Re: [PATCH] s/Null(gv|hv|sv)/NULL/g

[perl5.git] / sv.c

/*    sv.c
 *
 *    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
 *    2000, 2001, 2002, 2003, 2004, 2005, 2006, 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
/* The cache element 0 is the Unicode offset;
 * the cache element 1 is the byte offset of the element 0;
 * the cache element 2 is the Unicode length of the substring;
 * the cache element 3 is the byte length of the substring;
 * The checking of the substring side would be good
 * but substr() has enough code paths to make my head spin;
 * 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]); } } 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, as well as a
pointer to the body (struct xrv, xpv, xpviv...), which contains fields
specific to each type.

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

The first slot in each arena is reserved, and is used to hold a link
to the next arena.  In the case of heads, the unused first slot also
contains 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.

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_arenaroots[]  array of pointers to list of arenas, 1 per svtype
    PL_body_roots[]       array of pointers to list of free bodies of svtype
                          arrays are indexed by the svtype needed

Note that some of the larger and more rarely used body types (eg
xpvio) are not allocated using arenas, but are instead just
malloc()/free()ed as required.

In addition, a few SV heads are not allocated from an arena, but are
instead directly created as static or auto variables, 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.

Similarly, there are macros new_XIV()/del_XIV(), new_XNV()/del_XNV() etc
that allocate and return individual body types. Normally these are mapped
to the arena-manipulating functions new_xiv()/del_xiv() etc, but may be
instead mapped directly to malloc()/free() if PURIFY is defined. The
new/del functions remove from, or add to, the appropriate PL_foo_root
list, and call more_xiv() etc to add a new arena if the list is empty.

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)    Poison(sv, 1, struct STRUCT_SV)
*/
#  define POSION_SV_HEAD(sv)    Poison(&SvANY(sv), 1, void *), \
                                Poison(&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);
#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 && 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(SV**);
    }
    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;
}

static void 
S_free_arena(pTHX_ void **root) {
    while (root) {
        void ** const next = *(void **)root;
        Safefree(root);
        root = next;
    }
}
    
/*
=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);
    }

    S_free_arena(aTHX_ (void**) PL_body_arenas);

    for (i=0; i<SVt_LAST; 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)
*/

STATIC void *
S_more_bodies (pTHX_ size_t size, svtype sv_type)
{
    dVAR;
    void ** const root = &PL_body_roots[sv_type];
    char *start;
    const char *end;
    const size_t count = PERL_ARENA_SIZE / size;

    Newx(start, count*size, char);
    *((void **) start) = PL_body_arenas;
    PL_body_arenas = (void *)start;

    end = start + (count-1) * size;

    /* The initial slot is used to link the arenas together, so it isn't to be
       linked into the list of ready-to-use bodies.  */

    start += size;

    *root = (void *)start;

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

    return *root;
}

/* grab a new thing from the free list, allocating more if necessary */

/* 1st, the inline version  */

#define new_body_inline(xpv, size, sv_type) \
    STMT_START { \
        void ** const r3wt = &PL_body_roots[sv_type]; \
        LOCK_SV_MUTEX; \
        xpv = *((void **)(r3wt)) \
          ? *((void **)(r3wt)) : S_more_bodies(aTHX_ size, sv_type); \
        *(r3wt) = *(void**)(xpv); \
        UNLOCK_SV_MUTEX; \
    } STMT_END

/* now use the inline version in the proper function */

#ifndef PURIFY

/* This isn't being used with -DPURIFY, so don't declare it. Otherwise
   compilers issue warnings.  */

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

#endif

/* 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

/* 
   Revisiting type 3 arenas, there are 4 body-types which have some
   members that are never accessed.  They are XPV, XPVIV, XPVAV,
   XPVHV, which have corresponding types: xpv_allocated,
   xpviv_allocated, xpvav_allocated, xpvhv_allocated,

   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.  */

/* The following 2 arrays hide the above details in a pair of
   lookup-tables, allowing us to be body-type agnostic.

   size maps svtype to its body's allocated size.
   offset maps svtype to the body-pointer adjustment needed

   NB: elements in latter are 0 or <0, and are added during
   allocation, and subtracted during deallocation.  It may be clearer
   to invert the values, and call it shrinkage_by_svtype.
*/

struct body_details {
    size_t size;        /* Size to allocate  */
    size_t copy;        /* Size of structure to copy (may be shorter)  */
    size_t offset;
    bool cant_upgrade;  /* Can upgrade this type */
    bool zero_nv;       /* zero the NV when upgrading from this */
    bool arena;         /* Allocated from an arena */
};

