that there is an assumption that all bodies of types that
           can be upgraded came from arenas. Only the more complex non-
           upgradable types are allowed to be directly malloc()ed.  */
#ifdef PURIFY
        my_safefree(old_body);
#else
        del_body((void*)((char*)old_body + old_type_details->offset),
                 &PL_body_roots[old_type]);
#endif
    }
}

/*
=for apidoc sv_backoff

Remove any string offset. You should normally use the C<SvOOK_off> macro
wrapper instead.

=cut
*/

int
Perl_sv_backoff(pTHX_ register SV *sv)
{
    PERL_UNUSED_CONTEXT;
    assert(SvOOK(sv));
    assert(SvTYPE(sv) != SVt_PVHV);
    assert(SvTYPE(sv) != SVt_PVAV);
    if (SvIVX(sv)) {
        const char * const s = SvPVX_const(sv);
        SvLEN_set(sv, SvLEN(sv) + SvIVX(sv));
        SvPV_set(sv, SvPVX(sv) - SvIVX(sv));
        SvIV_set(sv, 0);
        Move(s, SvPVX(sv), SvCUR(sv)+1, char);
    }
    SvFLAGS(sv) &= ~SVf_OOK;
    return 0;
}

/*
=for apidoc sv_grow

Expands the character buffer in the SV.  If necessary, uses C<sv_unref> and
upgrades the SV to C<SVt_PV>.  Returns a pointer to the character buffer.
Use the C<SvGROW> wrapper instead.

=cut
*/

char *
Perl_sv_grow(pTHX_ register SV *sv, register STRLEN newlen)
{
    register char *s;

    if (PL_madskills && newlen >= 0x100000) {
        PerlIO_printf(Perl_debug_log,
                      "Allocation too large: %"UVxf"\n", (UV)newlen);
    }
#ifdef HAS_64K_LIMIT
    if (newlen >= 0x10000) {
        PerlIO_printf(Perl_debug_log,
                      "Allocation too large: %"UVxf"\n", (UV)newlen);
        my_exit(1);
    }
#endif /* HAS_64K_LIMIT */
    if (SvROK(sv))
        sv_unref(sv);
    if (SvTYPE(sv) < SVt_PV) {
        sv_upgrade(sv, SVt_PV);
        s = SvPVX_mutable(sv);
    }
    else if (SvOOK(sv)) {       /* pv is offset? */
        sv_backoff(sv);
        s = SvPVX_mutable(sv);
        if (newlen > SvLEN(sv))
            newlen += 10 * (newlen - SvCUR(sv)); /* avoid copy each time */
#ifdef HAS_64K_LIMIT
        if (newlen >= 0x10000)
            newlen = 0xFFFF;
#endif
    }
    else
        s = SvPVX_mutable(sv);

    if (newlen > SvLEN(sv)) {           /* need more room? */
        newlen = PERL_STRLEN_ROUNDUP(newlen);
        if (SvLEN(sv) && s) {
#ifdef MYMALLOC
            const STRLEN l = malloced_size((void*)SvPVX_const(sv));
            if (newlen <= l) {
                SvLEN_set(sv, l);
                return s;
            } else
#endif
            s = (char*)saferealloc(s, newlen);
        }
        else {
            s = (char*)safemalloc(newlen);
            if (SvPVX_const(sv) && SvCUR(sv)) {
                Move(SvPVX_const(sv), s, (newlen < SvCUR(sv)) ? newlen : SvCUR(sv), char);
            }
        }
        SvPV_set(sv, s);
        SvLEN_set(sv, newlen);
    }
    return s;
}

/*
=for apidoc sv_setiv

Copies an integer into the given SV, upgrading first if necessary.
Does not handle 'set' magic.  See also C<sv_setiv_mg>.

=cut
*/

void
Perl_sv_setiv(pTHX_ register SV *sv, IV i)
{
    dVAR;
    SV_CHECK_THINKFIRST_COW_DROP(sv);
    switch (SvTYPE(sv)) {
    case SVt_NULL:
        sv_upgrade(sv, SVt_IV);
        break;
    case SVt_NV:
        sv_upgrade(sv, SVt_PVNV);
        break;
    case SVt_RV:
    case SVt_PV:
        sv_upgrade(sv, SVt_PVIV);
        break;

    case SVt_PVGV:
    case SVt_PVAV:
    case SVt_PVHV:
    case SVt_PVCV:
    case SVt_PVFM:
    case SVt_PVIO:
        Perl_croak(aTHX_ "Can't coerce %s to integer in %s", sv_reftype(sv,0),
                   OP_DESC(PL_op));
    default: NOOP;
    }
    (void)SvIOK_only(sv);                       /* validate number */
    SvIV_set(sv, i);
    SvTAINT(sv);
}

/*
=for apidoc sv_setiv_mg

Like C<sv_setiv>, but also handles 'set' magic.

=cut
*/

void
Perl_sv_setiv_mg(pTHX_ register SV *sv, IV i)
{
    sv_setiv(sv,i);
    SvSETMAGIC(sv);
}

/*
=for apidoc sv_setuv

Copies an unsigned integer into the given SV, upgrading first if necessary.
Does not handle 'set' magic.  See also C<sv_setuv_mg>.

=cut
*/

void
Perl_sv_setuv(pTHX_ register SV *sv, UV u)
{
    /* With these two if statements:
       u=1.49  s=0.52  cu=72.49  cs=10.64  scripts=270  tests=20865

       without
       u=1.35  s=0.47  cu=73.45  cs=11.43  scripts=270  tests=20865

       If you wish to remove them, please benchmark to see what the effect is
    */
    if (u <= (UV)IV_MAX) {
       sv_setiv(sv, (IV)u);
       return;
    }
    sv_setiv(sv, 0);
    SvIsUV_on(sv);
    SvUV_set(sv, u);
}

/*
=for apidoc sv_setuv_mg

Like C<sv_setuv>, but also handles 'set' magic.

=cut
*/

void
Perl_sv_setuv_mg(pTHX_ register SV *sv, UV u)
{
    sv_setuv(sv,u);
    SvSETMAGIC(sv);
}

/*
=for apidoc sv_setnv

Copies a double into the given SV, upgrading first if necessary.
Does not handle 'set' magic.  See also C<sv_setnv_mg>.

=cut
*/

void
Perl_sv_setnv(pTHX_ register SV *sv, NV num)
{
    dVAR;
    SV_CHECK_THINKFIRST_COW_DROP(sv);
    switch (SvTYPE(sv)) {
    case SVt_NULL:
    case SVt_IV:
        sv_upgrade(sv, SVt_NV);
        break;
    case SVt_RV:
    case SVt_PV:
    case SVt_PVIV:
        sv_upgrade(sv, SVt_PVNV);
        break;

    case SVt_PVGV:
    case SVt_PVAV:
    case SVt_PVHV:
    case SVt_PVCV:
    case SVt_PVFM:
    case SVt_PVIO:
        Perl_croak(aTHX_ "Can't coerce %s to number in %s", sv_reftype(sv,0),
                   OP_NAME(PL_op));
    default: NOOP;
    }
    SvNV_set(sv, num);
    (void)SvNOK_only(sv);                       /* validate number */
    SvTAINT(sv);
}

/*
=for apidoc sv_setnv_mg

Like C<sv_setnv>, but also handles 'set' magic.

=cut
*/

void
Perl_sv_setnv_mg(pTHX_ register SV *sv, NV num)
{
    sv_setnv(sv,num);
    SvSETMAGIC(sv);
}

/* Print an "isn't numeric" warning, using a cleaned-up,
 * printable version of the offending string
 */

STATIC void
S_not_a_number(pTHX_ SV *sv)
{
     dVAR;
     SV *dsv;
     char tmpbuf[64];
     const char *pv;

     if (DO_UTF8(sv)) {
          dsv = sv_2mortal(newSVpvs(""));
          pv = sv_uni_display(dsv, sv, 10, 0);
     } else {
          char *d = tmpbuf;
          const char * const limit = tmpbuf + sizeof(tmpbuf) - 8;
          /* each *s can expand to 4 chars + "...\0",
             i.e. need room for 8 chars */
        
          const char *s = SvPVX_const(sv);
          const char * const end = s + SvCUR(sv);
          for ( ; s < end && d < limit; s++ ) {
               int ch = *s & 0xFF;
               if (ch & 128 && !isPRINT_LC(ch)) {
                    *d++ = 'M';
                    *d++ = '-';
                    ch &= 127;
               }
               if (ch == '\n') {
                    *d++ = '\\';
                    *d++ = 'n';
               }
               else if (ch == '\r') {
                    *d++ = '\\';
                    *d++ = 'r';
               }
               else if (ch == '\f') {
                    *d++ = '\\';
                    *d++ = 'f';
               }
               else if (ch == '\\') {
                    *d++ = '\\';
                    *d++ = '\\';
               }
               else if (ch == '\0') {
                    *d++ = '\\';
                    *d++ = '0';
               }
               else if (isPRINT_LC(ch))
                    *d++ = ch;
               else {
                    *d++ = '^';
                    *d++ = toCTRL(ch);
               }
          }
          if (s < end) {
               *d++ = '.';
               *d++ = '.';
               *d++ = '.';
          }
          *d = '\0';
          pv = tmpbuf;
    }

    if (PL_op)
        Perl_warner(aTHX_ packWARN(WARN_NUMERIC),
                    "Argument \"%s\" isn't numeric in %s", pv,
                    OP_DESC(PL_op));
    else
        Perl_warner(aTHX_ packWARN(WARN_NUMERIC),
                    "Argument \"%s\" isn't numeric", pv);
}

/*
=for apidoc looks_like_number

Test if the content of an SV looks like a number (or is a number).
C<Inf> and C<Infinity> are treated as numbers (so will not issue a
non-numeric warning), even if your atof() doesn't grok them.

=cut
*/

I32
Perl_looks_like_number(pTHX_ SV *sv)
{
    register const char *sbegin;
    STRLEN len;

    if (SvPOK(sv)) {
        sbegin = SvPVX_const(sv);
        len = SvCUR(sv);
    }
    else if (SvPOKp(sv))
        sbegin = SvPV_const(sv, len);
    else
        return SvFLAGS(sv) & (SVf_NOK|SVp_NOK|SVf_IOK|SVp_IOK);
    return grok_number(sbegin, len, NULL);
}

STATIC bool
S_glob_2number(pTHX_ GV * const gv)
{
    const U32 wasfake = SvFLAGS(gv) & SVf_FAKE;
    SV *const buffer = sv_newmortal();

    /* FAKE globs can get coerced, so need to turn this off temporarily if it
       is on.  */
    SvFAKE_off(gv);
    gv_efullname3(buffer, gv, "*");
    SvFLAGS(gv) |= wasfake;

    /* We know that all GVs stringify to something that is not-a-number,
        so no need to test that.  */
    if (ckWARN(WARN_NUMERIC))
        not_a_number(buffer);
    /* We just want something true to return, so that S_sv_2iuv_common
        can tail call us and return true.  */
    return TRUE;
}

STATIC char *
S_glob_2pv(pTHX_ GV * const gv, STRLEN * const len)
{
    const U32 wasfake = SvFLAGS(gv) & SVf_FAKE;
    SV *const buffer = sv_newmortal();

    /* FAKE globs can get coerced, so need to turn this off temporarily if it
       is on.  */
    SvFAKE_off(gv);
    gv_efullname3(buffer, gv, "*");
    SvFLAGS(gv) |= wasfake;

    assert(SvPOK(buffer));
    if (len) {
        *len = SvCUR(buffer);
    }
    return SvPVX(buffer);
}

/* Actually, ISO C leaves conversion of UV to IV undefined, but
   until proven guilty, assume that things are not that bad... */

/*
   NV_PRESERVES_UV:

   As 64 bit platforms often have an NV that doesn't preserve all bits of
   an IV (an assumption perl has been based on to date) it becomes necessary
   to remove the assumption that the NV always carries enough precision to
   recreate the IV whenever needed, and that the NV is the canonical form.
   Instead, IV/UV and NV need to be given equal rights. So as to not lose
   precision as a side effect of conversion (which would lead to insanity
   and the dragon(s) in t/op/numconvert.t getting very angry) the intent is
   1) to distinguish between IV/UV/NV slots that have cached a valid
      conversion where precision was lost and IV/UV/NV slots that have a
      valid conversion which has lost no precision
   2) to ensure that if a numeric conversion to one form is requested that
      would lose precision, the precise conversion (or differently
      imprecise conversion) is also performed and cached, to prevent
      requests for different numeric formats on the same SV causing
      lossy conversion chains. (lossless conversion chains are perfectly
      acceptable (still))


   flags are used:
   SvIOKp is true if the IV slot contains a valid value
   SvIOK  is true only if the IV value is accurate (UV if SvIOK_UV true)
   SvNOKp is true if the NV slot contains a valid value
   SvNOK  is true only if the NV value is accurate

   so
   while converting from PV to NV, check to see if converting that NV to an
   IV(or UV) would lose accuracy over a direct conversion from PV to
   IV(or UV). If it would, cache both conversions, return NV, but mark
   SV as IOK NOKp (ie not NOK).

   While converting from PV to IV, check to see if converting that IV to an
   NV would lose accuracy over a direct conversion from PV to NV. If it
   would, cache both conversions, flag similarly.

   Before, the SV value "3.2" could become NV=3.2 IV=3 NOK, IOK quite
   correctly because if IV & NV were set NV *always* overruled.
   Now, "3.2" will become NV=3.2 IV=3 NOK, IOKp, because the flag's meaning
   changes - now IV and NV together means that the two are interchangeable:
   SvIVX == (IV) SvNVX && SvNVX == (NV) SvIVX;

   The benefit of this is that operations such as pp_add know that if
   SvIOK is true for both left and right operands, then integer addition
   can be used instead of floating point (for cases where the result won't
   overflow). Before, floating point was always used, which could lead to
   loss of precision compared with integer addition.

