[perl5.git] / sv.c

/*    sv.c
 *
 *    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
 *    2000, 2001, 2002, 2003, 2004, 2005, 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)
{
    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)
{
    SV* sv;

    if (PL_nice_chunk) {
	sv_add_arena(PL_nice_chunk, PL_nice_chunk_size, 0);
	PL_nice_chunk = Nullch;
        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)
{
    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)
{
    SV* 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)
{
    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)
{
    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)
{
    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)
{
    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)
{
    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 = Nullav;
	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)
{
    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
*/
#define free_arena(name)					\
    STMT_START {						\
	S_free_arena(aTHX_ (void**) PL_ ## name ## _arenaroot);	\
	PL_ ## name ## _arenaroot = 0;				\
	PL_ ## name ## _root = 0;				\
    } STMT_END

void
Perl_sv_free_arenas(pTHX)
{
    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);
    }

    for (i=0; i<SVt_LAST; i++) {
	S_free_arena(aTHX_ (void**) PL_body_arenaroots[i]);
	PL_body_arenaroots[i] = 0;
	PL_body_roots[i] = 0;
    }

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

/* ---------------------------------------------------------------------
 *
 * support functions for report_uninit()
 */

/* the maxiumum size of array or hash where we will scan looking
 * for the undefined element that triggered the warning */

#define FUV_MAX_SEARCH_SIZE 1000

/* Look for an entry in the hash whose value has the same SV as val;
 * If so, return a mortal copy of the key. */

STATIC SV*
S_find_hash_subscript(pTHX_ HV *hv, SV* val)
{
    dVAR;
    register HE **array;
    I32 i;

    if (!hv || SvMAGICAL(hv) || !HvARRAY(hv) ||
			(HvTOTALKEYS(hv) > FUV_MAX_SEARCH_SIZE))
	return Nullsv;

    array = HvARRAY(hv);

    for (i=HvMAX(hv); i>0; i--) {
	register HE *entry;
	for (entry = array[i]; entry; entry = HeNEXT(entry)) {
	    if (HeVAL(entry) != val)
		continue;
	    if (    HeVAL(entry) == &PL_sv_undef ||
		    HeVAL(entry) == &PL_sv_placeholder)
		continue;
	    if (!HeKEY(entry))
		return Nullsv;
	    if (HeKLEN(entry) == HEf_SVKEY)
		return sv_mortalcopy(HeKEY_sv(entry));
	    return sv_2mortal(newSVpvn(HeKEY(entry), HeKLEN(entry)));
	}
    }
    return Nullsv;
}

/* Look for an entry in the array whose value has the same SV as val;
 * If so, return the index, otherwise return -1. */

STATIC I32
S_find_array_subscript(pTHX_ AV *av, SV* val)
{
    SV** svp;
    I32 i;
    if (!av || SvMAGICAL(av) || !AvARRAY(av) ||
			(AvFILLp(av) > FUV_MAX_SEARCH_SIZE))
	return -1;

    svp = AvARRAY(av);
    for (i=AvFILLp(av); i>=0; i--) {
	if (svp[i] == val && svp[i] != &PL_sv_undef)
	    return i;
    }
    return -1;
}

/* S_varname(): return the name of a variable, optionally with a subscript.
 * If gv is non-zero, use the name of that global, along with gvtype (one
 * of "$", "@", "%"); otherwise use the name of the lexical at pad offset
 * targ.  Depending on the value of the subscript_type flag, return:
 */

#define FUV_SUBSCRIPT_NONE	1	/* "@foo"          */
#define FUV_SUBSCRIPT_ARRAY	2	/* "$foo[aindex]"  */
#define FUV_SUBSCRIPT_HASH	3	/* "$foo{keyname}" */
#define FUV_SUBSCRIPT_WITHIN	4	/* "within @foo"   */

STATIC SV*
S_varname(pTHX_ GV *gv, const char gvtype, PADOFFSET targ,
	SV* keyname, I32 aindex, int subscript_type)
{

    SV * const name = sv_newmortal();
    if (gv) {
	char buffer[2];
	buffer[0] = gvtype;
	buffer[1] = 0;