#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

/* 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[] = {
    {0, 0, 0, FALSE, NONV, NOARENA},
    /* IVs are in the head, so the allocation size is 0  */
    {0, sizeof(IV), STRUCT_OFFSET(XPVIV, xiv_iv), FALSE, NONV, NOARENA},
    /* 8 bytes on most ILP32 with IEEE doubles */
    {sizeof(NV), sizeof(NV), 0, FALSE, HADNV, HASARENA},
    /* RVs are in the head now */
    /* However, this slot is overloaded and used by the pte  */
    {0, 0, 0, FALSE, NONV, NOARENA},
    /* 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),
     FALSE, NONV, HASARENA},
    /* 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),
     FALSE, NONV, HASARENA},
    /* 20 */
    {sizeof(XPVNV), copy_length(XPVNV, xiv_u), 0, FALSE, HADNV, HASARENA},
    /* 28 */
    {sizeof(XPVMG), copy_length(XPVMG, xmg_stash), 0, FALSE, HADNV, HASARENA},
    /* 36 */
    {sizeof(XPVBM), sizeof(XPVBM), 0, TRUE, HADNV, HASARENA},
    /* 48 */
    {sizeof(XPVGV), sizeof(XPVGV), 0, TRUE, HADNV, HASARENA},
    /* 64 */
    {sizeof(XPVLV), sizeof(XPVLV), 0, TRUE, HADNV, HASARENA},
    /* 20 */
    {sizeof(xpvav_allocated),
     copy_length(XPVAV, xmg_stash)
     - relative_STRUCT_OFFSET(xpvav_allocated, XPVAV, xav_fill),
     + relative_STRUCT_OFFSET(xpvav_allocated, XPVAV, xav_fill),
     TRUE, HADNV, HASARENA},
    /* 20 */
    {sizeof(xpvhv_allocated),
     copy_length(XPVHV, xmg_stash)
     - relative_STRUCT_OFFSET(xpvhv_allocated, XPVHV, xhv_fill),
     + relative_STRUCT_OFFSET(xpvhv_allocated, XPVHV, xhv_fill),
     TRUE, HADNV, HASARENA},
    /* 76 */
    {sizeof(XPVCV), sizeof(XPVCV), 0, TRUE, HADNV, HASARENA},
    /* 80 */
    {sizeof(XPVFM), sizeof(XPVFM), 0, TRUE, HADNV, NOARENA},
    /* 84 */
    {sizeof(XPVIO), sizeof(XPVIO), 0, TRUE, HADNV, NOARENA}
};

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

#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_ bodies_by_type[sv_type].size, 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)->size + (details)->offset)
#define new_NOARENAZ(details) \
        my_safecalloc((details)->size + (details)->offset)

/*
=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, U32 new_type)
{
    dVAR;
    void*       old_body;
    void*       new_body;
    const U32   old_type = SvTYPE(sv);
    const struct body_details *const old_type_details
        = bodies_by_type + old_type;
    const struct body_details *new_type_details = bodies_by_type + new_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)

       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;
            new_type_details = bodies_by_type + new_type;
        }
        break;
    case SVt_NV:
        if (new_type < SVt_PVNV) {
            new_type = SVt_PVNV;
            new_type_details = bodies_by_type + new_type;
        }
        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((SvFLAGS(sv) & SVpad_TYPED) == 0);
        break;
    default:
        if (old_type_details->cant_upgrade)
            Perl_croak(aTHX_ "Can't upgrade that kind of scalar");
    }

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

    switch (new_type) {
    case SVt_NULL:
        Perl_croak(aTHX_ "Can't upgrade to undef");
    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:
        SvANY(sv) = new_XPVHV();
        HvFILL(sv)      = 0;
        HvMAX(sv)       = 0;
        HvTOTALKEYS(sv) = 0;

        goto hv_av_common;

    case SVt_PVAV:
        SvANY(sv) = new_XPVAV();
        AvMAX(sv)       = -1;
        AvFILLp(sv)     = -1;
        AvALLOC(sv)     = 0;
        AvREAL_only(sv);

    hv_av_common:
        /* 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);
        }

        /* Could put this in the else clause below, as PVMG must have SvPVX
           0 already (the assertion above)  */
        SvPV_set(sv, NULL);

        if (old_type >= SVt_PVMG) {
            SvMAGIC_set(sv, ((XPVMG*)old_body)->xmg_magic);
            SvSTASH_set(sv, ((XPVMG*)old_body)->xmg_stash);
        } else {
            SvMAGIC_set(sv, NULL);
            SvSTASH_set(sv, NULL);
        }
        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_PVBM:
    case SVt_PVGV:
    case SVt_PVCV:
    case SVt_PVLV:
    case SVt_PVMG:
    case SVt_PVNV:
    case SVt_PV:

        assert(new_type_details->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_details->size, new_type);
            Zero(new_body, new_type_details->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) {
            Copy((char *)old_body + old_type_details->offset,
                 (char *)new_body + old_type_details->offset,
                 old_type_details->copy, 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->size) {
        /* If the old body had an allocated size, then we need to free it.  */
#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)
{
    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;