   * making IV and NV equal status should make maths accurate on 64 bit
     platforms
   * may speed up maths somewhat if pp_add and friends start to use
     integers when possible instead of fp. (Hopefully the overhead in
     looking for SvIOK and checking for overflow will not outweigh the
     fp to integer speedup)
   * will slow down integer operations (callers of SvIV) on "inaccurate"
     values, as the change from SvIOK to SvIOKp will cause a call into
     sv_2iv each time rather than a macro access direct to the IV slot
   * should speed up number->string conversion on integers as IV is
     favoured when IV and NV are equally accurate

   ####################################################################
   You had better be using SvIOK_notUV if you want an IV for arithmetic:
   SvIOK is true if (IV or UV), so you might be getting (IV)SvUV.
   On the other hand, SvUOK is true iff UV.
   ####################################################################

   Your mileage will vary depending your CPU's relative fp to integer
   performance ratio.
*/

#ifndef NV_PRESERVES_UV
#  define IS_NUMBER_UNDERFLOW_IV 1
#  define IS_NUMBER_UNDERFLOW_UV 2
#  define IS_NUMBER_IV_AND_UV    2
#  define IS_NUMBER_OVERFLOW_IV  4
#  define IS_NUMBER_OVERFLOW_UV  5

/* sv_2iuv_non_preserve(): private routine for use by sv_2iv() and sv_2uv() */

/* For sv_2nv these three cases are "SvNOK and don't bother casting"  */
STATIC int
S_sv_2iuv_non_preserve(pTHX_ register SV *sv, I32 numtype)
{
    dVAR;
    PERL_UNUSED_ARG(numtype); /* Used only under DEBUGGING? */
    DEBUG_c(PerlIO_printf(Perl_debug_log,"sv_2iuv_non '%s', IV=0x%"UVxf" NV=%"NVgf" inttype=%"UVXf"\n", SvPVX_const(sv), SvIVX(sv), SvNVX(sv), (UV)numtype));
    if (SvNVX(sv) < (NV)IV_MIN) {
        (void)SvIOKp_on(sv);
        (void)SvNOK_on(sv);
        SvIV_set(sv, IV_MIN);
        return IS_NUMBER_UNDERFLOW_IV;
    }
    if (SvNVX(sv) > (NV)UV_MAX) {
        (void)SvIOKp_on(sv);
        (void)SvNOK_on(sv);
        SvIsUV_on(sv);
        SvUV_set(sv, UV_MAX);
        return IS_NUMBER_OVERFLOW_UV;
    }
    (void)SvIOKp_on(sv);
    (void)SvNOK_on(sv);
    /* Can't use strtol etc to convert this string.  (See truth table in
       sv_2iv  */
    if (SvNVX(sv) <= (UV)IV_MAX) {
        SvIV_set(sv, I_V(SvNVX(sv)));
        if ((NV)(SvIVX(sv)) == SvNVX(sv)) {
            SvIOK_on(sv); /* Integer is precise. NOK, IOK */
        } else {
            /* Integer is imprecise. NOK, IOKp */
        }
        return SvNVX(sv) < 0 ? IS_NUMBER_UNDERFLOW_UV : IS_NUMBER_IV_AND_UV;
    }
    SvIsUV_on(sv);
    SvUV_set(sv, U_V(SvNVX(sv)));
    if ((NV)(SvUVX(sv)) == SvNVX(sv)) {
        if (SvUVX(sv) == UV_MAX) {
            /* As we know that NVs don't preserve UVs, UV_MAX cannot
               possibly be preserved by NV. Hence, it must be overflow.
               NOK, IOKp */
            return IS_NUMBER_OVERFLOW_UV;
        }
        SvIOK_on(sv); /* Integer is precise. NOK, UOK */
    } else {
        /* Integer is imprecise. NOK, IOKp */
    }
    return IS_NUMBER_OVERFLOW_IV;
}
#endif /* !NV_PRESERVES_UV*/

STATIC bool
S_sv_2iuv_common(pTHX_ SV *sv) {
    dVAR;
    if (SvNOKp(sv)) {
        /* erm. not sure. *should* never get NOKp (without NOK) from sv_2nv
         * without also getting a cached IV/UV from it at the same time
         * (ie PV->NV conversion should detect loss of accuracy and cache
         * IV or UV at same time to avoid this. */
        /* IV-over-UV optimisation - choose to cache IV if possible */

        if (SvTYPE(sv) == SVt_NV)
            sv_upgrade(sv, SVt_PVNV);

        (void)SvIOKp_on(sv);    /* Must do this first, to clear any SvOOK */
        /* < not <= as for NV doesn't preserve UV, ((NV)IV_MAX+1) will almost
           certainly cast into the IV range at IV_MAX, whereas the correct
           answer is the UV IV_MAX +1. Hence < ensures that dodgy boundary
           cases go to UV */
#if defined(NAN_COMPARE_BROKEN) && defined(Perl_isnan)
        if (Perl_isnan(SvNVX(sv))) {
            SvUV_set(sv, 0);
            SvIsUV_on(sv);
            return FALSE;
        }
#endif
        if (SvNVX(sv) < (NV)IV_MAX + 0.5) {
            SvIV_set(sv, I_V(SvNVX(sv)));
            if (SvNVX(sv) == (NV) SvIVX(sv)
#ifndef NV_PRESERVES_UV
                && (((UV)1 << NV_PRESERVES_UV_BITS) >
                    (UV)(SvIVX(sv) > 0 ? SvIVX(sv) : -SvIVX(sv)))
                /* Don't flag it as "accurately an integer" if the number
                   came from a (by definition imprecise) NV operation, and
                   we're outside the range of NV integer precision */
#endif
                ) {
                SvIOK_on(sv);  /* Can this go wrong with rounding? NWC */
                DEBUG_c(PerlIO_printf(Perl_debug_log,
                                      "0x%"UVxf" iv(%"NVgf" => %"IVdf") (precise)\n",
                                      PTR2UV(sv),
                                      SvNVX(sv),
                                      SvIVX(sv)));

            } else {
                /* IV not precise.  No need to convert from PV, as NV
                   conversion would already have cached IV if it detected
                   that PV->IV would be better than PV->NV->IV
                   flags already correct - don't set public IOK.  */
                DEBUG_c(PerlIO_printf(Perl_debug_log,
                                      "0x%"UVxf" iv(%"NVgf" => %"IVdf") (imprecise)\n",
                                      PTR2UV(sv),
                                      SvNVX(sv),
                                      SvIVX(sv)));
            }
            /* Can the above go wrong if SvIVX == IV_MIN and SvNVX < IV_MIN,
               but the cast (NV)IV_MIN rounds to a the value less (more
               negative) than IV_MIN which happens to be equal to SvNVX ??
               Analogous to 0xFFFFFFFFFFFFFFFF rounding up to NV (2**64) and
               NV rounding back to 0xFFFFFFFFFFFFFFFF, so UVX == UV(NVX) and
               (NV)UVX == NVX are both true, but the values differ. :-(
               Hopefully for 2s complement IV_MIN is something like
               0x8000000000000000 which will be exact. NWC */
        }
        else {
            SvUV_set(sv, U_V(SvNVX(sv)));
            if (
                (SvNVX(sv) == (NV) SvUVX(sv))
#ifndef  NV_PRESERVES_UV
                /* Make sure it's not 0xFFFFFFFFFFFFFFFF */
                /*&& (SvUVX(sv) != UV_MAX) irrelevant with code below */
                && (((UV)1 << NV_PRESERVES_UV_BITS) > SvUVX(sv))
                /* Don't flag it as "accurately an integer" if the number
                   came from a (by definition imprecise) NV operation, and
                   we're outside the range of NV integer precision */
#endif
                )
                SvIOK_on(sv);
            SvIsUV_on(sv);
            DEBUG_c(PerlIO_printf(Perl_debug_log,
                                  "0x%"UVxf" 2iv(%"UVuf" => %"IVdf") (as unsigned)\n",
                                  PTR2UV(sv),
                                  SvUVX(sv),
                                  SvUVX(sv)));
        }
    }
    else if (SvPOKp(sv) && SvLEN(sv)) {
        UV value;
        const int numtype = grok_number(SvPVX_const(sv), SvCUR(sv), &value);
        /* We want to avoid a possible problem when we cache an IV/ a UV which
           may be later translated to an NV, and the resulting NV is not
           the same as the direct translation of the initial string
           (eg 123.456 can shortcut to the IV 123 with atol(), but we must
           be careful to ensure that the value with the .456 is around if the
           NV value is requested in the future).
        
           This means that if we cache such an IV/a UV, we need to cache the
           NV as well.  Moreover, we trade speed for space, and do not
           cache the NV if we are sure it's not needed.
         */

        /* SVt_PVNV is one higher than SVt_PVIV, hence this order  */
        if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
             == IS_NUMBER_IN_UV) {
            /* It's definitely an integer, only upgrade to PVIV */
            if (SvTYPE(sv) < SVt_PVIV)
                sv_upgrade(sv, SVt_PVIV);
            (void)SvIOK_on(sv);
        } else if (SvTYPE(sv) < SVt_PVNV)
            sv_upgrade(sv, SVt_PVNV);

        /* If NVs preserve UVs then we only use the UV value if we know that
           we aren't going to call atof() below. If NVs don't preserve UVs
           then the value returned may have more precision than atof() will
           return, even though value isn't perfectly accurate.  */
        if ((numtype & (IS_NUMBER_IN_UV
#ifdef NV_PRESERVES_UV
                        | IS_NUMBER_NOT_INT
#endif
            )) == IS_NUMBER_IN_UV) {
            /* This won't turn off the public IOK flag if it was set above  */
            (void)SvIOKp_on(sv);

            if (!(numtype & IS_NUMBER_NEG)) {
                /* positive */;
                if (value <= (UV)IV_MAX) {
                    SvIV_set(sv, (IV)value);
                } else {
                    /* it didn't overflow, and it was positive. */
                    SvUV_set(sv, value);
                    SvIsUV_on(sv);
                }
            } else {
                /* 2s complement assumption  */
                if (value <= (UV)IV_MIN) {
                    SvIV_set(sv, -(IV)value);
                } else {
                    /* Too negative for an IV.  This is a double upgrade, but
                       I'm assuming it will be rare.  */
                    if (SvTYPE(sv) < SVt_PVNV)
                        sv_upgrade(sv, SVt_PVNV);
                    SvNOK_on(sv);
                    SvIOK_off(sv);
                    SvIOKp_on(sv);
                    SvNV_set(sv, -(NV)value);
                    SvIV_set(sv, IV_MIN);
                }
            }
        }
        /* For !NV_PRESERVES_UV and IS_NUMBER_IN_UV and IS_NUMBER_NOT_INT we
           will be in the previous block to set the IV slot, and the next
           block to set the NV slot.  So no else here.  */
        
        if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
            != IS_NUMBER_IN_UV) {
            /* It wasn't an (integer that doesn't overflow the UV). */
            SvNV_set(sv, Atof(SvPVX_const(sv)));

            if (! numtype && ckWARN(WARN_NUMERIC))
                not_a_number(sv);

#if defined(USE_LONG_DOUBLE)
            DEBUG_c(PerlIO_printf(Perl_debug_log, "0x%"UVxf" 2iv(%" PERL_PRIgldbl ")\n",
                                  PTR2UV(sv), SvNVX(sv)));
#else
            DEBUG_c(PerlIO_printf(Perl_debug_log, "0x%"UVxf" 2iv(%"NVgf")\n",
                                  PTR2UV(sv), SvNVX(sv)));
#endif

#ifdef NV_PRESERVES_UV
            (void)SvIOKp_on(sv);
            (void)SvNOK_on(sv);
            if (SvNVX(sv) < (NV)IV_MAX + 0.5) {
                SvIV_set(sv, I_V(SvNVX(sv)));
                if ((NV)(SvIVX(sv)) == SvNVX(sv)) {
                    SvIOK_on(sv);
                } else {
                    NOOP;  /* Integer is imprecise. NOK, IOKp */
                }
                /* UV will not work better than IV */
            } else {
                if (SvNVX(sv) > (NV)UV_MAX) {
                    SvIsUV_on(sv);
                    /* Integer is inaccurate. NOK, IOKp, is UV */
                    SvUV_set(sv, UV_MAX);
                } else {
                    SvUV_set(sv, U_V(SvNVX(sv)));
                    /* 0xFFFFFFFFFFFFFFFF not an issue in here, NVs
                       NV preservse UV so can do correct comparison.  */
                    if ((NV)(SvUVX(sv)) == SvNVX(sv)) {
                        SvIOK_on(sv);
                    } else {
                        NOOP;   /* Integer is imprecise. NOK, IOKp, is UV */
                    }
                }
                SvIsUV_on(sv);
            }
#else /* NV_PRESERVES_UV */
            if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
                == (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT)) {
                /* The IV/UV slot will have been set from value returned by
                   grok_number above.  The NV slot has just been set using
                   Atof.  */
                SvNOK_on(sv);
                assert (SvIOKp(sv));
            } else {
                if (((UV)1 << NV_PRESERVES_UV_BITS) >
                    U_V(SvNVX(sv) > 0 ? SvNVX(sv) : -SvNVX(sv))) {
                    /* Small enough to preserve all bits. */
                    (void)SvIOKp_on(sv);
                    SvNOK_on(sv);
                    SvIV_set(sv, I_V(SvNVX(sv)));
                    if ((NV)(SvIVX(sv)) == SvNVX(sv))
                        SvIOK_on(sv);
                    /* Assumption: first non-preserved integer is < IV_MAX,
                       this NV is in the preserved range, therefore: */
                    if (!(U_V(SvNVX(sv) > 0 ? SvNVX(sv) : -SvNVX(sv))
                          < (UV)IV_MAX)) {
                        Perl_croak(aTHX_ "sv_2iv assumed (U_V(fabs((double)SvNVX(sv))) < (UV)IV_MAX) but SvNVX(sv)=%"NVgf" U_V is 0x%"UVxf", IV_MAX is 0x%"UVxf"\n", SvNVX(sv), U_V(SvNVX(sv)), (UV)IV_MAX);
                    }
                } else {
                    /* IN_UV NOT_INT
                         0      0       already failed to read UV.
                         0      1       already failed to read UV.
                         1      0       you won't get here in this case. IV/UV
                                        slot set, public IOK, Atof() unneeded.
                         1      1       already read UV.
                       so there's no point in sv_2iuv_non_preserve() attempting
                       to use atol, strtol, strtoul etc.  */
                    sv_2iuv_non_preserve (sv, numtype);
                }
            }
#endif /* NV_PRESERVES_UV */
        }
    }
    else  {
        if (isGV_with_GP(sv))
            return glob_2number((GV *)sv);

        if (!(SvFLAGS(sv) & SVs_PADTMP)) {
            if (!PL_localizing && ckWARN(WARN_UNINITIALIZED))
                report_uninit(sv);
        }
        if (SvTYPE(sv) < SVt_IV)
            /* Typically the caller expects that sv_any is not NULL now.  */
            sv_upgrade(sv, SVt_IV);
        /* Return 0 from the caller.  */
        return TRUE;
    }
    return FALSE;
}

/*
=for apidoc sv_2iv_flags

Return the integer value of an SV, doing any necessary string
conversion.  If flags includes SV_GMAGIC, does an mg_get() first.
Normally used via the C<SvIV(sv)> and C<SvIVx(sv)> macros.