	/* as gv_fullname4(), but add literal '^' for $^FOO names  */

	gv_fullname4(name, gv, buffer, 0);

	if ((unsigned int)SvPVX(name)[1] <= 26) {
	    buffer[0] = '^';
	    buffer[1] = SvPVX(name)[1] + 'A' - 1;

	    /* Swap the 1 unprintable control character for the 2 byte pretty
	       version - ie substr($name, 1, 1) = $buffer; */
	    sv_insert(name, 1, 1, buffer, 2);
	}
    }
    else {
	U32 unused;
	CV * const cv = find_runcv(&unused);
	SV *sv;
	AV *av;

	if (!cv || !CvPADLIST(cv))
	    return Nullsv;
	av = (AV*)(*av_fetch(CvPADLIST(cv), 0, FALSE));
	sv = *av_fetch(av, targ, FALSE);
	/* SvLEN in a pad name is not to be trusted */
	sv_setpv(name, SvPV_nolen_const(sv));
    }

    if (subscript_type == FUV_SUBSCRIPT_HASH) {
	SV * const sv = NEWSV(0,0);
	*SvPVX(name) = '$';
	Perl_sv_catpvf(aTHX_ name, "{%s}",
	    pv_display(sv,SvPVX_const(keyname), SvCUR(keyname), 0, 32));
	SvREFCNT_dec(sv);
    }
    else if (subscript_type == FUV_SUBSCRIPT_ARRAY) {
	*SvPVX(name) = '$';
	Perl_sv_catpvf(aTHX_ name, "[%"IVdf"]", (IV)aindex);
    }
    else if (subscript_type == FUV_SUBSCRIPT_WITHIN)
	sv_insert(name, 0, 0,  "within ", 7);

    return name;
}


/*
=for apidoc find_uninit_var

Find the name of the undefined variable (if any) that caused the operator o
to issue a "Use of uninitialized value" warning.
If match is true, only return a name if it's value matches uninit_sv.
So roughly speaking, if a unary operator (such as OP_COS) generates a
warning, then following the direct child of the op may yield an
OP_PADSV or OP_GV that gives the name of the undefined variable. On the
other hand, with OP_ADD there are two branches to follow, so we only print
the variable name if we get an exact match.

The name is returned as a mortal SV.

Assumes that PL_op is the op that originally triggered the error, and that
PL_comppad/PL_curpad points to the currently executing pad.

=cut
*/

STATIC SV *
S_find_uninit_var(pTHX_ OP* obase, SV* uninit_sv, bool match)
{
    dVAR;
    SV *sv;
    AV *av;
    GV *gv;
    OP *o, *o2, *kid;

    if (!obase || (match && (!uninit_sv || uninit_sv == &PL_sv_undef ||
			    uninit_sv == &PL_sv_placeholder)))
	return Nullsv;

    switch (obase->op_type) {

    case OP_RV2AV:
    case OP_RV2HV:
    case OP_PADAV:
    case OP_PADHV:
      {
	const bool pad  = (obase->op_type == OP_PADAV || obase->op_type == OP_PADHV);
	const bool hash = (obase->op_type == OP_PADHV || obase->op_type == OP_RV2HV);
	I32 index = 0;
	SV *keysv = Nullsv;
	int subscript_type = FUV_SUBSCRIPT_WITHIN;

	if (pad) { /* @lex, %lex */
	    sv = PAD_SVl(obase->op_targ);
	    gv = Nullgv;
	}
	else {
	    if (cUNOPx(obase)->op_first->op_type == OP_GV) {
	    /* @global, %global */
		gv = cGVOPx_gv(cUNOPx(obase)->op_first);
		if (!gv)
		    break;
		sv = hash ? (SV*)GvHV(gv): (SV*)GvAV(gv);
	    }
	    else /* @{expr}, %{expr} */
		return find_uninit_var(cUNOPx(obase)->op_first,
						    uninit_sv, match);
	}