#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 = saferealloc(s, newlen);
        }
        else {
            s = 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));
    }
    (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_setiv(sv, 0);
    SvIsUV_on(sv);
    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));
    }
    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);
}

/* 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;
    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 (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 {
                    /* 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 {
                        /* 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 (!(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)) {
        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)) {
        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)) {
        mg_get(sv);
        if (SvNOKp(sv))
            return SvNVX(sv);
        if (SvPOKp(sv) && SvLEN(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 (!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;
}

/* stringify_regexp(): private routine for use by sv_2pv_flags(): converts
 * a regexp to its stringified form.
 */

static char *
S_stringify_regexp(pTHX_ SV *sv, MAGIC *mg, STRLEN *lp) {
    dVAR;
    const regexp * const re = (regexp *)mg->mg_obj;

    if (!mg->mg_ptr) {
        const char *fptr = "msix";
        char reflags[6];
        char ch;
        int left = 0;
        int right = 4;
        bool need_newline = 0;
        U16 reganch = (U16)((re->reganch & PMf_COMPILETIME) >> 12);

        while((ch = *fptr++)) {
            if(reganch & 1) {
                reflags[left++] = ch;
            }
            else {
                reflags[right--] = ch;
            }
            reganch >>= 1;
        }
        if(left != 4) {
            reflags[left] = '-';
            left = 5;
        }

        mg->mg_len = re->prelen + 4 + left;
        /*
         * If /x was used, we have to worry about a regex ending with a
         * comment later being embedded within another regex. If so, we don't
         * want this regex's "commentization" to leak out to the right part of
         * the enclosing regex, we must cap it with a newline.
         *
         * So, if /x was used, we scan backwards from the end of the regex. If
         * we find a '#' before we find a newline, we need to add a newline
         * ourself. If we find a '\n' first (or if we don't find '#' or '\n'),
         * we don't need to add anything.  -jfriedl
         */
        if (PMf_EXTENDED & re->reganch) {
            const char *endptr = re->precomp + re->prelen;
            while (endptr >= re->precomp) {
                const char c = *(endptr--);
                if (c == '\n')
                    break; /* don't need another */
                if (c == '#') {
                    /* we end while in a comment, so we need a newline */
                    mg->mg_len++; /* save space for it */
                    need_newline = 1; /* note to add it */
                    break;
                }
            }
        }

        Newx(mg->mg_ptr, mg->mg_len + 1 + left, char);
        mg->mg_ptr[0] = '(';
        mg->mg_ptr[1] = '?';
        Copy(reflags, mg->mg_ptr+2, left, char);
        *(mg->mg_ptr+left+2) = ':';
        Copy(re->precomp, mg->mg_ptr+3+left, re->prelen, char);
        if (need_newline)
            mg->mg_ptr[mg->mg_len - 2] = '\n';
        mg->mg_ptr[mg->mg_len - 1] = ')';
        mg->mg_ptr[mg->mg_len] = 0;
    }
    PL_reginterp_cnt += re->program[0].next_off;
    
    if (re->reganch & ROPT_UTF8)
        SvUTF8_on(sv);
    else
        SvUTF8_off(sv);
    if (lp)
        *lp = mg->mg_len;
    return mg->mg_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_sprintf(tbuf,"%"UVuf, (UV)SvUVX(sv))
                    : my_sprintf(tbuf,"%"IVdf, (IV)SvIVX(sv));
            } else {
                Gconvert(SvNVX(sv), NV_DIG, 0, tbuf);
                len = strlen(tbuf);
            }
            if (SvROK(sv)) {    /* XXX Skip this when sv_pvn_force calls */
                /* Sneaky stuff here */
                SV * const tsv = newSVpvn(tbuf, len);

                sv_2mortal(tsv);
                if (lp)
                    *lp = SvCUR(tsv);
                return SvPVX(tsv);
            }
            else {
                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 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;
                }
            }
            {
                SV *tsv;
                MAGIC *mg;
                const SV *const referent = (SV*)SvRV(sv);

                if (!referent) {
                    tsv = sv_2mortal(newSVpvs("NULLREF"));
                } 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))) {
                    return stringify_regexp(sv, mg, lp);
                } else {
                    const char *const typestr = sv_reftype(referent, 0);