=cut
*/

IV
Perl_sv_2iv_flags(pTHX_ register SV *sv, I32 flags)
{
    dVAR;
    if (!sv)
        return 0;
    if (SvGMAGICAL(sv) || (SvTYPE(sv) == SVt_PVGV && SvVALID(sv))) {
        /* FBMs use the same flag bit as SVf_IVisUV, so must let them
           cache IVs just in case. In practice it seems that they never
           actually anywhere accessible by user Perl code, let alone get used
           in anything other than a string context.  */
        if (flags & SV_GMAGIC)
            mg_get(sv);
        if (SvIOKp(sv))
            return SvIVX(sv);
        if (SvNOKp(sv)) {
            return I_V(SvNVX(sv));
        }
        if (SvPOKp(sv) && SvLEN(sv)) {
            UV value;
            const int numtype
                = grok_number(SvPVX_const(sv), SvCUR(sv), &value);

            if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
                == IS_NUMBER_IN_UV) {
                /* It's definitely an integer */
                if (numtype & IS_NUMBER_NEG) {
                    if (value < (UV)IV_MIN)
                        return -(IV)value;
                } else {
                    if (value < (UV)IV_MAX)
                        return (IV)value;
                }
            }
            if (!numtype) {
                if (ckWARN(WARN_NUMERIC))
                    not_a_number(sv);
            }
            return I_V(Atof(SvPVX_const(sv)));
        }
        if (SvROK(sv)) {
            goto return_rok;
        }
        assert(SvTYPE(sv) >= SVt_PVMG);
        /* This falls through to the report_uninit inside S_sv_2iuv_common.  */
    } else if (SvTHINKFIRST(sv)) {
        if (SvROK(sv)) {
        return_rok:
            if (SvAMAGIC(sv)) {
                SV * const tmpstr=AMG_CALLun(sv,numer);
                if (tmpstr && (!SvROK(tmpstr) || (SvRV(tmpstr) != SvRV(sv)))) {
                    return SvIV(tmpstr);
                }
            }
            return PTR2IV(SvRV(sv));
        }
        if (SvIsCOW(sv)) {
            sv_force_normal_flags(sv, 0);
        }
        if (SvREADONLY(sv) && !SvOK(sv)) {
            if (ckWARN(WARN_UNINITIALIZED))
                report_uninit(sv);
            return 0;
        }
    }
    if (!SvIOKp(sv)) {
        if (S_sv_2iuv_common(aTHX_ sv))
            return 0;
    }
    DEBUG_c(PerlIO_printf(Perl_debug_log, "0x%"UVxf" 2iv(%"IVdf")\n",
        PTR2UV(sv),SvIVX(sv)));
    return SvIsUV(sv) ? (IV)SvUVX(sv) : SvIVX(sv);
}

/*
=for apidoc sv_2uv_flags

Return the unsigned integer value of an SV, doing any necessary string
conversion.  If flags includes SV_GMAGIC, does an mg_get() first.
Normally used via the C<SvUV(sv)> and C<SvUVx(sv)> macros.

=cut
*/

UV
Perl_sv_2uv_flags(pTHX_ register SV *sv, I32 flags)
{
    dVAR;
    if (!sv)
        return 0;
    if (SvGMAGICAL(sv) || (SvTYPE(sv) == SVt_PVGV && SvVALID(sv))) {
        /* FBMs use the same flag bit as SVf_IVisUV, so must let them
           cache IVs just in case.  */
        if (flags & SV_GMAGIC)
            mg_get(sv);
        if (SvIOKp(sv))
            return SvUVX(sv);
        if (SvNOKp(sv))
            return U_V(SvNVX(sv));
        if (SvPOKp(sv) && SvLEN(sv)) {
            UV value;
            const int numtype
                = grok_number(SvPVX_const(sv), SvCUR(sv), &value);

            if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
                == IS_NUMBER_IN_UV) {
                /* It's definitely an integer */
                if (!(numtype & IS_NUMBER_NEG))
                    return value;
            }
            if (!numtype) {
                if (ckWARN(WARN_NUMERIC))
                    not_a_number(sv);
            }
            return U_V(Atof(SvPVX_const(sv)));
        }
        if (SvROK(sv)) {
            goto return_rok;
        }
        assert(SvTYPE(sv) >= SVt_PVMG);
        /* This falls through to the report_uninit inside S_sv_2iuv_common.  */
    } else if (SvTHINKFIRST(sv)) {
        if (SvROK(sv)) {
        return_rok:
            if (SvAMAGIC(sv)) {
                SV *const tmpstr = AMG_CALLun(sv,numer);
                if (tmpstr && (!SvROK(tmpstr) || (SvRV(tmpstr) != SvRV(sv)))) {
                    return SvUV(tmpstr);
                }
            }
            return PTR2UV(SvRV(sv));
        }
        if (SvIsCOW(sv)) {
            sv_force_normal_flags(sv, 0);
        }
        if (SvREADONLY(sv) && !SvOK(sv)) {
            if (ckWARN(WARN_UNINITIALIZED))
                report_uninit(sv);
            return 0;
        }
    }
    if (!SvIOKp(sv)) {
        if (S_sv_2iuv_common(aTHX_ sv))
            return 0;
    }

    DEBUG_c(PerlIO_printf(Perl_debug_log, "0x%"UVxf" 2uv(%"UVuf")\n",
                          PTR2UV(sv),SvUVX(sv)));
    return SvIsUV(sv) ? SvUVX(sv) : (UV)SvIVX(sv);
}

/*
=for apidoc sv_2nv

Return the num value of an SV, doing any necessary string or integer
conversion, magic etc. Normally used via the C<SvNV(sv)> and C<SvNVx(sv)>
macros.

=cut
*/

NV
Perl_sv_2nv(pTHX_ register SV *sv)
{
    dVAR;
    if (!sv)
        return 0.0;
    if (SvGMAGICAL(sv) || (SvTYPE(sv) == SVt_PVGV && SvVALID(sv))) {
        /* FBMs use the same flag bit as SVf_IVisUV, so must let them
           cache IVs just in case.  */
        mg_get(sv);
        if (SvNOKp(sv))
            return SvNVX(sv);
        if ((SvPOKp(sv) && SvLEN(sv)) && !SvIOKp(sv)) {
            if (!SvIOKp(sv) && ckWARN(WARN_NUMERIC) &&
                !grok_number(SvPVX_const(sv), SvCUR(sv), NULL))
                not_a_number(sv);
            return Atof(SvPVX_const(sv));
        }
        if (SvIOKp(sv)) {
            if (SvIsUV(sv))
                return (NV)SvUVX(sv);
            else
                return (NV)SvIVX(sv);
        }
        if (SvROK(sv)) {
            goto return_rok;
        }
        assert(SvTYPE(sv) >= SVt_PVMG);
        /* This falls through to the report_uninit near the end of the
           function. */
    } else if (SvTHINKFIRST(sv)) {
        if (SvROK(sv)) {
        return_rok:
            if (SvAMAGIC(sv)) {
                SV *const tmpstr = AMG_CALLun(sv,numer);
                if (tmpstr && (!SvROK(tmpstr) || (SvRV(tmpstr) != SvRV(sv)))) {
                    return SvNV(tmpstr);
                }
            }
            return PTR2NV(SvRV(sv));
        }
        if (SvIsCOW(sv)) {
            sv_force_normal_flags(sv, 0);
        }
        if (SvREADONLY(sv) && !SvOK(sv)) {
            if (ckWARN(WARN_UNINITIALIZED))
                report_uninit(sv);
            return 0.0;
        }
    }
    if (SvTYPE(sv) < SVt_NV) {
        /* The logic to use SVt_PVNV if necessary is in sv_upgrade.  */
        sv_upgrade(sv, SVt_NV);
#ifdef USE_LONG_DOUBLE
        DEBUG_c({
            STORE_NUMERIC_LOCAL_SET_STANDARD();
            PerlIO_printf(Perl_debug_log,
                          "0x%"UVxf" num(%" PERL_PRIgldbl ")\n",
                          PTR2UV(sv), SvNVX(sv));
            RESTORE_NUMERIC_LOCAL();
        });
#else
        DEBUG_c({
            STORE_NUMERIC_LOCAL_SET_STANDARD();
            PerlIO_printf(Perl_debug_log, "0x%"UVxf" num(%"NVgf")\n",
                          PTR2UV(sv), SvNVX(sv));
            RESTORE_NUMERIC_LOCAL();
        });
#endif
    }
    else if (SvTYPE(sv) < SVt_PVNV)
        sv_upgrade(sv, SVt_PVNV);
    if (SvNOKp(sv)) {
        return SvNVX(sv);
    }
    if (SvIOKp(sv)) {
        SvNV_set(sv, SvIsUV(sv) ? (NV)SvUVX(sv) : (NV)SvIVX(sv));
#ifdef NV_PRESERVES_UV
        SvNOK_on(sv);
#else
        /* Only set the public NV OK flag if this NV preserves the IV  */
        /* Check it's not 0xFFFFFFFFFFFFFFFF */
        if (SvIsUV(sv) ? ((SvUVX(sv) != UV_MAX)&&(SvUVX(sv) == U_V(SvNVX(sv))))
                       : (SvIVX(sv) == I_V(SvNVX(sv))))
            SvNOK_on(sv);
        else
            SvNOKp_on(sv);
#endif
    }
    else if (SvPOKp(sv) && SvLEN(sv)) {
        UV value;
        const int numtype = grok_number(SvPVX_const(sv), SvCUR(sv), &value);
        if (!SvIOKp(sv) && !numtype && ckWARN(WARN_NUMERIC))
            not_a_number(sv);
#ifdef NV_PRESERVES_UV
        if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
            == IS_NUMBER_IN_UV) {
            /* It's definitely an integer */
            SvNV_set(sv, (numtype & IS_NUMBER_NEG) ? -(NV)value : (NV)value);
        } else
            SvNV_set(sv, Atof(SvPVX_const(sv)));
        SvNOK_on(sv);
#else
        SvNV_set(sv, Atof(SvPVX_const(sv)));
        /* Only set the public NV OK flag if this NV preserves the value in
           the PV at least as well as an IV/UV would.
           Not sure how to do this 100% reliably. */
        /* if that shift count is out of range then Configure's test is
           wonky. We shouldn't be in here with NV_PRESERVES_UV_BITS ==
           UV_BITS */
        if (((UV)1 << NV_PRESERVES_UV_BITS) >
            U_V(SvNVX(sv) > 0 ? SvNVX(sv) : -SvNVX(sv))) {
            SvNOK_on(sv); /* Definitely small enough to preserve all bits */
        } else if (!(numtype & IS_NUMBER_IN_UV)) {
            /* Can't use strtol etc to convert this string, so don't try.
               sv_2iv and sv_2uv will use the NV to convert, not the PV.  */
            SvNOK_on(sv);
        } else {
            /* value has been set.  It may not be precise.  */
            if ((numtype & IS_NUMBER_NEG) && (value > (UV)IV_MIN)) {
                /* 2s complement assumption for (UV)IV_MIN  */
                SvNOK_on(sv); /* Integer is too negative.  */
            } else {
                SvNOKp_on(sv);
                SvIOKp_on(sv);

                if (numtype & IS_NUMBER_NEG) {
                    SvIV_set(sv, -(IV)value);
                } else if (value <= (UV)IV_MAX) {
                    SvIV_set(sv, (IV)value);
                } else {
                    SvUV_set(sv, value);
                    SvIsUV_on(sv);
                }

                if (numtype & IS_NUMBER_NOT_INT) {
                    /* I believe that even if the original PV had decimals,
                       they are lost beyond the limit of the FP precision.
                       However, neither is canonical, so both only get p
                       flags.  NWC, 2000/11/25 */
                    /* Both already have p flags, so do nothing */
                } else {
                    const NV nv = SvNVX(sv);
                    if (SvNVX(sv) < (NV)IV_MAX + 0.5) {
                        if (SvIVX(sv) == I_V(nv)) {
                            SvNOK_on(sv);
                        } else {
                            /* It had no "." so it must be integer.  */
                        }
                        SvIOK_on(sv);
                    } else {
                        /* between IV_MAX and NV(UV_MAX).
                           Could be slightly > UV_MAX */

                        if (numtype & IS_NUMBER_NOT_INT) {
                            /* UV and NV both imprecise.  */
                        } else {
                            const UV nv_as_uv = U_V(nv);

                            if (value == nv_as_uv && SvUVX(sv) != UV_MAX) {
                                SvNOK_on(sv);
                            }
                            SvIOK_on(sv);
                        }
                    }
                }
            }
        }
#endif /* NV_PRESERVES_UV */
    }
    else  {
        if (isGV_with_GP(sv)) {
            glob_2number((GV *)sv);
            return 0.0;
        }

        if (!PL_localizing && !(SvFLAGS(sv) & SVs_PADTMP) && ckWARN(WARN_UNINITIALIZED))
            report_uninit(sv);
        assert (SvTYPE(sv) >= SVt_NV);
        /* Typically the caller expects that sv_any is not NULL now.  */
        /* XXX Ilya implies that this is a bug in callers that assume this
           and ideally should be fixed.  */
        return 0.0;
    }
#if defined(USE_LONG_DOUBLE)
    DEBUG_c({
        STORE_NUMERIC_LOCAL_SET_STANDARD();
        PerlIO_printf(Perl_debug_log, "0x%"UVxf" 2nv(%" PERL_PRIgldbl ")\n",
                      PTR2UV(sv), SvNVX(sv));
        RESTORE_NUMERIC_LOCAL();
    });
#else
    DEBUG_c({
        STORE_NUMERIC_LOCAL_SET_STANDARD();
        PerlIO_printf(Perl_debug_log, "0x%"UVxf" 1nv(%"NVgf")\n",
                      PTR2UV(sv), SvNVX(sv));
        RESTORE_NUMERIC_LOCAL();
    });
#endif
    return SvNVX(sv);
}

/* uiv_2buf(): private routine for use by sv_2pv_flags(): print an IV or
 * UV as a string towards the end of buf, and return pointers to start and
 * end of it.
 *
 * We assume that buf is at least TYPE_CHARS(UV) long.
 */

static char *
S_uiv_2buf(char *buf, IV iv, UV uv, int is_uv, char **peob)
{
    char *ptr = buf + TYPE_CHARS(UV);
    char * const ebuf = ptr;
    int sign;

    if (is_uv)
        sign = 0;
    else if (iv >= 0) {
        uv = iv;
        sign = 0;
    } else {
        uv = -iv;
        sign = 1;
    }
    do {
        *--ptr = '0' + (char)(uv % 10);
    } while (uv /= 10);
    if (sign)
        *--ptr = '-';
    *peob = ebuf;
    return ptr;
}

/*
=for apidoc sv_2pv_flags

Returns a pointer to the string value of an SV, and sets *lp to its length.
If flags includes SV_GMAGIC, does an mg_get() first. Coerces sv to a string
if necessary.
Normally invoked via the C<SvPV_flags> macro. C<sv_2pv()> and C<sv_2pv_nomg>
usually end up here too.