	/* attempt to find a match within the aggregate */
	if (hash) {
	    keysv = S_find_hash_subscript(aTHX_ (HV*)sv, uninit_sv);
	    if (keysv)
		subscript_type = FUV_SUBSCRIPT_HASH;
	}
	else {
	    index = S_find_array_subscript(aTHX_ (AV*)sv, uninit_sv);
	    if (index >= 0)
		subscript_type = FUV_SUBSCRIPT_ARRAY;
	}

	if (match && subscript_type == FUV_SUBSCRIPT_WITHIN)
	    break;

	return varname(gv, hash ? '%' : '@', obase->op_targ,
				    keysv, index, subscript_type);
      }

    case OP_PADSV:
	if (match && PAD_SVl(obase->op_targ) != uninit_sv)
	    break;
	return varname(Nullgv, '$', obase->op_targ,
				    Nullsv, 0, FUV_SUBSCRIPT_NONE);

    case OP_GVSV:
	gv = cGVOPx_gv(obase);
	if (!gv || (match && GvSV(gv) != uninit_sv))
	    break;
	return varname(gv, '$', 0, Nullsv, 0, FUV_SUBSCRIPT_NONE);

    case OP_AELEMFAST:
	if (obase->op_flags & OPf_SPECIAL) { /* lexical array */
	    if (match) {
		SV **svp;
		av = (AV*)PAD_SV(obase->op_targ);
		if (!av || SvRMAGICAL(av))
		    break;
		svp = av_fetch(av, (I32)obase->op_private, FALSE);
		if (!svp || *svp != uninit_sv)
		    break;
	    }
	    return varname(Nullgv, '$', obase->op_targ,
		    Nullsv, (I32)obase->op_private, FUV_SUBSCRIPT_ARRAY);
	}
	else {
	    gv = cGVOPx_gv(obase);
	    if (!gv)
		break;
	    if (match) {
		SV **svp;
		av = GvAV(gv);
		if (!av || SvRMAGICAL(av))
		    break;
		svp = av_fetch(av, (I32)obase->op_private, FALSE);
		if (!svp || *svp != uninit_sv)
		    break;
	    }
	    return varname(gv, '$', 0,
		    Nullsv, (I32)obase->op_private, FUV_SUBSCRIPT_ARRAY);
	}
	break;

    case OP_EXISTS:
	o = cUNOPx(obase)->op_first;
	if (!o || o->op_type != OP_NULL ||
		! (o->op_targ == OP_AELEM || o->op_targ == OP_HELEM))
	    break;
	return find_uninit_var(cBINOPo->op_last, uninit_sv, match);

    case OP_AELEM:
    case OP_HELEM:
	if (PL_op == obase)
	    /* $a[uninit_expr] or $h{uninit_expr} */
	    return find_uninit_var(cBINOPx(obase)->op_last, uninit_sv, match);

	gv = Nullgv;
	o = cBINOPx(obase)->op_first;
	kid = cBINOPx(obase)->op_last;

	/* get the av or hv, and optionally the gv */
	sv = Nullsv;
	if  (o->op_type == OP_PADAV || o->op_type == OP_PADHV) {
	    sv = PAD_SV(o->op_targ);
	}
	else if ((o->op_type == OP_RV2AV || o->op_type == OP_RV2HV)
		&& cUNOPo->op_first->op_type == OP_GV)
	{
	    gv = cGVOPx_gv(cUNOPo->op_first);
	    if (!gv)
		break;
	    sv = o->op_type == OP_RV2HV ? (SV*)GvHV(gv) : (SV*)GvAV(gv);
	}
	if (!sv)
	    break;