                    tsv = sv_newmortal();
                    if (SvOBJECT(referent)) {
                        const char *const name = HvNAME_get(SvSTASH(referent));
                        Perl_sv_setpvf(aTHX_ tsv, "%s=%s(0x%"UVxf")",
                                       name ? name : "__ANON__" , typestr,
                                       PTR2UV(referent));
                    }
                    else
                        Perl_sv_setpvf(aTHX_ tsv, "%s(0x%"UVxf")", typestr,
                                       PTR2UV(referent));
                }
                if (lp)
                    *lp = SvCUR(tsv);
                return SvPVX(tsv);
            }
        }
        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 isIOK = SvIOK(sv);
        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';
        if (isIOK)
            SvIOK_on(sv);
        else
            SvIOKp_on(sv);
        if (isUIOK)
            SvIsUV_on(sv);
    }
    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)
            (void)strcpy(s,"0");
        else
#endif /*apollo*/
        {
            Gconvert(SvNVX(sv), NV_DIG, 0, s);
        }
        errno = olderrno;
#ifdef FIXNEGATIVEZERO
        if (*s == '-' && s[1] == '0' && !s[2])
            strcpy(s,"0");
#endif
        while (*s) s++;
#ifdef hcx
        if (s[-1] == '.')
            *--s = '\0';
#endif
    }
    else {
        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
                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)
{
    (void) sv_utf8_upgrade(sv);
    if (SvIsCOW(sv)) {
        sv_force_normal_flags(sv, 0);
    }
    if (SvREADONLY(sv)) {
        Perl_croak(aTHX_ PL_no_modify);
    }
    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(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)
            sv_upgrade(dstr, SVt_PVGV);
        sv_magic(dstr, dstr, PERL_MAGIC_glob, NULL, 0);
        GvSTASH(dstr) = GvSTASH(sstr);
        if (GvSTASH(dstr))
            Perl_sv_add_backref(aTHX_ (SV*)GvSTASH(dstr), dstr);
        GvNAME(dstr) = savepvn(name, len);
        GvNAMELEN(dstr) = len;
        SvFAKE_on(dstr);        /* can coerce to non-glob */
    }

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

    (void)SvOK_off(dstr);
    GvINTRO_off(dstr);          /* one-shot flag */
    gp_free((GV*)dstr);
    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_pvgv_assign(pTHX_ SV *dstr, SV *sstr) {
    SV * const sref = SvREFCNT_inc(SvRV(sstr));
    SV *dref = NULL;
    const int intro = GvINTRO(dstr);

#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 (SvTYPE(sref)) {
    case SVt_PVAV:
        if (intro)
            SAVEGENERICSV(GvAV(dstr));
        else
            dref = (SV*)GvAV(dstr);
        GvAV(dstr) = (AV*)sref;
        if (!GvIMPORTED_AV(dstr)
            && CopSTASH_ne(PL_curcop, GvSTASH(dstr)))
            {
                GvIMPORTED_AV_on(dstr);
            }
        break;
    case SVt_PVHV:
        if (intro)
            SAVEGENERICSV(GvHV(dstr));
        else
            dref = (SV*)GvHV(dstr);
        GvHV(dstr) = (HV*)sref;
        if (!GvIMPORTED_HV(dstr)
            && CopSTASH_ne(PL_curcop, GvSTASH(dstr)))
            {
                GvIMPORTED_HV_on(dstr);
            }
        break;
    case SVt_PVCV:
        if (intro) {
            if (GvCVGEN(dstr) && GvCV(dstr) != (CV*)sref) {
                SvREFCNT_dec(GvCV(dstr));
                GvCV(dstr) = NULL;
                GvCVGEN(dstr) = 0; /* Switch off cacheness. */
                PL_sub_generation++;
            }
            SAVEGENERICSV(GvCV(dstr));
        }
        else
            dref = (SV*)GvCV(dstr);
        if (GvCV(dstr) != (CV*)sref) {
            CV* const cv = GvCV(dstr);
            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)) {
                            /* 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),
                                        CvCONST(cv)
                                        ? "Constant subroutine %s::%s redefined"
                                        : "Subroutine %s::%s redefined",
                                        HvNAME_get(GvSTASH((GV*)dstr)),
                                        GvENAME((GV*)dstr));
                        }
                    }
                if (!intro)
                    cv_ckproto(cv, (GV*)dstr,
                               SvPOK(sref) ? SvPVX_const(sref) : NULL);
            }
            GvCV(dstr) = (CV*)sref;
            GvCVGEN(dstr) = 0; /* Switch off cacheness. */
            GvASSUMECV_on(dstr);
            PL_sub_generation++;
        }
        if (!GvIMPORTED_CV(dstr) && CopSTASH_ne(PL_curcop, GvSTASH(dstr))) {
            GvIMPORTED_CV_on(dstr);
        }
        break;
    case SVt_PVIO:
        if (intro)
            SAVEGENERICSV(GvIOp(dstr));
        else
            dref = (SV*)GvIOp(dstr);
        GvIOp(dstr) = (IO*)sref;
        break;
    case SVt_PVFM:
        if (intro)
            SAVEGENERICSV(GvFORM(dstr));
        else
            dref = (SV*)GvFORM(dstr);
        GvFORM(dstr) = (CV*)sref;
        break;
    default:
        if (intro)
            SAVEGENERICSV(GvSV(dstr));
        else
            dref = (SV*)GvSV(dstr);
        GvSV(dstr) = sref;
        if (!GvIMPORTED_SV(dstr) && CopSTASH_ne(PL_curcop, GvSTASH(dstr))) {
            GvIMPORTED_SV_on(dstr);
        }
        break;
    }
    if (dref)
        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 int stype;