=cut
*/

char *
Perl_sv_2pv_flags(pTHX_ register SV *sv, STRLEN *lp, I32 flags)
{
    dVAR;
    register char *s;

    if (!sv) {
        if (lp)
            *lp = 0;
        return (char *)"";
    }
    if (SvGMAGICAL(sv)) {
        if (flags & SV_GMAGIC)
            mg_get(sv);
        if (SvPOKp(sv)) {
            if (lp)
                *lp = SvCUR(sv);
            if (flags & SV_MUTABLE_RETURN)
                return SvPVX_mutable(sv);
            if (flags & SV_CONST_RETURN)
                return (char *)SvPVX_const(sv);
            return SvPVX(sv);
        }
        if (SvIOKp(sv) || SvNOKp(sv)) {
            char tbuf[64];  /* Must fit sprintf/Gconvert of longest IV/NV */
            STRLEN len;

            if (SvIOKp(sv)) {
                len = SvIsUV(sv)
                    ? my_snprintf(tbuf, sizeof(tbuf), "%"UVuf, (UV)SvUVX(sv))
                    : my_snprintf(tbuf, sizeof(tbuf), "%"IVdf, (IV)SvIVX(sv));
            } else {
                Gconvert(SvNVX(sv), NV_DIG, 0, tbuf);
                len = strlen(tbuf);
            }
            assert(!SvROK(sv));
            {
                dVAR;

#ifdef FIXNEGATIVEZERO
                if (len == 2 && tbuf[0] == '-' && tbuf[1] == '0') {
                    tbuf[0] = '0';
                    tbuf[1] = 0;
                    len = 1;
                }
#endif
                SvUPGRADE(sv, SVt_PV);
                if (lp)
                    *lp = len;
                s = SvGROW_mutable(sv, len + 1);
                SvCUR_set(sv, len);
                SvPOKp_on(sv);
                return (char*)memcpy(s, tbuf, len + 1);
            }
        }
        if (SvROK(sv)) {
            goto return_rok;
        }
        assert(SvTYPE(sv) >= SVt_PVMG);
        /* This falls through to the report_uninit near the end of the
           function. */
    } else if (SvTHINKFIRST(sv)) {
        if (SvROK(sv)) {
        return_rok:
            if (SvAMAGIC(sv)) {
                SV *const tmpstr = AMG_CALLun(sv,string);
                if (tmpstr && (!SvROK(tmpstr) || (SvRV(tmpstr) != SvRV(sv)))) {
                    /* Unwrap this:  */
                    /* char *pv = lp ? SvPV(tmpstr, *lp) : SvPV_nolen(tmpstr);
                     */

                    char *pv;
                    if ((SvFLAGS(tmpstr) & (SVf_POK)) == SVf_POK) {
                        if (flags & SV_CONST_RETURN) {
                            pv = (char *) SvPVX_const(tmpstr);
                        } else {
                            pv = (flags & SV_MUTABLE_RETURN)
                                ? SvPVX_mutable(tmpstr) : SvPVX(tmpstr);
                        }
                        if (lp)
                            *lp = SvCUR(tmpstr);
                    } else {
                        pv = sv_2pv_flags(tmpstr, lp, flags);
                    }
                    if (SvUTF8(tmpstr))
                        SvUTF8_on(sv);
                    else
                        SvUTF8_off(sv);
                    return pv;
                }
            }
            {
                STRLEN len;
                char *retval;
                char *buffer;
                MAGIC *mg;
                const SV *const referent = (SV*)SvRV(sv);

                if (!referent) {
                    len = 7;
                    retval = buffer = savepvn("NULLREF", len);
                } else if (SvTYPE(referent) == SVt_PVMG
                           && ((SvFLAGS(referent) &
                                (SVs_OBJECT|SVf_OK|SVs_GMG|SVs_SMG|SVs_RMG))
                               == (SVs_OBJECT|SVs_SMG))
                           && (mg = mg_find(referent, PERL_MAGIC_qr)))
                {
                    char *str = NULL;
                    I32 haseval = 0;
                    U32 flags = 0;
                    (str) = CALLREG_AS_STR(mg,lp,&flags,&haseval);
                    if (flags & 1)
                        SvUTF8_on(sv);
                    else
                        SvUTF8_off(sv);
                    PL_reginterp_cnt += haseval;
                    return str;
                } else {
                    const char *const typestr = sv_reftype(referent, 0);
                    const STRLEN typelen = strlen(typestr);
                    UV addr = PTR2UV(referent);
                    const char *stashname = NULL;
                    STRLEN stashnamelen = 0; /* hush, gcc */
                    const char *buffer_end;

                    if (SvOBJECT(referent)) {
                        const HEK *const name = HvNAME_HEK(SvSTASH(referent));

                        if (name) {
                            stashname = HEK_KEY(name);
                            stashnamelen = HEK_LEN(name);

                            if (HEK_UTF8(name)) {
                                SvUTF8_on(sv);
                            } else {
                                SvUTF8_off(sv);
                            }
                        } else {
                            stashname = "__ANON__";
                            stashnamelen = 8;
                        }
                        len = stashnamelen + 1 /* = */ + typelen + 3 /* (0x */
                            + 2 * sizeof(UV) + 2 /* )\0 */;
                    } else {
                        len = typelen + 3 /* (0x */
                            + 2 * sizeof(UV) + 2 /* )\0 */;
                    }

                    Newx(buffer, len, char);
                    buffer_end = retval = buffer + len;

                    /* Working backwards  */
                    *--retval = '\0';
                    *--retval = ')';
                    do {
                        *--retval = PL_hexdigit[addr & 15];
                    } while (addr >>= 4);
                    *--retval = 'x';
                    *--retval = '0';
                    *--retval = '(';

                    retval -= typelen;
                    memcpy(retval, typestr, typelen);

                    if (stashname) {
                        *--retval = '=';
                        retval -= stashnamelen;
                        memcpy(retval, stashname, stashnamelen);
                    }
                    /* retval may not neccesarily have reached the start of the
                       buffer here.  */
                    assert (retval >= buffer);

                    len = buffer_end - retval - 1; /* -1 for that \0  */
                }
                if (lp)
                    *lp = len;
                SAVEFREEPV(buffer);
                return retval;
            }
        }
        if (SvREADONLY(sv) && !SvOK(sv)) {
            if (ckWARN(WARN_UNINITIALIZED))
                report_uninit(sv);
            if (lp)
                *lp = 0;
            return (char *)"";
        }
    }
    if (SvIOK(sv) || ((SvIOKp(sv) && !SvNOKp(sv)))) {
        /* I'm assuming that if both IV and NV are equally valid then
           converting the IV is going to be more efficient */
        const U32 isUIOK = SvIsUV(sv);
        char buf[TYPE_CHARS(UV)];
        char *ebuf, *ptr;

        if (SvTYPE(sv) < SVt_PVIV)
            sv_upgrade(sv, SVt_PVIV);
        ptr = uiv_2buf(buf, SvIVX(sv), SvUVX(sv), isUIOK, &ebuf);
        /* inlined from sv_setpvn */
        SvGROW_mutable(sv, (STRLEN)(ebuf - ptr + 1));
        Move(ptr,SvPVX_mutable(sv),ebuf - ptr,char);
        SvCUR_set(sv, ebuf - ptr);
        s = SvEND(sv);
        *s = '\0';
    }
    else if (SvNOKp(sv)) {
        const int olderrno = errno;
        if (SvTYPE(sv) < SVt_PVNV)
            sv_upgrade(sv, SVt_PVNV);
        /* The +20 is pure guesswork.  Configure test needed. --jhi */
        s = SvGROW_mutable(sv, NV_DIG + 20);
        /* some Xenix systems wipe out errno here */
#ifdef apollo
        if (SvNVX(sv) == 0.0)
            my_strlcpy(s, "0", SvLEN(sv));
        else
#endif /*apollo*/
        {
            Gconvert(SvNVX(sv), NV_DIG, 0, s);
        }
        errno = olderrno;
#ifdef FIXNEGATIVEZERO
        if (*s == '-' && s[1] == '0' && !s[2])
            my_strlcpy(s, "0", SvLEN(s));
#endif
        while (*s) s++;
#ifdef hcx
        if (s[-1] == '.')
            *--s = '\0';
#endif
    }
    else {
        if (isGV_with_GP(sv))
            return glob_2pv((GV *)sv, lp);

        if (!PL_localizing && !(SvFLAGS(sv) & SVs_PADTMP) && ckWARN(WARN_UNINITIALIZED))
            report_uninit(sv);
        if (lp)
            *lp = 0;
        if (SvTYPE(sv) < SVt_PV)
            /* Typically the caller expects that sv_any is not NULL now.  */
            sv_upgrade(sv, SVt_PV);
        return (char *)"";
    }
    {
        const STRLEN len = s - SvPVX_const(sv);
        if (lp) 
            *lp = len;
        SvCUR_set(sv, len);
    }
    SvPOK_on(sv);
    DEBUG_c(PerlIO_printf(Perl_debug_log, "0x%"UVxf" 2pv(%s)\n",
                          PTR2UV(sv),SvPVX_const(sv)));
    if (flags & SV_CONST_RETURN)
        return (char *)SvPVX_const(sv);
    if (flags & SV_MUTABLE_RETURN)
        return SvPVX_mutable(sv);
    return SvPVX(sv);
}

/*
=for apidoc sv_copypv

Copies a stringified representation of the source SV into the
destination SV.  Automatically performs any necessary mg_get and
coercion of numeric values into strings.  Guaranteed to preserve
UTF-8 flag even from overloaded objects.  Similar in nature to
sv_2pv[_flags] but operates directly on an SV instead of just the
string.  Mostly uses sv_2pv_flags to do its work, except when that
would lose the UTF-8'ness of the PV.

=cut
*/

void
Perl_sv_copypv(pTHX_ SV *dsv, register SV *ssv)
{
    STRLEN len;
    const char * const s = SvPV_const(ssv,len);
    sv_setpvn(dsv,s,len);
    if (SvUTF8(ssv))
        SvUTF8_on(dsv);
    else
        SvUTF8_off(dsv);
}

/*
=for apidoc sv_2pvbyte

Return a pointer to the byte-encoded representation of the SV, and set *lp
to its length.  May cause the SV to be downgraded from UTF-8 as a
side-effect.

Usually accessed via the C<SvPVbyte> macro.

=cut
*/

char *
Perl_sv_2pvbyte(pTHX_ register SV *sv, STRLEN *lp)
{
    sv_utf8_downgrade(sv,0);
    return lp ? SvPV(sv,*lp) : SvPV_nolen(sv);
}

/*
=for apidoc sv_2pvutf8

Return a pointer to the UTF-8-encoded representation of the SV, and set *lp
to its length.  May cause the SV to be upgraded to UTF-8 as a side-effect.

Usually accessed via the C<SvPVutf8> macro.

=cut
*/

char *
Perl_sv_2pvutf8(pTHX_ register SV *sv, STRLEN *lp)
{
    sv_utf8_upgrade(sv);
    return lp ? SvPV(sv,*lp) : SvPV_nolen(sv);
}


/*
=for apidoc sv_2bool

This function is only called on magical items, and is only used by
sv_true() or its macro equivalent.

=cut
*/

bool
Perl_sv_2bool(pTHX_ register SV *sv)
{
    dVAR;
    SvGETMAGIC(sv);

    if (!SvOK(sv))
        return 0;
    if (SvROK(sv)) {
        if (SvAMAGIC(sv)) {
            SV * const tmpsv = AMG_CALLun(sv,bool_);
            if (tmpsv && (!SvROK(tmpsv) || (SvRV(tmpsv) != SvRV(sv))))
                return (bool)SvTRUE(tmpsv);
        }
        return SvRV(sv) != 0;
    }
    if (SvPOKp(sv)) {
        register XPV* const Xpvtmp = (XPV*)SvANY(sv);
        if (Xpvtmp &&
                (*sv->sv_u.svu_pv > '0' ||
                Xpvtmp->xpv_cur > 1 ||
                (Xpvtmp->xpv_cur && *sv->sv_u.svu_pv != '0')))
            return 1;
        else
            return 0;
    }
    else {
        if (SvIOKp(sv))
            return SvIVX(sv) != 0;
        else {
            if (SvNOKp(sv))
                return SvNVX(sv) != 0.0;
            else {
                if (isGV_with_GP(sv))
                    return TRUE;
                else
                    return FALSE;
            }
        }
    }
}

/*
=for apidoc sv_utf8_upgrade

Converts the PV of an SV to its UTF-8-encoded form.
Forces the SV to string form if it is not already.
Always sets the SvUTF8 flag to avoid future validity checks even
if all the bytes have hibit clear.

This is not as a general purpose byte encoding to Unicode interface:
use the Encode extension for that.

=for apidoc sv_utf8_upgrade_flags

Converts the PV of an SV to its UTF-8-encoded form.
Forces the SV to string form if it is not already.
Always sets the SvUTF8 flag to avoid future validity checks even
if all the bytes have hibit clear. If C<flags> has C<SV_GMAGIC> bit set,
will C<mg_get> on C<sv> if appropriate, else not. C<sv_utf8_upgrade> and
C<sv_utf8_upgrade_nomg> are implemented in terms of this function.

This is not as a general purpose byte encoding to Unicode interface:
use the Encode extension for that.

=cut
*/

STRLEN
Perl_sv_utf8_upgrade_flags(pTHX_ register SV *sv, I32 flags)
{
    dVAR;
    if (sv == &PL_sv_undef)
        return 0;
    if (!SvPOK(sv)) {
        STRLEN len = 0;
        if (SvREADONLY(sv) && (SvPOKp(sv) || SvIOKp(sv) || SvNOKp(sv))) {
            (void) sv_2pv_flags(sv,&len, flags);
            if (SvUTF8(sv))
                return len;
        } else {
            (void) SvPV_force(sv,len);
        }
    }

    if (SvUTF8(sv)) {
        return SvCUR(sv);
    }

    if (SvIsCOW(sv)) {
        sv_force_normal_flags(sv, 0);
    }

    if (PL_encoding && !(flags & SV_UTF8_NO_ENCODING))
        sv_recode_to_utf8(sv, PL_encoding);
    else { /* Assume Latin-1/EBCDIC */
        /* This function could be much more efficient if we
         * had a FLAG in SVs to signal if there are any hibit
         * chars in the PV.  Given that there isn't such a flag
         * make the loop as fast as possible. */
        const U8 * const s = (U8 *) SvPVX_const(sv);
        const U8 * const e = (U8 *) SvEND(sv);
        const U8 *t = s;
        
        while (t < e) {
            const U8 ch = *t++;
            /* Check for hi bit */
            if (!NATIVE_IS_INVARIANT(ch)) {
                STRLEN len = SvCUR(sv) + 1; /* Plus the \0 */
                U8 * const recoded = bytes_to_utf8((U8*)s, &len);

                SvPV_free(sv); /* No longer using what was there before. */
                SvPV_set(sv, (char*)recoded);
                SvCUR_set(sv, len - 1);
                SvLEN_set(sv, len); /* No longer know the real size. */
                break;
            }
        }
        /* Mark as UTF-8 even if no hibit - saves scanning loop */
        SvUTF8_on(sv);
    }
    return SvCUR(sv);
}

/*
=for apidoc sv_utf8_downgrade

Attempts to convert the PV of an SV from characters to bytes.
If the PV contains a character beyond byte, this conversion will fail;
in this case, either returns false or, if C<fail_ok> is not
true, croaks.

This is not as a general purpose Unicode to byte encoding interface:
use the Encode extension for that.

=cut
*/

bool
Perl_sv_utf8_downgrade(pTHX_ register SV* sv, bool fail_ok)
{
    dVAR;
    if (SvPOKp(sv) && SvUTF8(sv)) {
        if (SvCUR(sv)) {
            U8 *s;
            STRLEN len;

            if (SvIsCOW(sv)) {
                sv_force_normal_flags(sv, 0);
            }
            s = (U8 *) SvPV(sv, len);
            if (!utf8_to_bytes(s, &len)) {
                if (fail_ok)
                    return FALSE;
                else {
                    if (PL_op)
                        Perl_croak(aTHX_ "Wide character in %s",
                                   OP_DESC(PL_op));
                    else
                        Perl_croak(aTHX_ "Wide character");
                }
            }
            SvCUR_set(sv, len);
        }
    }
    SvUTF8_off(sv);
    return TRUE;
}

/*
=for apidoc sv_utf8_encode

Converts the PV of an SV to UTF-8, but then turns the C<SvUTF8>
flag off so that it looks like octets again.