	if (kid && kid->op_type == OP_CONST && SvOK(cSVOPx_sv(kid))) {
	    /* index is constant */
	    if (match) {
		if (SvMAGICAL(sv))
		    break;
		if (obase->op_type == OP_HELEM) {
		    HE* he = hv_fetch_ent((HV*)sv, cSVOPx_sv(kid), 0, 0);
		    if (!he || HeVAL(he) != uninit_sv)
			break;
		}
		else {
		    SV ** const svp = av_fetch((AV*)sv, SvIV(cSVOPx_sv(kid)), FALSE);
		    if (!svp || *svp != uninit_sv)
			break;
		}
	    }
	    if (obase->op_type == OP_HELEM)
		return varname(gv, '%', o->op_targ,
			    cSVOPx_sv(kid), 0, FUV_SUBSCRIPT_HASH);
	    else
		return varname(gv, '@', o->op_targ, Nullsv,
			    SvIV(cSVOPx_sv(kid)), FUV_SUBSCRIPT_ARRAY);
	    ;
	}
	else  {
	    /* index is an expression;
	     * attempt to find a match within the aggregate */
	    if (obase->op_type == OP_HELEM) {
		SV * const keysv = S_find_hash_subscript(aTHX_ (HV*)sv, uninit_sv);
		if (keysv)
		    return varname(gv, '%', o->op_targ,
						keysv, 0, FUV_SUBSCRIPT_HASH);
	    }
	    else {
		const I32 index = S_find_array_subscript(aTHX_ (AV*)sv, uninit_sv);
		if (index >= 0)
		    return varname(gv, '@', o->op_targ,
					Nullsv, index, FUV_SUBSCRIPT_ARRAY);
	    }
	    if (match)
		break;
	    return varname(gv,
		(o->op_type == OP_PADAV || o->op_type == OP_RV2AV)
		? '@' : '%',
		o->op_targ, Nullsv, 0, FUV_SUBSCRIPT_WITHIN);
	}

	break;

    case OP_AASSIGN:
	/* only examine RHS */
	return find_uninit_var(cBINOPx(obase)->op_first, uninit_sv, match);

    case OP_OPEN:
	o = cUNOPx(obase)->op_first;
	if (o->op_type == OP_PUSHMARK)
	    o = o->op_sibling;

	if (!o->op_sibling) {
	    /* one-arg version of open is highly magical */

	    if (o->op_type == OP_GV) { /* open FOO; */
		gv = cGVOPx_gv(o);
		if (match && GvSV(gv) != uninit_sv)
		    break;
		return varname(gv, '$', 0,
			    Nullsv, 0, FUV_SUBSCRIPT_NONE);
	    }
	    /* other possibilities not handled are:
	     * open $x; or open my $x;	should return '${*$x}'
	     * open expr;		should return '$'.expr ideally
	     */
	     break;
	}
	goto do_op;

    /* ops where $_ may be an implicit arg */
    case OP_TRANS:
    case OP_SUBST:
    case OP_MATCH:
	if ( !(obase->op_flags & OPf_STACKED)) {
	    if (uninit_sv == ((obase->op_private & OPpTARGET_MY)
				 ? PAD_SVl(obase->op_targ)
				 : DEFSV))
	    {
		sv = sv_newmortal();
		sv_setpvn(sv, "$_", 2);
		return sv;
	    }
	}
	goto do_op;

    case OP_PRTF:
    case OP_PRINT:
	/* skip filehandle as it can't produce 'undef' warning  */
	o = cUNOPx(obase)->op_first;
	if ((obase->op_flags & OPf_STACKED) && o->op_type == OP_PUSHMARK)
	    o = o->op_sibling->op_sibling;
	goto do_op2;


    case OP_RV2SV:
    case OP_CUSTOM:
    case OP_ENTERSUB:
	match = 1; /* XS or custom code could trigger random warnings */
	goto do_op;

    case OP_SCHOMP:
    case OP_CHOMP:
	if (SvROK(PL_rs) && uninit_sv == SvRV(PL_rs))
	    return sv_2mortal(newSVpvn("${$/}", 5));
	/* FALL THROUGH */

    default:
    do_op:
	if (!(obase->op_flags & OPf_KIDS))
	    break;
	o = cUNOPx(obase)->op_first;
	
    do_op2:
	if (!o)
	    break;

	/* if all except one arg are constant, or have no side-effects,
	 * or are optimized away, then it's unambiguous */
	o2 = Nullop;
	for (kid=o; kid; kid = kid->op_sibling) {
	    if (kid &&
		(    (kid->op_type == OP_CONST && SvOK(cSVOPx_sv(kid)))
		  || (kid->op_type == OP_NULL  && ! (kid->op_flags & OPf_KIDS))
		  || (kid->op_type == OP_PUSHMARK)
		)
	    )
		continue;
	    if (o2) { /* more than one found */
		o2 = Nullop;
		break;
	    }
	    o2 = kid;
	}
	if (o2)
	    return find_uninit_var(o2, uninit_sv, match);