    if (sstr == dstr)
        return;
    SV_CHECK_THINKFIRST_COW_DROP(dstr);
    if (!sstr)
        sstr = &PL_sv_undef;
    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:
                sv_upgrade(dstr, SVt_PVNV);
                break;
            case SVt_RV:
            case SVt_PV:
                sv_upgrade(dstr, SVt_PVIV);
                break;
            }
            (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;
            }
            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);
        else if (dtype == SVt_PVGV &&
                 SvROK(sstr) && 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;
            }
            S_glob_assign(aTHX_ dstr, sstr, dtype);
            return;
        }
        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;
    case SVt_PVAV:
    case SVt_PVHV:
    case SVt_PVCV:
    case SVt_PVIO:
        {
        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_PVGV:
        if (dtype <= SVt_PVGV) {
            S_glob_assign(aTHX_ dstr, sstr, dtype);
            return;
        }
        /* FALL THROUGH */

    default:
        if (SvGMAGICAL(sstr) && (flags & SV_GMAGIC)) {
            mg_get(sstr);
            if ((int)SvTYPE(sstr) != stype) {
                stype = SvTYPE(sstr);
                if (stype == SVt_PVGV && dtype <= SVt_PVGV) {
                    S_glob_assign(aTHX_ dstr, sstr, dtype);
                    return;
                }
            }
        }
        if (stype == SVt_PVLV)
            SvUPGRADE(dstr, SVt_PVNV);
        else
            SvUPGRADE(dstr, (U32)stype);
    }

    sflags = SvFLAGS(sstr);

    if (sflags & SVf_ROK) {
        if (dtype >= SVt_PV) {
            if (dtype == SVt_PVGV) {
                S_pvgv_assign(aTHX_ 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|SVf_AMAGIC);
        assert(!(sflags & SVp_NOK));
        assert(!(sflags & SVp_IOK));
        assert(!(sflags & SVf_NOK));
        assert(!(sflags & SVf_IOK));
    }
    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.
         */

        /* 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 (
            /* We're not already COW  */
            ((sflags & (SVf_FAKE | SVf_READONLY)) != (SVf_FAKE | SVf_READONLY)
#ifndef PERL_OLD_COPY_ON_WRITE
             /* or we are, but dstr isn't a suitable target.  */
             || (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 = SvVOK(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) {
            SvFLAGS(dstr) |= sflags & (SVf_NOK|SVp_NOK);
            SvNV_set(dstr, SvNVX(sstr));
        }
    }
    else {
        if (dtype == SVt_PVGV) {
            if (ckWARN(WARN_MISC))
                Perl_warner(aTHX_ packWARN(WARN_MISC), "Undefined value assigned to typeglob");
        }
        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

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.  This function will realloc 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.  Does not handle 'set' magic.
See C<sv_usepvn_mg>.

=cut
*/

void
Perl_sv_usepvn(pTHX_ register SV *sv, register char *ptr, register STRLEN len)
{
    dVAR;
    STRLEN allocate;
    SV_CHECK_THINKFIRST_COW_DROP(sv);
    SvUPGRADE(sv, SVt_PV);
    if (!ptr) {
        (void)SvOK_off(sv);
        return;
    }
    if (SvPVX_const(sv))
        SvPV_free(sv);

    allocate = PERL_STRLEN_ROUNDUP(len + 1);
    ptr = saferealloc (ptr, allocate);
    SvPV_set(sv, ptr);
    SvCUR_set(sv, len);
    SvLEN_set(sv, allocate);
    *SvEND(sv) = '\0';
    (void)SvPOK_only_UTF8(sv);          /* validate pointer */
    SvTAINT(sv);
}

/*
=for apidoc sv_usepvn_mg

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

=cut
*/

void
Perl_sv_usepvn_mg(pTHX_ register SV *sv, register char *ptr, register STRLEN len)
{
    sv_usepvn(sv,ptr,len);
    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, 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(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((SV*)name);
        else
            mg->mg_ptr = (char *) name;
    }
    mg->mg_virtual = 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;
    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;
            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_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_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_glob:
        vtable = &PL_vtbl_glob;
        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_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 = &SvMAGIC(sv);
    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 && mg->mg_ptr)
                    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_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.