=cut
*/

void
Perl_sv_utf8_encode(pTHX_ register SV *sv)
{
    if (SvIsCOW(sv)) {
        sv_force_normal_flags(sv, 0);
    }
    if (SvREADONLY(sv)) {
        Perl_croak(aTHX_ PL_no_modify);
    }
    (void) sv_utf8_upgrade(sv);
    SvUTF8_off(sv);
}

/*
=for apidoc sv_utf8_decode

If the PV of the SV is an octet sequence in UTF-8
and contains a multiple-byte character, the C<SvUTF8> flag is turned on
so that it looks like a character. If the PV contains only single-byte
characters, the C<SvUTF8> flag stays being off.
Scans PV for validity and returns false if the PV is invalid UTF-8.

=cut
*/

bool
Perl_sv_utf8_decode(pTHX_ register SV *sv)
{
    if (SvPOKp(sv)) {
        const U8 *c;
        const U8 *e;

        /* The octets may have got themselves encoded - get them back as
         * bytes
         */
        if (!sv_utf8_downgrade(sv, TRUE))
            return FALSE;

        /* it is actually just a matter of turning the utf8 flag on, but
         * we want to make sure everything inside is valid utf8 first.
         */
        c = (const U8 *) SvPVX_const(sv);
        if (!is_utf8_string(c, SvCUR(sv)+1))
            return FALSE;
        e = (const U8 *) SvEND(sv);
        while (c < e) {
            const U8 ch = *c++;
            if (!UTF8_IS_INVARIANT(ch)) {
                SvUTF8_on(sv);
                break;
            }
        }
    }
    return TRUE;
}

/*
=for apidoc sv_setsv

Copies the contents of the source SV C<ssv> into the destination SV
C<dsv>.  The source SV may be destroyed if it is mortal, so don't use this
function if the source SV needs to be reused. Does not handle 'set' magic.
Loosely speaking, it performs a copy-by-value, obliterating any previous
content of the destination.

You probably want to use one of the assortment of wrappers, such as
C<SvSetSV>, C<SvSetSV_nosteal>, C<SvSetMagicSV> and
C<SvSetMagicSV_nosteal>.

=for apidoc sv_setsv_flags

Copies the contents of the source SV C<ssv> into the destination SV
C<dsv>.  The source SV may be destroyed if it is mortal, so don't use this
function if the source SV needs to be reused. Does not handle 'set' magic.
Loosely speaking, it performs a copy-by-value, obliterating any previous
content of the destination.
If the C<flags> parameter has the C<SV_GMAGIC> bit set, will C<mg_get> on
C<ssv> if appropriate, else not. If the C<flags> parameter has the
C<NOSTEAL> bit set then the buffers of temps will not be stolen. <sv_setsv>
and C<sv_setsv_nomg> are implemented in terms of this function.

You probably want to use one of the assortment of wrappers, such as
C<SvSetSV>, C<SvSetSV_nosteal>, C<SvSetMagicSV> and
C<SvSetMagicSV_nosteal>.

This is the primary function for copying scalars, and most other
copy-ish functions and macros use this underneath.

=cut
*/

static void
S_glob_assign_glob(pTHX_ SV *dstr, SV *sstr, const int dtype)
{
    if (dtype != SVt_PVGV) {
        const char * const name = GvNAME(sstr);
        const STRLEN len = GvNAMELEN(sstr);
        /* don't upgrade SVt_PVLV: it can hold a glob */
        if (dtype != SVt_PVLV) {
            if (dtype >= SVt_PV) {
                SvPV_free(dstr);
                SvPV_set(dstr, 0);
                SvLEN_set(dstr, 0);
                SvCUR_set(dstr, 0);
            }
            sv_upgrade(dstr, SVt_PVGV);
            (void)SvOK_off(dstr);
            /* FIXME - why are we doing this, then turning it off and on again
               below?  */
            isGV_with_GP_on(dstr);
        }
        GvSTASH(dstr) = GvSTASH(sstr);
        if (GvSTASH(dstr))
            Perl_sv_add_backref(aTHX_ (SV*)GvSTASH(dstr), dstr);
        gv_name_set((GV *)dstr, name, len, GV_ADD);
        SvFAKE_on(dstr);        /* can coerce to non-glob */
    }

#ifdef GV_UNIQUE_CHECK
    if (GvUNIQUE((GV*)dstr)) {
        Perl_croak(aTHX_ PL_no_modify);
    }
#endif

    gp_free((GV*)dstr);
    isGV_with_GP_off(dstr);
    (void)SvOK_off(dstr);
    isGV_with_GP_on(dstr);
    GvINTRO_off(dstr);          /* one-shot flag */
    GvGP(dstr) = gp_ref(GvGP(sstr));
    if (SvTAINTED(sstr))
        SvTAINT(dstr);
    if (GvIMPORTED(dstr) != GVf_IMPORTED
        && CopSTASH_ne(PL_curcop, GvSTASH(dstr)))
        {
            GvIMPORTED_on(dstr);
        }
    GvMULTI_on(dstr);
    return;
}

static void
S_glob_assign_ref(pTHX_ SV *dstr, SV *sstr) {
    SV * const sref = SvREFCNT_inc(SvRV(sstr));
    SV *dref = NULL;
    const int intro = GvINTRO(dstr);
    SV **location;
    U8 import_flag = 0;
    const U32 stype = SvTYPE(sref);


#ifdef GV_UNIQUE_CHECK
    if (GvUNIQUE((GV*)dstr)) {
        Perl_croak(aTHX_ PL_no_modify);
    }
#endif

    if (intro) {
        GvINTRO_off(dstr);      /* one-shot flag */
        GvLINE(dstr) = CopLINE(PL_curcop);
        GvEGV(dstr) = (GV*)dstr;
    }
    GvMULTI_on(dstr);
    switch (stype) {
    case SVt_PVCV:
        location = (SV **) &GvCV(dstr);
        import_flag = GVf_IMPORTED_CV;
        goto common;
    case SVt_PVHV:
        location = (SV **) &GvHV(dstr);
        import_flag = GVf_IMPORTED_HV;
        goto common;
    case SVt_PVAV:
        location = (SV **) &GvAV(dstr);
        import_flag = GVf_IMPORTED_AV;
        goto common;
    case SVt_PVIO:
        location = (SV **) &GvIOp(dstr);
        goto common;
    case SVt_PVFM:
        location = (SV **) &GvFORM(dstr);
    default:
        location = &GvSV(dstr);
        import_flag = GVf_IMPORTED_SV;
    common:
        if (intro) {
            if (stype == SVt_PVCV) {
                if (GvCVGEN(dstr) && GvCV(dstr) != (CV*)sref) {
                    SvREFCNT_dec(GvCV(dstr));
                    GvCV(dstr) = NULL;
                    GvCVGEN(dstr) = 0; /* Switch off cacheness. */
                    PL_sub_generation++;
                }
            }
            SAVEGENERICSV(*location);
        }
        else
            dref = *location;
        if (stype == SVt_PVCV && *location != sref) {
            CV* const cv = (CV*)*location;
            if (cv) {
                if (!GvCVGEN((GV*)dstr) &&
                    (CvROOT(cv) || CvXSUB(cv)))
                    {
                        /* Redefining a sub - warning is mandatory if
                           it was a const and its value changed. */
                        if (CvCONST(cv) && CvCONST((CV*)sref)
                            && cv_const_sv(cv) == cv_const_sv((CV*)sref)) {
                            NOOP;
                            /* They are 2 constant subroutines generated from
                               the same constant. This probably means that
                               they are really the "same" proxy subroutine
                               instantiated in 2 places. Most likely this is
                               when a constant is exported twice.  Don't warn.
                            */
                        }
                        else if (ckWARN(WARN_REDEFINE)
                                 || (CvCONST(cv)
                                     && (!CvCONST((CV*)sref)
                                         || sv_cmp(cv_const_sv(cv),
                                                   cv_const_sv((CV*)sref))))) {
                            Perl_warner(aTHX_ packWARN(WARN_REDEFINE),
                                        (const char *)
                                        (CvCONST(cv)
                                         ? "Constant subroutine %s::%s redefined"
                                         : "Subroutine %s::%s redefined"),
                                        HvNAME_get(GvSTASH((GV*)dstr)),
                                        GvENAME((GV*)dstr));
                        }
                    }
                if (!intro)
                    cv_ckproto_len(cv, (GV*)dstr,
                                   SvPOK(sref) ? SvPVX_const(sref) : NULL,
                                   SvPOK(sref) ? SvCUR(sref) : 0);
            }
            GvCVGEN(dstr) = 0; /* Switch off cacheness. */
            GvASSUMECV_on(dstr);
            PL_sub_generation++;
        }
        *location = sref;
        if (import_flag && !(GvFLAGS(dstr) & import_flag)
            && CopSTASH_ne(PL_curcop, GvSTASH(dstr))) {
            GvFLAGS(dstr) |= import_flag;
        }
        break;
    }
    SvREFCNT_dec(dref);
    if (SvTAINTED(sstr))
        SvTAINT(dstr);
    return;
}

void
Perl_sv_setsv_flags(pTHX_ SV *dstr, register SV *sstr, I32 flags)
{
    dVAR;
    register U32 sflags;
    register int dtype;
    register svtype stype;

    if (sstr == dstr)
        return;

    if (SvIS_FREED(dstr)) {
        Perl_croak(aTHX_ "panic: attempt to copy value %" SVf
                   " to a freed scalar %p", sstr, dstr);
    }
    SV_CHECK_THINKFIRST_COW_DROP(dstr);
    if (!sstr)
        sstr = &PL_sv_undef;
    if (SvIS_FREED(sstr)) {
        Perl_croak(aTHX_ "panic: attempt to copy freed scalar %p to %p", sstr,
                   dstr);
    }
    stype = SvTYPE(sstr);
    dtype = SvTYPE(dstr);

    SvAMAGIC_off(dstr);
    if ( SvVOK(dstr) )
    {
        /* need to nuke the magic */
        mg_free(dstr);
        SvRMAGICAL_off(dstr);
    }

    /* There's a lot of redundancy below but we're going for speed here */

    switch (stype) {
    case SVt_NULL:
      undef_sstr:
        if (dtype != SVt_PVGV) {
            (void)SvOK_off(dstr);
            return;
        }
        break;
    case SVt_IV:
        if (SvIOK(sstr)) {
            switch (dtype) {
            case SVt_NULL:
                sv_upgrade(dstr, SVt_IV);
                break;
            case SVt_NV:
            case SVt_RV:
            case SVt_PV:
                sv_upgrade(dstr, SVt_PVIV);
                break;
            case SVt_PVGV:
                goto end_of_first_switch;
            }
            (void)SvIOK_only(dstr);
            SvIV_set(dstr,  SvIVX(sstr));
            if (SvIsUV(sstr))
                SvIsUV_on(dstr);
            /* SvTAINTED can only be true if the SV has taint magic, which in
               turn means that the SV type is PVMG (or greater). This is the
               case statement for SVt_IV, so this cannot be true (whatever gcov
               may say).  */
            assert(!SvTAINTED(sstr));
            return;
        }
        goto undef_sstr;

    case SVt_NV:
        if (SvNOK(sstr)) {
            switch (dtype) {
            case SVt_NULL:
            case SVt_IV:
                sv_upgrade(dstr, SVt_NV);
                break;
            case SVt_RV:
            case SVt_PV:
            case SVt_PVIV:
                sv_upgrade(dstr, SVt_PVNV);
                break;
            case SVt_PVGV:
                goto end_of_first_switch;
            }
            SvNV_set(dstr, SvNVX(sstr));
            (void)SvNOK_only(dstr);
            /* SvTAINTED can only be true if the SV has taint magic, which in
               turn means that the SV type is PVMG (or greater). This is the
               case statement for SVt_NV, so this cannot be true (whatever gcov
               may say).  */
            assert(!SvTAINTED(sstr));
            return;
        }
        goto undef_sstr;

    case SVt_RV:
        if (dtype < SVt_RV)
            sv_upgrade(dstr, SVt_RV);
        break;
    case SVt_PVFM:
#ifdef PERL_OLD_COPY_ON_WRITE
        if ((SvFLAGS(sstr) & CAN_COW_MASK) == CAN_COW_FLAGS) {
            if (dtype < SVt_PVIV)
                sv_upgrade(dstr, SVt_PVIV);
            break;
        }
        /* Fall through */
#endif
    case SVt_PV:
        if (dtype < SVt_PV)
            sv_upgrade(dstr, SVt_PV);
        break;
    case SVt_PVIV:
        if (dtype < SVt_PVIV)
            sv_upgrade(dstr, SVt_PVIV);
        break;
    case SVt_PVNV:
        if (dtype < SVt_PVNV)
            sv_upgrade(dstr, SVt_PVNV);
        break;
    default:
        {
        const char * const type = sv_reftype(sstr,0);
        if (PL_op)
            Perl_croak(aTHX_ "Bizarre copy of %s in %s", type, OP_NAME(PL_op));
        else
            Perl_croak(aTHX_ "Bizarre copy of %s", type);
        }
        break;

        /* case SVt_BIND: */
    case SVt_PVGV:
        if (isGV_with_GP(sstr) && dtype <= SVt_PVGV) {
            glob_assign_glob(dstr, sstr, dtype);
            return;
        }
        /* SvVALID means that this PVGV is playing at being an FBM.  */
        /*FALLTHROUGH*/

    case SVt_PVMG:
    case SVt_PVLV:
        if (SvGMAGICAL(sstr) && (flags & SV_GMAGIC)) {
            mg_get(sstr);
            if (SvTYPE(sstr) != stype) {
                stype = SvTYPE(sstr);
                if (isGV_with_GP(sstr) && stype == SVt_PVGV && dtype <= SVt_PVGV) {
                    glob_assign_glob(dstr, sstr, dtype);
                    return;
                }
            }
        }
        if (stype == SVt_PVLV)
            SvUPGRADE(dstr, SVt_PVNV);
        else
            SvUPGRADE(dstr, (svtype)stype);
    }
 end_of_first_switch:

    /* dstr may have been upgraded.  */
    dtype = SvTYPE(dstr);
    sflags = SvFLAGS(sstr);

    if (dtype == SVt_PVCV) {
        /* Assigning to a subroutine sets the prototype.  */
        if (SvOK(sstr)) {
            STRLEN len;
            const char *const ptr = SvPV_const(sstr, len);