	/* scan all args */
	while (o) {
	    sv = find_uninit_var(o, uninit_sv, 1);
	    if (sv)
		return sv;
	    o = o->op_sibling;
	}
	break;
    }
    return Nullsv;
}


/*
=for apidoc report_uninit

Print appropriate "Use of uninitialized variable" warning

=cut
*/

void
Perl_report_uninit(pTHX_ SV* uninit_sv)
{
    if (PL_op) {
	SV* varname = Nullsv;
	if (uninit_sv) {
	    varname = find_uninit_var(PL_op, uninit_sv,0);
	    if (varname)
		sv_insert(varname, 0, 0, " ", 1);
	}
	Perl_warner(aTHX_ packWARN(WARN_UNINITIALIZED), PL_warn_uninit,
		varname ? SvPV_nolen_const(varname) : "",
		" in ", OP_DESC(PL_op));
    }
    else
	Perl_warner(aTHX_ packWARN(WARN_UNINITIALIZED), PL_warn_uninit,
		    "", "", "");
}

/*
  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)
{
    void **arena_root	= &PL_body_arenaroots[sv_type];
    void **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) = *arena_root;
    *arena_root = (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 **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)
{
    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 **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)  */
    int 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

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),
     STRUCT_OFFSET(XPV, xpv_len) + sizeof (((XPV*)SvANY((SV*)0))->xpv_len)
     + STRUCT_OFFSET(xpv_allocated, xpv_cur) - STRUCT_OFFSET(XPV, xpv_cur),
     + STRUCT_OFFSET(xpv_allocated, xpv_cur) - STRUCT_OFFSET(XPV, xpv_cur)
     , FALSE, NONV, HASARENA},
    /* 12 */
    {sizeof(xpviv_allocated),
     STRUCT_OFFSET(XPVIV, xiv_u) + sizeof (((XPVIV*)SvANY((SV*)0))->xiv_u)
     + STRUCT_OFFSET(xpviv_allocated, xpv_cur) - STRUCT_OFFSET(XPVIV, xpv_cur),
     + STRUCT_OFFSET(xpviv_allocated, xpv_cur) - STRUCT_OFFSET(XPVIV, xpv_cur)
    , FALSE, NONV, HASARENA},
    /* 20 */
    {sizeof(XPVNV),
     STRUCT_OFFSET(XPVNV, xiv_u) + sizeof (((XPVNV*)SvANY((SV*)0))->xiv_u),
     0, FALSE, HADNV, HASARENA},
    /* 28 */
    {sizeof(XPVMG),
     STRUCT_OFFSET(XPVMG, xmg_stash) + sizeof (((XPVMG*)SvANY((SV*)0))->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),
     STRUCT_OFFSET(XPVAV, xmg_stash)
     + sizeof (((XPVAV*)SvANY((SV *)0))->xmg_stash)
     + STRUCT_OFFSET(xpvav_allocated, xav_fill)
     - STRUCT_OFFSET(XPVAV, xav_fill),
     STRUCT_OFFSET(xpvav_allocated, xav_fill)
     - STRUCT_OFFSET(XPVAV, xav_fill), TRUE, HADNV, HASARENA},
    /* 20 */
    {sizeof(xpvhv_allocated),
     STRUCT_OFFSET(XPVHV, xmg_stash)
     + sizeof (((XPVHV*)SvANY((SV *)0))->xmg_stash)
     + STRUCT_OFFSET(xpvhv_allocated, xhv_fill)
     - STRUCT_OFFSET(XPVHV, xhv_fill),
     STRUCT_OFFSET(xpvhv_allocated, xhv_fill)
     - STRUCT_OFFSET(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)
{
    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, (char*)0);

	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, 0);
	    SvSTASH_set(sv, 0);
	}
	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 store as all bits 0 then Zero() already creates a correct
       0.0 for us.  */
	if (old_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, 0);
	break;
    default:
	Perl_croak(aTHX_ "panic: sv_upgrade to unknown type %lu", 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)
{
    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)
{
    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)
{
     SV *dsv;
     char tmpbuf[64];
     const char *pv;

     if (DO_UTF8(sv)) {
          dsv = sv_2mortal(newSVpvn("", 0));
          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, *end;
	  for (s = SvPVX_const(sv), end = s + SvCUR(sv); 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)
{
    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*/