=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(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;
    I32 i;

    if (SvTYPE(tsv) == SVt_PVHV && SvOOK(tsv)) {
        av = *Perl_hv_backreferences_p(aTHX_ (HV*)tsv);
        /* We mustn't attempt to "fix up" the hash here by moving the
           backreference array back to the hv_aux structure, as that is stored
           in the main HvARRAY(), and hfreentries assumes that no-one
           reallocates HvARRAY() while it is running.  */
    }
    if (!av) {
        const MAGIC *const mg
            = SvMAGICAL(tsv) ? mg_find(tsv, PERL_MAGIC_backref) : NULL;
        if (mg)
            av = (AV *)mg->mg_obj;
    }
    if (!av) {
        if (PL_in_clean_all)
            return;
        Perl_croak(aTHX_ "panic: del_backref");
    }

    if (SvIS_FREED(av))
        return;

    svp = AvARRAY(av);
    /* We shouldn't be in here more than once, but for paranoia reasons lets
       not assume this.  */
    for (i = AvFILLp(av); i >= 0; i--) {
        if (svp[i] == sv) {
            const SSize_t fill = AvFILLp(av);
            if (i != fill) {
                /* We weren't the last entry.
                   An unordered list has this property that you can take the
                   last element off the end to fill the hole, and it's still
                   an unordered list :-)
                */
                svp[i] = svp[fill];
            }
            svp[fill] = NULL;
            AvFILLp(av) = fill - 1;
        }
    }
}

int
Perl_sv_kill_backrefs(pTHX_ SV *sv, AV *av)
{
    SV **svp = AvARRAY(av);

    PERL_UNUSED_ARG(sv);

    /* Not sure why the av can get freed ahead of its sv, but somehow it does
       in ext/B/t/bytecode.t test 15 (involving print <DATA>)  */
    if (svp && !SvIS_FREED(av)) {
        SV *const *const last = svp + AvFILLp(av);

        while (svp <= last) {
            if (*svp) {
                SV *const referrer = *svp;
                if (SvWEAKREF(referrer)) {
                    /* XXX Should we check that it hasn't changed? */
                    SvRV_set(referrer, 0);
                    SvOK_off(referrer);
                    SvWEAKREF_off(referrer);
                } else if (SvTYPE(referrer) == SVt_PVGV ||
                           SvTYPE(referrer) == SVt_PVLV) {
                    /* You lookin' at me?  */
                    assert(GvSTASH(referrer));
                    assert(GvSTASH(referrer) == (HV*)sv);
                    GvSTASH(referrer) = 0;
                } else {
                    Perl_croak(aTHX_
                               "panic: magic_killbackrefs (flags=%"UVxf")",
                               (UV)SvFLAGS(referrer));
                }

                *svp = NULL;
            }
            svp++;
        }
    }
    SvREFCNT_dec(av); /* remove extra count added by sv_add_backref() */
    return 0;
}

/*
=for apidoc sv_insert

Inserts a string at the specified offset/length within the SV. Similar to
the Perl substr() function.

=cut
*/

void
Perl_sv_insert(pTHX_ SV *bigstr, STRLEN offset, STRLEN len, const char *little, STRLEN littlelen)
{
    dVAR;
    register char *big;
    register char *mid;
    register char *midend;
    register char *bigend;
    register I32 i;
    STRLEN curlen;


    if (!bigstr)
        Perl_croak(aTHX_ "Can't modify non-existent substring");
    SvPV_force(bigstr, curlen);
    (void)SvPOK_only_UTF8(bigstr);
    if (offset + len > curlen) {
        SvGROW(bigstr, offset+len+1);
        Zero(SvPVX(bigstr)+curlen, offset+len-curlen, char);
        SvCUR_set(bigstr, offset+len);
    }