            SvGROW(dstr, len + 1);
            Copy(ptr, SvPVX(dstr), len + 1, char);
            SvCUR_set(dstr, len);
            SvPOK_only(dstr);
        } else {
            SvOK_off(dstr);
        }
    } else if (sflags & SVf_ROK) {
        if (isGV_with_GP(dstr) && dtype == SVt_PVGV
            && SvTYPE(SvRV(sstr)) == SVt_PVGV) {
            sstr = SvRV(sstr);
            if (sstr == dstr) {
                if (GvIMPORTED(dstr) != GVf_IMPORTED
                    && CopSTASH_ne(PL_curcop, GvSTASH(dstr)))
                {
                    GvIMPORTED_on(dstr);
                }
                GvMULTI_on(dstr);
                return;
            }
            glob_assign_glob(dstr, sstr, dtype);
            return;
        }

        if (dtype >= SVt_PV) {
            if (dtype == SVt_PVGV) {
                glob_assign_ref(dstr, sstr);
                return;
            }
            if (SvPVX_const(dstr)) {
                SvPV_free(dstr);
                SvLEN_set(dstr, 0);
                SvCUR_set(dstr, 0);
            }
        }
        (void)SvOK_off(dstr);
        SvRV_set(dstr, SvREFCNT_inc(SvRV(sstr)));
        SvFLAGS(dstr) |= sflags & SVf_ROK;
        assert(!(sflags & SVp_NOK));
        assert(!(sflags & SVp_IOK));
        assert(!(sflags & SVf_NOK));
        assert(!(sflags & SVf_IOK));
    }
    else if (dtype == SVt_PVGV && isGV_with_GP(dstr)) {
        if (!(sflags & SVf_OK)) {
            if (ckWARN(WARN_MISC))
                Perl_warner(aTHX_ packWARN(WARN_MISC),
                            "Undefined value assigned to typeglob");
        }
        else {
            GV *gv = gv_fetchsv(sstr, GV_ADD, SVt_PVGV);
            if (dstr != (SV*)gv) {
                if (GvGP(dstr))
                    gp_free((GV*)dstr);
                GvGP(dstr) = gp_ref(GvGP(gv));
            }
        }
    }
    else if (sflags & SVp_POK) {
        bool isSwipe = 0;

        /*
         * Check to see if we can just swipe the string.  If so, it's a
         * possible small lose on short strings, but a big win on long ones.
         * It might even be a win on short strings if SvPVX_const(dstr)
         * has to be allocated and SvPVX_const(sstr) has to be freed.
         * Likewise if we can set up COW rather than doing an actual copy, we
         * drop to the else clause, as the swipe code and the COW setup code
         * have much in common.
         */

        /* Whichever path we take through the next code, we want this true,
           and doing it now facilitates the COW check.  */
        (void)SvPOK_only(dstr);

        if (
            /* If we're already COW then this clause is not true, and if COW
               is allowed then we drop down to the else and make dest COW 
               with us.  If caller hasn't said that we're allowed to COW
               shared hash keys then we don't do the COW setup, even if the
               source scalar is a shared hash key scalar.  */
            (((flags & SV_COW_SHARED_HASH_KEYS)
               ? (sflags & (SVf_FAKE|SVf_READONLY)) != (SVf_FAKE|SVf_READONLY)
               : 1 /* If making a COW copy is forbidden then the behaviour we
                       desire is as if the source SV isn't actually already
                       COW, even if it is.  So we act as if the source flags
                       are not COW, rather than actually testing them.  */
              )
#ifndef PERL_OLD_COPY_ON_WRITE
             /* The change that added SV_COW_SHARED_HASH_KEYS makes the logic
                when PERL_OLD_COPY_ON_WRITE is defined a little wrong.
                Conceptually PERL_OLD_COPY_ON_WRITE being defined should
                override SV_COW_SHARED_HASH_KEYS, because it means "always COW"
                but in turn, it's somewhat dead code, never expected to go
                live, but more kept as a placeholder on how to do it better
                in a newer implementation.  */
             /* If we are COW and dstr is a suitable target then we drop down
                into the else and make dest a COW of us.  */
             || (SvFLAGS(dstr) & CAN_COW_MASK) != CAN_COW_FLAGS
#endif
             )
            &&
            !(isSwipe =
                 (sflags & SVs_TEMP) &&   /* slated for free anyway? */
                 !(sflags & SVf_OOK) &&   /* and not involved in OOK hack? */
                 (!(flags & SV_NOSTEAL)) &&
                                        /* and we're allowed to steal temps */
                 SvREFCNT(sstr) == 1 &&   /* and no other references to it? */
                 SvLEN(sstr)    &&        /* and really is a string */
                                /* and won't be needed again, potentially */
              !(PL_op && PL_op->op_type == OP_AASSIGN))
#ifdef PERL_OLD_COPY_ON_WRITE
            && !((sflags & CAN_COW_MASK) == CAN_COW_FLAGS
                 && (SvFLAGS(dstr) & CAN_COW_MASK) == CAN_COW_FLAGS
                 && SvTYPE(sstr) >= SVt_PVIV)
#endif
            ) {
            /* Failed the swipe test, and it's not a shared hash key either.
               Have to copy the string.  */
            STRLEN len = SvCUR(sstr);
            SvGROW(dstr, len + 1);      /* inlined from sv_setpvn */
            Move(SvPVX_const(sstr),SvPVX(dstr),len,char);
            SvCUR_set(dstr, len);
            *SvEND(dstr) = '\0';
        } else {
            /* If PERL_OLD_COPY_ON_WRITE is not defined, then isSwipe will always
               be true in here.  */
            /* Either it's a shared hash key, or it's suitable for
               copy-on-write or we can swipe the string.  */
            if (DEBUG_C_TEST) {
                PerlIO_printf(Perl_debug_log, "Copy on write: sstr --> dstr\n");
                sv_dump(sstr);
                sv_dump(dstr);
            }
#ifdef PERL_OLD_COPY_ON_WRITE
            if (!isSwipe) {
                /* I believe I should acquire a global SV mutex if
                   it's a COW sv (not a shared hash key) to stop
                   it going un copy-on-write.
                   If the source SV has gone un copy on write between up there
                   and down here, then (assert() that) it is of the correct
                   form to make it copy on write again */
                if ((sflags & (SVf_FAKE | SVf_READONLY))
                    != (SVf_FAKE | SVf_READONLY)) {
                    SvREADONLY_on(sstr);
                    SvFAKE_on(sstr);
                    /* Make the source SV into a loop of 1.
                       (about to become 2) */
                    SV_COW_NEXT_SV_SET(sstr, sstr);
                }
            }
#endif
            /* Initial code is common.  */
            if (SvPVX_const(dstr)) {    /* we know that dtype >= SVt_PV */
                SvPV_free(dstr);
            }

            if (!isSwipe) {
                /* making another shared SV.  */
                STRLEN cur = SvCUR(sstr);
                STRLEN len = SvLEN(sstr);
#ifdef PERL_OLD_COPY_ON_WRITE
                if (len) {
                    assert (SvTYPE(dstr) >= SVt_PVIV);
                    /* SvIsCOW_normal */
                    /* splice us in between source and next-after-source.  */
                    SV_COW_NEXT_SV_SET(dstr, SV_COW_NEXT_SV(sstr));
                    SV_COW_NEXT_SV_SET(sstr, dstr);
                    SvPV_set(dstr, SvPVX_mutable(sstr));
                } else
#endif
                {
                    /* SvIsCOW_shared_hash */
                    DEBUG_C(PerlIO_printf(Perl_debug_log,
                                          "Copy on write: Sharing hash\n"));

                    assert (SvTYPE(dstr) >= SVt_PV);
                    SvPV_set(dstr,
                             HEK_KEY(share_hek_hek(SvSHARED_HEK_FROM_PV(SvPVX_const(sstr)))));
                }
                SvLEN_set(dstr, len);
                SvCUR_set(dstr, cur);
                SvREADONLY_on(dstr);
                SvFAKE_on(dstr);
                /* Relesase a global SV mutex.  */
            }
            else
                {       /* Passes the swipe test.  */
                SvPV_set(dstr, SvPVX_mutable(sstr));
                SvLEN_set(dstr, SvLEN(sstr));
                SvCUR_set(dstr, SvCUR(sstr));

                SvTEMP_off(dstr);
                (void)SvOK_off(sstr);   /* NOTE: nukes most SvFLAGS on sstr */
                SvPV_set(sstr, NULL);
                SvLEN_set(sstr, 0);
                SvCUR_set(sstr, 0);
                SvTEMP_off(sstr);
            }
        }
        if (sflags & SVp_NOK) {
            SvNV_set(dstr, SvNVX(sstr));
        }
        if (sflags & SVp_IOK) {
            SvRELEASE_IVX(dstr);
            SvIV_set(dstr, SvIVX(sstr));
            /* Must do this otherwise some other overloaded use of 0x80000000
               gets confused. I guess SVpbm_VALID */
            if (sflags & SVf_IVisUV)
                SvIsUV_on(dstr);
        }
        SvFLAGS(dstr) |= sflags & (SVf_IOK|SVp_IOK|SVf_NOK|SVp_NOK|SVf_UTF8);
        {
            const MAGIC * const smg = SvVSTRING_mg(sstr);
            if (smg) {
                sv_magic(dstr, NULL, PERL_MAGIC_vstring,
                         smg->mg_ptr, smg->mg_len);
                SvRMAGICAL_on(dstr);
            }
        }
    }
    else if (sflags & (SVp_IOK|SVp_NOK)) {
        (void)SvOK_off(dstr);
        SvFLAGS(dstr) |= sflags & (SVf_IOK|SVp_IOK|SVf_IVisUV|SVf_NOK|SVp_NOK);
        if (sflags & SVp_IOK) {
            /* XXXX Do we want to set IsUV for IV(ROK)?  Be extra safe... */
            SvIV_set(dstr, SvIVX(sstr));
        }
        if (sflags & SVp_NOK) {
            SvNV_set(dstr, SvNVX(sstr));
        }
    }
    else {
        if (isGV_with_GP(sstr)) {
            /* This stringification rule for globs is spread in 3 places.
               This feels bad. FIXME.  */
            const U32 wasfake = sflags & SVf_FAKE;

            /* FAKE globs can get coerced, so need to turn this off
               temporarily if it is on.  */
            SvFAKE_off(sstr);
            gv_efullname3(dstr, (GV *)sstr, "*");
            SvFLAGS(sstr) |= wasfake;
        }
        else
            (void)SvOK_off(dstr);
    }
    if (SvTAINTED(sstr))
        SvTAINT(dstr);
}

/*
=for apidoc sv_setsv_mg

Like C<sv_setsv>, but also handles 'set' magic.

=cut
*/

void
Perl_sv_setsv_mg(pTHX_ SV *dstr, register SV *sstr)
{
    sv_setsv(dstr,sstr);
    SvSETMAGIC(dstr);
}

#ifdef PERL_OLD_COPY_ON_WRITE
SV *
Perl_sv_setsv_cow(pTHX_ SV *dstr, SV *sstr)
{
    STRLEN cur = SvCUR(sstr);
    STRLEN len = SvLEN(sstr);
    register char *new_pv;

    if (DEBUG_C_TEST) {
        PerlIO_printf(Perl_debug_log, "Fast copy on write: %p -> %p\n",
                      sstr, dstr);
        sv_dump(sstr);
        if (dstr)
                    sv_dump(dstr);
    }

    if (dstr) {
        if (SvTHINKFIRST(dstr))
            sv_force_normal_flags(dstr, SV_COW_DROP_PV);
        else if (SvPVX_const(dstr))
            Safefree(SvPVX_const(dstr));
    }
    else
        new_SV(dstr);
    SvUPGRADE(dstr, SVt_PVIV);

    assert (SvPOK(sstr));
    assert (SvPOKp(sstr));
    assert (!SvIOK(sstr));
    assert (!SvIOKp(sstr));
    assert (!SvNOK(sstr));
    assert (!SvNOKp(sstr));

    if (SvIsCOW(sstr)) {

        if (SvLEN(sstr) == 0) {
            /* source is a COW shared hash key.  */
            DEBUG_C(PerlIO_printf(Perl_debug_log,
                                  "Fast copy on write: Sharing hash\n"));
            new_pv = HEK_KEY(share_hek_hek(SvSHARED_HEK_FROM_PV(SvPVX_const(sstr))));
            goto common_exit;
        }
        SV_COW_NEXT_SV_SET(dstr, SV_COW_NEXT_SV(sstr));
    } else {
        assert ((SvFLAGS(sstr) & CAN_COW_MASK) == CAN_COW_FLAGS);
        SvUPGRADE(sstr, SVt_PVIV);
        SvREADONLY_on(sstr);
        SvFAKE_on(sstr);
        DEBUG_C(PerlIO_printf(Perl_debug_log,
                              "Fast copy on write: Converting sstr to COW\n"));
        SV_COW_NEXT_SV_SET(dstr, sstr);
    }
    SV_COW_NEXT_SV_SET(sstr, dstr);
    new_pv = SvPVX_mutable(sstr);

  common_exit:
    SvPV_set(dstr, new_pv);
    SvFLAGS(dstr) = (SVt_PVIV|SVf_POK|SVp_POK|SVf_FAKE|SVf_READONLY);
    if (SvUTF8(sstr))
        SvUTF8_on(dstr);
    SvLEN_set(dstr, len);
    SvCUR_set(dstr, cur);
    if (DEBUG_C_TEST) {
        sv_dump(dstr);
    }
    return dstr;
}
#endif

/*
=for apidoc sv_setpvn

Copies a string into an SV.  The C<len> parameter indicates the number of
bytes to be copied.  If the C<ptr> argument is NULL the SV will become
undefined.  Does not handle 'set' magic.  See C<sv_setpvn_mg>.

=cut
*/

void
Perl_sv_setpvn(pTHX_ register SV *sv, register const char *ptr, register STRLEN len)
{
    dVAR;
    register char *dptr;

    SV_CHECK_THINKFIRST_COW_DROP(sv);
    if (!ptr) {
        (void)SvOK_off(sv);
        return;
    }
    else {
        /* len is STRLEN which is unsigned, need to copy to signed */
        const IV iv = len;
        if (iv < 0)
            Perl_croak(aTHX_ "panic: sv_setpvn called with negative strlen");
    }
    SvUPGRADE(sv, SVt_PV);

    dptr = SvGROW(sv, len + 1);
    Move(ptr,dptr,len,char);
    dptr[len] = '\0';
    SvCUR_set(sv, len);
    (void)SvPOK_only_UTF8(sv);          /* validate pointer */
    SvTAINT(sv);
}

/*
=for apidoc sv_setpvn_mg

Like C<sv_setpvn>, but also handles 'set' magic.

=cut
*/

void
Perl_sv_setpvn_mg(pTHX_ register SV *sv, register const char *ptr, register STRLEN len)
{
    sv_setpvn(sv,ptr,len);
    SvSETMAGIC(sv);
}

/*
=for apidoc sv_setpv

Copies a string into an SV.  The string must be null-terminated.  Does not
handle 'set' magic.  See C<sv_setpv_mg>.