/*
=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)
{
    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))
	    return asIV(sv);
	if (!SvROK(sv)) {
	    if (!(SvFLAGS(sv) & SVs_PADTMP)) {
		if (!PL_localizing && ckWARN(WARN_UNINITIALIZED))
		    report_uninit(sv);
	    }
	    return 0;
	}
    }
    if (SvTHINKFIRST(sv)) {
	if (SvROK(sv)) {
	    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 (SvIsUV(sv)) {
	    return (IV)(SvUVX(sv));
	}
	else {
	    return SvIVX(sv);
	}
    }
    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.  NWC */

	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);
	  ret_iv_max:
	    DEBUG_c(PerlIO_printf(Perl_debug_log,
				  "0x%"UVxf" 2iv(%"UVuf" => %"IVdf") (as unsigned)\n",
				  PTR2UV(sv),
				  SvUVX(sv),
				  SvUVX(sv)));
	    return (IV)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 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, 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 NV preserves UV 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 {
		    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);
		    SvIsUV_on(sv);
		} else {
		    SvUV_set(sv, U_V(SvNVX(sv)));
		    /* 0xFFFFFFFFFFFFFFFF not an issue in here */
		    if ((NV)(SvUVX(sv)) == SvNVX(sv)) {
			SvIOK_on(sv);
			SvIsUV_on(sv);
		    } else {
			/* Integer is imprecise. NOK, IOKp, is UV */
			SvIsUV_on(sv);
		    }
		}
		goto ret_iv_max;
	    }
#else /* NV_PRESERVES_UV */
            if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
                == (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT)) {
                /* The IV 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.  */
                    if (sv_2iuv_non_preserve (sv, numtype)
                        >= IS_NUMBER_OVERFLOW_IV)
                    goto ret_iv_max;
                }
            }
#endif /* NV_PRESERVES_UV */
	}
    } else  {
	if (!PL_localizing && !(SvFLAGS(sv) & SVs_PADTMP) && 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;
    }
    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)
{
    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))
	    return asUV(sv);
	if (!SvROK(sv)) {
	    if (!(SvFLAGS(sv) & SVs_PADTMP)) {
		if (!PL_localizing && ckWARN(WARN_UNINITIALIZED))
		    report_uninit(sv);
	    }
	    return 0;
	}
    }
    if (SvTHINKFIRST(sv)) {
	if (SvROK(sv)) {
	  SV* tmpstr;
          if (SvAMAGIC(sv) && (tmpstr=AMG_CALLun(sv,numer)) &&
                (!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 (SvIsUV(sv)) {
	    return SvUVX(sv);
	}
	else {
	    return (UV)SvIVX(sv);
	}
    }
    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 */
	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" uv(%"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" uv(%"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" 2uv(%"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 a UV which
	   may be later translated to an NV, and the resulting NV is not
	   the translation of the initial data.
	
	   This means that if we cache such a UV, we need to cache the
	   NV as well.  Moreover, we trade speed for space, and do not
	   cache the NV if 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 NV preserves UV 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 it isn't 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);
		}
	    }
	}
	
	if ((numtype & (IS_NUMBER_IN_UV | IS_NUMBER_NOT_INT))
	    != IS_NUMBER_IN_UV) {
	    /* It wasn't an integer, or it overflowed 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" 2uv(%" PERL_PRIgldbl ")\n",
                                  PTR2UV(sv), SvNVX(sv)));
#else
            DEBUG_c(PerlIO_printf(Perl_debug_log, "0x%"UVxf" 2uv(%"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);
                    SvIsUV_on(sv);
                } 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);
                        SvIsUV_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 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_2uv 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
                    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;
    }