    SvTAINT(bigstr);
    i = littlelen - len;
    if (i > 0) {                        /* string might grow */
        big = SvGROW(bigstr, SvCUR(bigstr) + i + 1);
        mid = big + offset + len;
        midend = bigend = big + SvCUR(bigstr);
        bigend += i;
        *bigend = '\0';
        while (midend > mid)            /* shove everything down */
            *--bigend = *--midend;
        Move(little,big+offset,littlelen,char);
        SvCUR_set(bigstr, SvCUR(bigstr) + i);
        SvSETMAGIC(bigstr);
        return;
    }
    else if (i == 0) {
        Move(little,SvPVX(bigstr)+offset,len,char);
        SvSETMAGIC(bigstr);
        return;
    }

    big = SvPVX(bigstr);
    mid = big + offset;
    midend = mid + len;
    bigend = big + SvCUR(bigstr);

    if (midend > bigend)
        Perl_croak(aTHX_ "panic: sv_insert");

    if (mid - big > bigend - midend) {  /* faster to shorten from end */
        if (littlelen) {
            Move(little, mid, littlelen,char);
            mid += littlelen;
        }
        i = bigend - midend;
        if (i > 0) {
            Move(midend, mid, i,char);
            mid += i;
        }
        *mid = '\0';
        SvCUR_set(bigstr, mid - big);
    }
    else if ((i = mid - big)) { /* faster from front */
        midend -= littlelen;
        mid = midend;
        sv_chop(bigstr,midend-i);
        big += i;
        while (i--)
            *--midend = *--big;
        if (littlelen)
            Move(little, mid, littlelen,char);
    }
    else if (littlelen) {
        midend -= littlelen;
        sv_chop(bigstr,midend);
        Move(little,midend,littlelen,char);
    }
    else {
        sv_chop(bigstr,midend);
    }
    SvSETMAGIC(bigstr);
}

/*
=for apidoc sv_replace

Make the first argument a copy of the second, then delete the original.
The target SV physically takes over ownership of the body of the source SV
and inherits its flags; however, the target keeps any magic it owns,
and any magic in the source is discarded.
Note that this is a rather specialist SV copying operation; most of the
time you'll want to use C<sv_setsv> or one of its many macro front-ends.

=cut
*/

void
Perl_sv_replace(pTHX_ register SV *sv, register SV *nsv)
{
    dVAR;
    const U32 refcnt = SvREFCNT(sv);
    SV_CHECK_THINKFIRST_COW_DROP(sv);
    if (SvREFCNT(nsv) != 1) {
        Perl_croak(aTHX_ "panic: reference miscount on nsv in sv_replace() (%"
                   UVuf " != 1)", (UV) SvREFCNT(nsv));
    }
    if (SvMAGICAL(sv)) {
        if (SvMAGICAL(nsv))
            mg_free(nsv);
        else
            sv_upgrade(nsv, SVt_PVMG);
        SvMAGIC_set(nsv, SvMAGIC(sv));
        SvFLAGS(nsv) |= SvMAGICAL(sv);
        SvMAGICAL_off(sv);
        SvMAGIC_set(sv, NULL);
    }
    SvREFCNT(sv) = 0;
    sv_clear(sv);
    assert(!SvREFCNT(sv));
#ifdef DEBUG_LEAKING_SCALARS
    sv->sv_flags  = nsv->sv_flags;
    sv->sv_any    = nsv->sv_any;
    sv->sv_refcnt = nsv->sv_refcnt;
    sv->sv_u      = nsv->sv_u;
#else
    StructCopy(nsv,sv,SV);
#endif
    /* Currently could join these into one piece of pointer arithmetic, but
       it would be unclear.  */
    if(SvTYPE(sv) == SVt_IV)
        SvANY(sv)
            = (XPVIV*)((char*)&(sv->sv_u.svu_iv) - STRUCT_OFFSET(XPVIV, xiv_iv));
    else if (SvTYPE(sv) == SVt_RV) {
        SvANY(sv) = &sv->sv_u.svu_rv;
    }
        

#ifdef PERL_OLD_COPY_ON_WRITE
    if (SvIsCOW_normal(nsv)) {
        /* We need to follow the pointers around the loop to make the
           previous SV point to sv, rather than nsv.  */
        SV *next;
        SV *current = nsv;
        while ((next = SV_COW_NEXT_SV(current)) != nsv) {
            assert(next);
            current = next;
            assert(SvPVX_const(current) == SvPVX_const(nsv));
        }
        /* Make the SV before us point to the SV after us.  */
        if (DEBUG_C_TEST) {
            PerlIO_printf(Perl_debug_log, "previous is\n");
            sv_dump(current);
            PerlIO_printf(Perl_debug_log,
                          "move it from 0x%"UVxf" to 0x%"UVxf"\n",
                          (UV) SV_COW_NEXT_SV(current), (UV) sv);
        }
        SV_COW_NEXT_SV_SET(current, sv);
    }
#endif
    SvREFCNT(sv) = refcnt;
    SvFLAGS(nsv) |= SVTYPEMASK;         /* Mark as freed */
    SvREFCNT(nsv) = 0;
    del_SV(nsv);
}

/*
=for apidoc sv_clear

Clear an SV: call any destructors, free up any memory used by the body,
and free the body itself. The SV's head is I<not> freed, although
its type is set to all 1's so that it won't inadvertently be assumed
to be live during global destruction etc.
This function should only be called when REFCNT is zero. Most of the time
you'll want to call C<sv_free()> (or its macro wrapper C<SvREFCNT_dec>)
instead.