=cut
*/

void
Perl_sv_setpv(pTHX_ register SV *sv, register const char *ptr)
{
    dVAR;
    register STRLEN len;

    SV_CHECK_THINKFIRST_COW_DROP(sv);
    if (!ptr) {
        (void)SvOK_off(sv);
        return;
    }
    len = strlen(ptr);
    SvUPGRADE(sv, SVt_PV);

    SvGROW(sv, len + 1);
    Move(ptr,SvPVX(sv),len+1,char);
    SvCUR_set(sv, len);
    (void)SvPOK_only_UTF8(sv);          /* validate pointer */
    SvTAINT(sv);
}

/*
=for apidoc sv_setpv_mg

Like C<sv_setpv>, but also handles 'set' magic.

=cut
*/

void
Perl_sv_setpv_mg(pTHX_ register SV *sv, register const char *ptr)
{
    sv_setpv(sv,ptr);
    SvSETMAGIC(sv);
}

/*
=for apidoc sv_usepvn_flags

Tells an SV to use C<ptr> to find its string value.  Normally the
string is stored inside the SV but sv_usepvn allows the SV to use an
outside string.  The C<ptr> should point to memory that was allocated
by C<malloc>.  The string length, C<len>, must be supplied.  By default
this function will realloc (i.e. move) the memory pointed to by C<ptr>,
so that pointer should not be freed or used by the programmer after
giving it to sv_usepvn, and neither should any pointers from "behind"
that pointer (e.g. ptr + 1) be used.

If C<flags> & SV_SMAGIC is true, will call SvSETMAGIC. If C<flags> &
SV_HAS_TRAILING_NUL is true, then C<ptr[len]> must be NUL, and the realloc
will be skipped. (i.e. the buffer is actually at least 1 byte longer than
C<len>, and already meets the requirements for storing in C<SvPVX>)

=cut
*/

void
Perl_sv_usepvn_flags(pTHX_ SV *sv, char *ptr, STRLEN len, U32 flags)
{
    dVAR;
    STRLEN allocate;
    SV_CHECK_THINKFIRST_COW_DROP(sv);
    SvUPGRADE(sv, SVt_PV);
    if (!ptr) {
        (void)SvOK_off(sv);
        if (flags & SV_SMAGIC)
            SvSETMAGIC(sv);
        return;
    }
    if (SvPVX_const(sv))
        SvPV_free(sv);

#ifdef DEBUGGING
    if (flags & SV_HAS_TRAILING_NUL)
        assert(ptr[len] == '\0');
#endif

    allocate = (flags & SV_HAS_TRAILING_NUL)
        ? len + 1: PERL_STRLEN_ROUNDUP(len + 1);
    if (flags & SV_HAS_TRAILING_NUL) {
        /* It's long enough - do nothing.
           Specfically Perl_newCONSTSUB is relying on this.  */
    } else {
#ifdef DEBUGGING
        /* Force a move to shake out bugs in callers.  */
        char *new_ptr = (char*)safemalloc(allocate);
        Copy(ptr, new_ptr, len, char);
        PoisonFree(ptr,len,char);
        Safefree(ptr);
        ptr = new_ptr;
#else
        ptr = (char*) saferealloc (ptr, allocate);
#endif
    }
    SvPV_set(sv, ptr);
    SvCUR_set(sv, len);
    SvLEN_set(sv, allocate);
    if (!(flags & SV_HAS_TRAILING_NUL)) {
        *SvEND(sv) = '\0';
    }
    (void)SvPOK_only_UTF8(sv);          /* validate pointer */
    SvTAINT(sv);
    if (flags & SV_SMAGIC)
        SvSETMAGIC(sv);
}

#ifdef PERL_OLD_COPY_ON_WRITE
/* Need to do this *after* making the SV normal, as we need the buffer
   pointer to remain valid until after we've copied it.  If we let go too early,
   another thread could invalidate it by unsharing last of the same hash key
   (which it can do by means other than releasing copy-on-write Svs)
   or by changing the other copy-on-write SVs in the loop.  */
STATIC void
S_sv_release_COW(pTHX_ register SV *sv, const char *pvx, STRLEN len, SV *after)
{
    if (len) { /* this SV was SvIsCOW_normal(sv) */
         /* we need to find the SV pointing to us.  */
        SV *current = SV_COW_NEXT_SV(after);

        if (current == sv) {
            /* The SV we point to points back to us (there were only two of us
               in the loop.)
               Hence other SV is no longer copy on write either.  */
            SvFAKE_off(after);
            SvREADONLY_off(after);
        } else {
            /* We need to follow the pointers around the loop.  */
            SV *next;
            while ((next = SV_COW_NEXT_SV(current)) != sv) {
                assert (next);
                current = next;
                 /* don't loop forever if the structure is bust, and we have
                    a pointer into a closed loop.  */
                assert (current != after);
                assert (SvPVX_const(current) == pvx);
            }
            /* Make the SV before us point to the SV after us.  */
            SV_COW_NEXT_SV_SET(current, after);
        }
    } else {
        unshare_hek(SvSHARED_HEK_FROM_PV(pvx));
    }
}

int
Perl_sv_release_IVX(pTHX_ register SV *sv)
{
    if (SvIsCOW(sv))
        sv_force_normal_flags(sv, 0);
    SvOOK_off(sv);
    return 0;
}
#endif
/*
=for apidoc sv_force_normal_flags

Undo various types of fakery on an SV: if the PV is a shared string, make
a private copy; if we're a ref, stop refing; if we're a glob, downgrade to
an xpvmg; if we're a copy-on-write scalar, this is the on-write time when
we do the copy, and is also used locally. If C<SV_COW_DROP_PV> is set
then a copy-on-write scalar drops its PV buffer (if any) and becomes
SvPOK_off rather than making a copy. (Used where this scalar is about to be
set to some other value.) In addition, the C<flags> parameter gets passed to
C<sv_unref_flags()> when unrefing. C<sv_force_normal> calls this function
with flags set to 0.

=cut
*/

void
Perl_sv_force_normal_flags(pTHX_ register SV *sv, U32 flags)
{
    dVAR;
#ifdef PERL_OLD_COPY_ON_WRITE
    if (SvREADONLY(sv)) {
        /* At this point I believe I should acquire a global SV mutex.  */
        if (SvFAKE(sv)) {
            const char * const pvx = SvPVX_const(sv);
            const STRLEN len = SvLEN(sv);
            const STRLEN cur = SvCUR(sv);
            SV * const next = SV_COW_NEXT_SV(sv);   /* next COW sv in the loop. */
            if (DEBUG_C_TEST) {
                PerlIO_printf(Perl_debug_log,
                              "Copy on write: Force normal %ld\n",
                              (long) flags);
                sv_dump(sv);
            }
            SvFAKE_off(sv);
            SvREADONLY_off(sv);
            /* This SV doesn't own the buffer, so need to Newx() a new one:  */
            SvPV_set(sv, NULL);
            SvLEN_set(sv, 0);
            if (flags & SV_COW_DROP_PV) {
                /* OK, so we don't need to copy our buffer.  */
                SvPOK_off(sv);
            } else {
                SvGROW(sv, cur + 1);
                Move(pvx,SvPVX(sv),cur,char);
                SvCUR_set(sv, cur);
                *SvEND(sv) = '\0';
            }
            sv_release_COW(sv, pvx, len, next);
            if (DEBUG_C_TEST) {
                sv_dump(sv);
            }
        }
        else if (IN_PERL_RUNTIME)
            Perl_croak(aTHX_ PL_no_modify);
        /* At this point I believe that I can drop the global SV mutex.  */
    }
#else
    if (SvREADONLY(sv)) {
        if (SvFAKE(sv)) {
            const char * const pvx = SvPVX_const(sv);
            const STRLEN len = SvCUR(sv);
            SvFAKE_off(sv);
            SvREADONLY_off(sv);
            SvPV_set(sv, NULL);
            SvLEN_set(sv, 0);
            SvGROW(sv, len + 1);
            Move(pvx,SvPVX(sv),len,char);
            *SvEND(sv) = '\0';
            unshare_hek(SvSHARED_HEK_FROM_PV(pvx));
        }
        else if (IN_PERL_RUNTIME)
            Perl_croak(aTHX_ PL_no_modify);
    }
#endif
    if (SvROK(sv))
        sv_unref_flags(sv, flags);
    else if (SvFAKE(sv) && SvTYPE(sv) == SVt_PVGV)
        sv_unglob(sv);
}

/*
=for apidoc sv_chop

Efficient removal of characters from the beginning of the string buffer.
SvPOK(sv) must be true and the C<ptr> must be a pointer to somewhere inside
the string buffer.  The C<ptr> becomes the first character of the adjusted
string. Uses the "OOK hack".
Beware: after this function returns, C<ptr> and SvPVX_const(sv) may no longer
refer to the same chunk of data.

=cut
*/

void
Perl_sv_chop(pTHX_ register SV *sv, register const char *ptr)
{
    register STRLEN delta;
    if (!ptr || !SvPOKp(sv))
        return;
    delta = ptr - SvPVX_const(sv);
    SV_CHECK_THINKFIRST(sv);
    if (SvTYPE(sv) < SVt_PVIV)
        sv_upgrade(sv,SVt_PVIV);

    if (!SvOOK(sv)) {
        if (!SvLEN(sv)) { /* make copy of shared string */
            const char *pvx = SvPVX_const(sv);
            const STRLEN len = SvCUR(sv);
            SvGROW(sv, len + 1);
            Move(pvx,SvPVX(sv),len,char);
            *SvEND(sv) = '\0';
        }
        SvIV_set(sv, 0);
        /* Same SvOOK_on but SvOOK_on does a SvIOK_off
           and we do that anyway inside the SvNIOK_off
        */
        SvFLAGS(sv) |= SVf_OOK;
    }
    SvNIOK_off(sv);
    SvLEN_set(sv, SvLEN(sv) - delta);
    SvCUR_set(sv, SvCUR(sv) - delta);
    SvPV_set(sv, SvPVX(sv) + delta);
    SvIV_set(sv, SvIVX(sv) + delta);
}

/*
=for apidoc sv_catpvn

Concatenates the string onto the end of the string which is in the SV.  The
C<len> indicates number of bytes to copy.  If the SV has the UTF-8
status set, then the bytes appended should be valid UTF-8.
Handles 'get' magic, but not 'set' magic.  See C<sv_catpvn_mg>.

=for apidoc sv_catpvn_flags

Concatenates the string onto the end of the string which is in the SV.  The
C<len> indicates number of bytes to copy.  If the SV has the UTF-8
status set, then the bytes appended should be valid UTF-8.
If C<flags> has C<SV_GMAGIC> bit set, will C<mg_get> on C<dsv> if
appropriate, else not. C<sv_catpvn> and C<sv_catpvn_nomg> are implemented
in terms of this function.

=cut
*/

void
Perl_sv_catpvn_flags(pTHX_ register SV *dsv, register const char *sstr, register STRLEN slen, I32 flags)
{
    dVAR;
    STRLEN dlen;
    const char * const dstr = SvPV_force_flags(dsv, dlen, flags);

    SvGROW(dsv, dlen + slen + 1);
    if (sstr == dstr)
        sstr = SvPVX_const(dsv);
    Move(sstr, SvPVX(dsv) + dlen, slen, char);
    SvCUR_set(dsv, SvCUR(dsv) + slen);
    *SvEND(dsv) = '\0';
    (void)SvPOK_only_UTF8(dsv);         /* validate pointer */
    SvTAINT(dsv);
    if (flags & SV_SMAGIC)
        SvSETMAGIC(dsv);
}

/*
=for apidoc sv_catsv

Concatenates the string from SV C<ssv> onto the end of the string in
SV C<dsv>.  Modifies C<dsv> but not C<ssv>.  Handles 'get' magic, but
not 'set' magic.  See C<sv_catsv_mg>.

=for apidoc sv_catsv_flags

Concatenates the string from SV C<ssv> onto the end of the string in
SV C<dsv>.  Modifies C<dsv> but not C<ssv>.  If C<flags> has C<SV_GMAGIC>
bit set, will C<mg_get> on the SVs if appropriate, else not. C<sv_catsv>
and C<sv_catsv_nomg> are implemented in terms of this function.

=cut */

void
Perl_sv_catsv_flags(pTHX_ SV *dsv, register SV *ssv, I32 flags)
{
    dVAR;
    if (ssv) {
        STRLEN slen;
        const char *spv = SvPV_const(ssv, slen);
        if (spv) {
            /*  sutf8 and dutf8 were type bool, but under USE_ITHREADS,
                gcc version 2.95.2 20000220 (Debian GNU/Linux) for
                Linux xxx 2.2.17 on sparc64 with gcc -O2, we erroneously
                get dutf8 = 0x20000000, (i.e.  SVf_UTF8) even though
                dsv->sv_flags doesn't have that bit set.
                Andy Dougherty  12 Oct 2001
            */
            const I32 sutf8 = DO_UTF8(ssv);
            I32 dutf8;

            if (SvGMAGICAL(dsv) && (flags & SV_GMAGIC))
                mg_get(dsv);
            dutf8 = DO_UTF8(dsv);

            if (dutf8 != sutf8) {
                if (dutf8) {
                    /* Not modifying source SV, so taking a temporary copy. */
                    SV* const csv = sv_2mortal(newSVpvn(spv, slen));

                    sv_utf8_upgrade(csv);
                    spv = SvPV_const(csv, slen);
                }
                else
                    sv_utf8_upgrade_nomg(dsv);
            }
            sv_catpvn_nomg(dsv, spv, slen);
        }
    }
    if (flags & SV_SMAGIC)
        SvSETMAGIC(dsv);
}

/*
=for apidoc sv_catpv

Concatenates the string onto the end of the string which is in the SV.
If the SV has the UTF-8 status set, then the bytes appended should be
valid UTF-8.  Handles 'get' magic, but not 'set' magic.  See C<sv_catpv_mg>.

=cut */

void
Perl_sv_catpv(pTHX_ register SV *sv, register const char *ptr)
{
    dVAR;
    register STRLEN len;
    STRLEN tlen;
    char *junk;

    if (!ptr)
        return;
    junk = SvPV_force(sv, tlen);
    len = strlen(ptr);
    SvGROW(sv, tlen + len + 1);
    if (ptr == junk)
        ptr = SvPVX_const(sv);
    Move(ptr,SvPVX(sv)+tlen,len+1,char);
    SvCUR_set(sv, SvCUR(sv) + len);
    (void)SvPOK_only_UTF8(sv);          /* validate pointer */
    SvTAINT(sv);
}

/*
=for apidoc sv_catpv_mg

Like C<sv_catpv>, but also handles 'set' magic.

=cut
*/

void
Perl_sv_catpv_mg(pTHX_ register SV *sv, register const char *ptr)
{
    sv_catpv(sv,ptr);
    SvSETMAGIC(sv);
}

/*
=for apidoc newSV

Creates a new SV.  A non-zero C<len> parameter indicates the number of
bytes of preallocated string space the SV should have.  An extra byte for a
trailing NUL is also reserved.  (SvPOK is not set for the SV even if string
space is allocated.)  The reference count for the new SV is set to 1.

In 5.9.3, newSV() replaces the older NEWSV() API, and drops the first
parameter, I<x>, a debug aid which allowed callers to identify themselves.
This aid has been superseded by a new build option, PERL_MEM_LOG (see
L<perlhack/PERL_MEM_LOG>).  The older API is still there for use in XS
modules supporting older perls.

=cut
*/

SV *
Perl_newSV(pTHX_ STRLEN len)
{
    dVAR;
    register SV *sv;

    new_SV(sv);
    if (len) {
        sv_upgrade(sv, SVt_PV);
        SvGROW(sv, len + 1);
    }
    return sv;
}
/*
=for apidoc sv_magicext

Adds magic to an SV, upgrading it if necessary. Applies the
supplied vtable and returns a pointer to the magic added.

Note that C<sv_magicext> will allow things that C<sv_magic> will not.
In particular, you can add magic to SvREADONLY SVs, and add more than
one instance of the same 'how'.

If C<namlen> is greater than zero then a C<savepvn> I<copy> of C<name> is
stored, if C<namlen> is zero then C<name> is stored as-is and - as another
special case - if C<(name && namlen == HEf_SVKEY)> then C<name> is assumed
to contain an C<SV*> and is stored as-is with its REFCNT incremented.

(This is now used as a subroutine by C<sv_magic>.)

=cut
*/
MAGIC * 
Perl_sv_magicext(pTHX_ SV* sv, SV* obj, int how, const MGVTBL *vtable,
                 const char* name, I32 namlen)
{
    dVAR;
    MAGIC* mg;

    if (SvTYPE(sv) < SVt_PVMG) {
        SvUPGRADE(sv, SVt_PVMG);
    }
    Newxz(mg, 1, MAGIC);
    mg->mg_moremagic = SvMAGIC(sv);
    SvMAGIC_set(sv, mg);

    /* Sometimes a magic contains a reference loop, where the sv and
       object refer to each other.  To prevent a reference loop that
       would prevent such objects being freed, we look for such loops
       and if we find one we avoid incrementing the object refcount.

       Note we cannot do this to avoid self-tie loops as intervening RV must
       have its REFCNT incremented to keep it in existence.

    */
    if (!obj || obj == sv ||
        how == PERL_MAGIC_arylen ||
        how == PERL_MAGIC_qr ||
        how == PERL_MAGIC_symtab ||
        (SvTYPE(obj) == SVt_PVGV &&
            (GvSV(obj) == sv || GvHV(obj) == (HV*)sv || GvAV(obj) == (AV*)sv ||
            GvCV(obj) == (CV*)sv || GvIOp(obj) == (IO*)sv ||
            GvFORM(obj) == (CV*)sv)))
    {
        mg->mg_obj = obj;
    }
    else {
        mg->mg_obj = SvREFCNT_inc_simple(obj);
        mg->mg_flags |= MGf_REFCOUNTED;
    }

    /* Normal self-ties simply pass a null object, and instead of
       using mg_obj directly, use the SvTIED_obj macro to produce a
       new RV as needed.  For glob "self-ties", we are tieing the PVIO
       with an RV obj pointing to the glob containing the PVIO.  In
       this case, to avoid a reference loop, we need to weaken the
       reference.
    */

    if (how == PERL_MAGIC_tiedscalar && SvTYPE(sv) == SVt_PVIO &&
        obj && SvROK(obj) && GvIO(SvRV(obj)) == (IO*)sv)
    {
      sv_rvweaken(obj);
    }

    mg->mg_type = how;
    mg->mg_len = namlen;
    if (name) {
        if (namlen > 0)
            mg->mg_ptr = savepvn(name, namlen);
        else if (namlen == HEf_SVKEY)
            mg->mg_ptr = (char*)SvREFCNT_inc_simple_NN((SV*)name);
        else
            mg->mg_ptr = (char *) name;
    }
    mg->mg_virtual = (MGVTBL *) vtable;

    mg_magical(sv);
    if (SvGMAGICAL(sv))
        SvFLAGS(sv) &= ~(SVf_IOK|SVf_NOK|SVf_POK);
    return mg;
}

/*
=for apidoc sv_magic

Adds magic to an SV. First upgrades C<sv> to type C<SVt_PVMG> if necessary,
then adds a new magic item of type C<how> to the head of the magic list.

See C<sv_magicext> (which C<sv_magic> now calls) for a description of the
handling of the C<name> and C<namlen> arguments.

You need to use C<sv_magicext> to add magic to SvREADONLY SVs and also
to add more than one instance of the same 'how'.

=cut
*/

void
Perl_sv_magic(pTHX_ register SV *sv, SV *obj, int how, const char *name, I32 namlen)
{
    dVAR;
    const MGVTBL *vtable;
    MAGIC* mg;

#ifdef PERL_OLD_COPY_ON_WRITE
    if (SvIsCOW(sv))
        sv_force_normal_flags(sv, 0);
#endif
    if (SvREADONLY(sv)) {
        if (
            /* its okay to attach magic to shared strings; the subsequent
             * upgrade to PVMG will unshare the string */
            !(SvFAKE(sv) && SvTYPE(sv) < SVt_PVMG)

            && IN_PERL_RUNTIME
            && how != PERL_MAGIC_regex_global
            && how != PERL_MAGIC_bm
            && how != PERL_MAGIC_fm
            && how != PERL_MAGIC_sv
            && how != PERL_MAGIC_backref
           )
        {
            Perl_croak(aTHX_ PL_no_modify);
        }
    }
    if (SvMAGICAL(sv) || (how == PERL_MAGIC_taint && SvTYPE(sv) >= SVt_PVMG)) {
        if (SvMAGIC(sv) && (mg = mg_find(sv, how))) {
            /* sv_magic() refuses to add a magic of the same 'how' as an
               existing one
             */
            if (how == PERL_MAGIC_taint) {
                mg->mg_len |= 1;
                /* Any scalar which already had taint magic on which someone
                   (erroneously?) did SvIOK_on() or similar will now be
                   incorrectly sporting public "OK" flags.  */
                SvFLAGS(sv) &= ~(SVf_IOK|SVf_NOK|SVf_POK);
            }
            return;
        }
    }

    switch (how) {
    case PERL_MAGIC_sv:
        vtable = &PL_vtbl_sv;
        break;
    case PERL_MAGIC_overload:
        vtable = &PL_vtbl_amagic;
        break;
    case PERL_MAGIC_overload_elem:
        vtable = &PL_vtbl_amagicelem;
        break;
    case PERL_MAGIC_overload_table:
        vtable = &PL_vtbl_ovrld;
        break;
    case PERL_MAGIC_bm:
        vtable = &PL_vtbl_bm;
        break;
    case PERL_MAGIC_regdata:
        vtable = &PL_vtbl_regdata;
        break;
    case PERL_MAGIC_regdata_names:
        vtable = &PL_vtbl_regdata_names;
        break;
    case PERL_MAGIC_regdatum:
        vtable = &PL_vtbl_regdatum;
        break;
    case PERL_MAGIC_env:
        vtable = &PL_vtbl_env;
        break;
    case PERL_MAGIC_fm:
        vtable = &PL_vtbl_fm;
        break;
    case PERL_MAGIC_envelem:
        vtable = &PL_vtbl_envelem;
        break;
    case PERL_MAGIC_regex_global:
        vtable = &PL_vtbl_mglob;
        break;
    case PERL_MAGIC_isa:
        vtable = &PL_vtbl_isa;
        break;
    case PERL_MAGIC_isaelem:
        vtable = &PL_vtbl_isaelem;
        break;
    case PERL_MAGIC_nkeys:
        vtable = &PL_vtbl_nkeys;
        break;
    case PERL_MAGIC_dbfile:
        vtable = NULL;
        break;
    case PERL_MAGIC_dbline:
        vtable = &PL_vtbl_dbline;
        break;
#ifdef USE_LOCALE_COLLATE
    case PERL_MAGIC_collxfrm:
        vtable = &PL_vtbl_collxfrm;
        break;
#endif /* USE_LOCALE_COLLATE */
    case PERL_MAGIC_tied:
        vtable = &PL_vtbl_pack;
        break;
    case PERL_MAGIC_tiedelem:
    case PERL_MAGIC_tiedscalar:
        vtable = &PL_vtbl_packelem;
        break;
    case PERL_MAGIC_qr:
        vtable = &PL_vtbl_regexp;
        break;
    case PERL_MAGIC_hints:
        /* As this vtable is all NULL, we can reuse it.  */
    case PERL_MAGIC_sig:
        vtable = &PL_vtbl_sig;
        break;
    case PERL_MAGIC_sigelem:
        vtable = &PL_vtbl_sigelem;
        break;
    case PERL_MAGIC_taint:
        vtable = &PL_vtbl_taint;
        break;
    case PERL_MAGIC_uvar:
        vtable = &PL_vtbl_uvar;
        break;
    case PERL_MAGIC_vec:
        vtable = &PL_vtbl_vec;
        break;
    case PERL_MAGIC_arylen_p:
    case PERL_MAGIC_rhash:
    case PERL_MAGIC_symtab:
    case PERL_MAGIC_vstring:
        vtable = NULL;
        break;
    case PERL_MAGIC_utf8:
        vtable = &PL_vtbl_utf8;
        break;
    case PERL_MAGIC_substr:
        vtable = &PL_vtbl_substr;
        break;
    case PERL_MAGIC_defelem:
        vtable = &PL_vtbl_defelem;
        break;
    case PERL_MAGIC_arylen:
        vtable = &PL_vtbl_arylen;
        break;
    case PERL_MAGIC_pos:
        vtable = &PL_vtbl_pos;
        break;
    case PERL_MAGIC_backref:
        vtable = &PL_vtbl_backref;
        break;
    case PERL_MAGIC_hintselem:
        vtable = &PL_vtbl_hintselem;
        break;
    case PERL_MAGIC_ext:
        /* Reserved for use by extensions not perl internals.           */
        /* Useful for attaching extension internal data to perl vars.   */
        /* Note that multiple extensions may clash if magical scalars   */
        /* etc holding private data from one are passed to another.     */
        vtable = NULL;
        break;
    default:
        Perl_croak(aTHX_ "Don't know how to handle magic of type \\%o", how);
    }

    /* Rest of work is done else where */
    mg = sv_magicext(sv,obj,how,vtable,name,namlen);

    switch (how) {
    case PERL_MAGIC_taint:
        mg->mg_len = 1;
        break;
    case PERL_MAGIC_ext:
    case PERL_MAGIC_dbfile:
        SvRMAGICAL_on(sv);
        break;
    }
}

/*
=for apidoc sv_unmagic

Removes all magic of type C<type> from an SV.

=cut
*/

int
Perl_sv_unmagic(pTHX_ SV *sv, int type)
{
    MAGIC* mg;
    MAGIC** mgp;
    if (SvTYPE(sv) < SVt_PVMG || !SvMAGIC(sv))
        return 0;
    mgp = &(((XPVMG*) SvANY(sv))->xmg_u.xmg_magic);
    for (mg = *mgp; mg; mg = *mgp) {
        if (mg->mg_type == type) {
            const MGVTBL* const vtbl = mg->mg_virtual;
            *mgp = mg->mg_moremagic;
            if (vtbl && vtbl->svt_free)
                CALL_FPTR(vtbl->svt_free)(aTHX_ sv, mg);
            if (mg->mg_ptr && mg->mg_type != PERL_MAGIC_regex_global) {
                if (mg->mg_len > 0)
                    Safefree(mg->mg_ptr);
                else if (mg->mg_len == HEf_SVKEY)
                    SvREFCNT_dec((SV*)mg->mg_ptr);
                else if (mg->mg_type == PERL_MAGIC_utf8)
                    Safefree(mg->mg_ptr);
            }
            if (mg->mg_flags & MGf_REFCOUNTED)
                SvREFCNT_dec(mg->mg_obj);
            Safefree(mg);
        }
        else
            mgp = &mg->mg_moremagic;
    }
    if (!SvMAGIC(sv)) {
        SvMAGICAL_off(sv);
        SvFLAGS(sv) |= (SvFLAGS(sv) & (SVp_IOK|SVp_NOK|SVp_POK)) >> PRIVSHIFT;
        SvMAGIC_set(sv, NULL);
    }

    return 0;
}

/*
=for apidoc sv_rvweaken

Weaken a reference: set the C<SvWEAKREF> flag on this RV; give the
referred-to SV C<PERL_MAGIC_backref> magic if it hasn't already; and
push a back-reference to this RV onto the array of backreferences
associated with that magic. If the RV is magical, set magic will be
called after the RV is cleared.

=cut
*/

SV *
Perl_sv_rvweaken(pTHX_ SV *sv)
{
    SV *tsv;
    if (!SvOK(sv))  /* let undefs pass */
        return sv;
    if (!SvROK(sv))
        Perl_croak(aTHX_ "Can't weaken a nonreference");
    else if (SvWEAKREF(sv)) {
        if (ckWARN(WARN_MISC))
            Perl_warner(aTHX_ packWARN(WARN_MISC), "Reference is already weak");
        return sv;
    }
    tsv = SvRV(sv);
    Perl_sv_add_backref(aTHX_ tsv, sv);
    SvWEAKREF_on(sv);
    SvREFCNT_dec(tsv);
    return sv;
}

/* Give tsv backref magic if it hasn't already got it, then push a
 * back-reference to sv onto the array associated with the backref magic.
 */

void
Perl_sv_add_backref(pTHX_ SV *tsv, SV *sv)
{
    dVAR;
    AV *av;

    if (SvTYPE(tsv) == SVt_PVHV) {
        AV **const avp = Perl_hv_backreferences_p(aTHX_ (HV*)tsv);

        av = *avp;
        if (!av) {
            /* There is no AV in the offical place - try a fixup.  */
            MAGIC *const mg = mg_find(tsv, PERL_MAGIC_backref);

            if (mg) {
                /* Aha. They've got it stowed in magic.  Bring it back.  */
                av = (AV*)mg->mg_obj;
                /* Stop mg_free decreasing the refernce count.  */
                mg->mg_obj = NULL;
                /* Stop mg_free even calling the destructor, given that
                   there's no AV to free up.  */
                mg->mg_virtual = 0;
                sv_unmagic(tsv, PERL_MAGIC_backref);
            } else {
                av = newAV();
                AvREAL_off(av);
                SvREFCNT_inc_simple_void(av);
            }
            *avp = av;
        }
    } else {
        const MAGIC *const mg
            = SvMAGICAL(tsv) ? mg_find(tsv, PERL_MAGIC_backref) : NULL;
        if (mg)
            av = (AV*)mg->mg_obj;
        else {
            av = newAV();
            AvREAL_off(av);
            sv_magic(tsv, (SV*)av, PERL_MAGIC_backref, NULL, 0);
            /* av now has a refcnt of 2, which avoids it getting freed
             * before us during global cleanup. The extra ref is removed
             * by magic_killbackrefs() when tsv is being freed */
        }
    }
    if (AvFILLp(av) >= AvMAX(av)) {
        av_extend(av, AvFILLp(av)+1);
    }
    AvARRAY(av)[++AvFILLp(av)] = sv; /* av_push() */
}

/* delete a back-reference to ourselves from the backref magic associated
 * with the SV we point to.
 */

STATIC void
S_sv_del_backref(pTHX_ SV *tsv, SV *sv)
{
    dVAR;
    AV *av = NULL;
    SV **svp;
 &