=cut
*/

void
Perl_sv_clear(pTHX_ register SV *sv)
{
    dVAR;
    const U32 type = SvTYPE(sv);
    const struct body_details *const sv_type_details
        = bodies_by_type + type;

    assert(sv);
    assert(SvREFCNT(sv) == 0);

    if (type <= SVt_IV)
        return;

    if (SvOBJECT(sv)) {
        if (PL_defstash) {              /* Still have a symbol table? */
            dSP;
            HV* stash;
            do {        
                CV* destructor;
                stash = SvSTASH(sv);
                destructor = StashHANDLER(stash,DESTROY);
                if (destructor) {
                    SV* const tmpref = newRV(sv);
                    SvREADONLY_on(tmpref);   /* DESTROY() could be naughty */
                    ENTER;
                    PUSHSTACKi(PERLSI_DESTROY);
                    EXTEND(SP, 2);
                    PUSHMARK(SP);
                    PUSHs(tmpref);
                    PUTBACK;
                    call_sv((SV*)destructor, G_DISCARD|G_EVAL|G_KEEPERR|G_VOID);
                
                
                    POPSTACK;
                    SPAGAIN;
                    LEAVE;
                    if(SvREFCNT(tmpref) < 2) {
                        /* tmpref is not kept alive! */
                        SvREFCNT(sv)--;
                        SvRV_set(tmpref, NULL);
                        SvROK_off(tmpref);
                    }
                    SvREFCNT_dec(tmpref);
                }
            } while (SvOBJECT(sv) && SvSTASH(sv) != stash);


            if (SvREFCNT(sv)) {
                if (PL_in_clean_objs)
                    Perl_croak(aTHX_ "DESTROY created new reference to dead object '%s'",
                          HvNAME_get(stash));
                /* DESTROY gave object new lease on life */
                return;
            }
        }

        if (SvOBJECT(sv)) {
            SvREFCNT_dec(SvSTASH(sv));  /* possibly of changed persuasion */
            SvOBJECT_off(sv);   /* Curse the object. */
            if (type != SVt_PVIO)
                --PL_sv_objcount;       /* XXX Might want something more general */
        }
    }
    if (type >= SVt_PVMG) {
        if (SvMAGIC(sv))
            mg_free(sv);
        if (type == SVt_PVMG && SvFLAGS(sv) & SVpad_TYPED)
            SvREFCNT_dec(SvSTASH(sv));
    }
    switch (type) {
    case SVt_PVIO:
        if (IoIFP(sv) &&
            IoIFP(sv) != PerlIO_stdin() &&
            IoIFP(sv) != PerlIO_stdout() &&
            IoIFP(sv) != PerlIO_stderr())
        {
            io_close((IO*)sv, FALSE);
        }
        if (IoDIRP(sv) && !(IoFLAGS(sv) & IOf_FAKE_DIRP))
            PerlDir_close(IoDIRP(sv));
        IoDIRP(sv) = (DIR*)NULL;
        Safefree(IoTOP_NAME(sv));
        Safefree(IoFMT_NAME(sv));
        Safefree(IoBOTTOM_NAME(sv));
        goto freescalar;
    case SVt_PVBM:
        goto freescalar;
    case SVt_PVCV:
    case SVt_PVFM:
        cv_undef((CV*)sv);
        goto freescalar;
    case SVt_PVHV:
        Perl_hv_kill_backrefs(aTHX_ (HV*)sv);
        hv_undef((HV*)sv);
        break;
    case SVt_PVAV:
        av_undef((AV*)sv);
        break;
    case SVt_PVLV:
        if (LvTYPE(sv) == 'T') { /* for tie: return HE to pool */
            SvREFCNT_dec(HeKEY_sv((HE*)LvTARG(sv)));
            HeNEXT((HE*)LvTARG(sv)) = PL_hv_fetch_ent_mh;
            PL_hv_fetch_ent_mh = (HE*)LvTARG(sv);
        }
        else if (LvTYPE(sv) != 't') /* unless tie: unrefcnted fake SV**  */
            SvREFCNT_dec(LvTARG(sv));
        goto freescalar;