    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)
{
    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)) {
	    if (!(SvFLAGS(sv) & SVs_PADTMP)) {
		if (!PL_localizing && ckWARN(WARN_UNINITIALIZED))
		    report_uninit(sv);
	    }
            return (NV)0;
        }
    }
    if (SvTHINKFIRST(sv)) {
	if (SvROK(sv)) {
	  SV* tmpstr;
          if (SvAMAGIC(sv) && (tmpstr=AMG_CALLun(sv,numer)) &&
                (!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) {
	if (SvTYPE(sv) == SVt_IV)
	    sv_upgrade(sv, SVt_PVNV);
	else
	    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);
                            SvIOK_on(sv);
                        } else {
                            SvIOK_on(sv);
                            /* It had no "." so it must be integer.  */
                        }
                    } 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);
                            } else {
                                SvIOK_on(sv);
                            }
                        }
                    }
                }
            }
        }
#endif /* NV_PRESERVES_UV */
    }
    else  {
	if (!PL_localizing && !(SvFLAGS(sv) & SVs_PADTMP) && ckWARN(WARN_UNINITIALIZED))
	    report_uninit(sv);
	if (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.  */
	    sv_upgrade(sv, SVt_NV);
	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);
}

/* asIV(): extract an integer from the string value of an SV.
 * Caller must validate PVX  */

STATIC IV
S_asIV(pTHX_ SV *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)));
}

/* asUV(): extract an unsigned integer from the string value of an SV
 * Caller must validate PVX  */

STATIC UV
S_asUV(pTHX_ SV *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)));
}

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

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

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

/*
=for apidoc sv_2pv_flags

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

=cut
*/

char *
Perl_sv_2pv_flags(pTHX_ register SV *sv, STRLEN *lp, I32 flags)
{
    register char *s;
    int olderrno;
    SV *tsv, *origsv;
    char tbuf[64];	/* Must fit sprintf/Gconvert of longest IV/NV */
    char *tmpbuf = tbuf;
    STRLEN len = 0;	/* Hush gcc. len is always initialised before use.  */

    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)) {
	    len = SvIsUV(sv) ? my_sprintf(tmpbuf,"%"UVuf, (UV)SvUVX(sv))
		: my_sprintf(tmpbuf,"%"IVdf, (IV)SvIVX(sv));
	    tsv = Nullsv;
	    goto tokensave_has_len;
	}
	if (SvNOKp(sv)) {
	    Gconvert(SvNVX(sv), NV_DIG, 0, tmpbuf);
	    tsv = Nullsv;
	    goto tokensave;
	}
        if (!SvROK(sv)) {
	    if (!(SvFLAGS(sv) & SVs_PADTMP)) {
		if (!PL_localizing && ckWARN(WARN_UNINITIALIZED))
		    report_uninit(sv);
	    }
	    if (lp)
		*lp = 0;
            return (char *)"";
        }
    }
    if (SvTHINKFIRST(sv)) {
	if (SvROK(sv)) {
	    SV* tmpstr;
            register const char *typestr;
            if (SvAMAGIC(sv) && (tmpstr=AMG_CALLun(sv,string)) &&
                (!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;
            }
	    origsv = sv;
	    sv = (SV*)SvRV(sv);
	    if (!sv)
		typestr = "NULLREF";
	    else {
		MAGIC *mg;
		
		switch (SvTYPE(sv)) {
		case SVt_PVMG:
		    if ( ((SvFLAGS(sv) &
			   (SVs_OBJECT|SVf_OK|SVs_GMG|SVs_SMG|SVs_RMG))
			  == (SVs_OBJECT|SVs_SMG))
			 && (mg = mg_find(sv, PERL_MAGIC_qr))) {
                        const regexp *re = (regexp *)mg->mg_obj;

			if (!mg->mg_ptr) {
                            const char *fptr = "msix";
			    char reflags[6];
			    char ch;
			    int left = 0;
			    int right = 4;
                            char 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);
			    Copy("(?", mg->mg_ptr, 2, char);
			    Copy(reflags, mg->mg_ptr+2, left, char);
			    Copy(":", mg->mg_ptr+left+2, 1, char);
			    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(origsv);
			else
			    SvUTF8_off(origsv);
			if (lp)
			    *lp = mg->mg_len;
			return mg->mg_ptr;
		    }
					/* Fall through */
		case SVt_NULL:
		case SVt_IV:
		case SVt_NV:
		case SVt_RV:
		case SVt_PV:
		case SVt_PVIV:
		case SVt_PVNV:
		case SVt_PVBM:	typestr = SvROK(sv) ? "REF" : "SCALAR"; break;
		case SVt_PVLV:	typestr = SvROK(sv) ? "REF"
				/* tied lvalues should appear to be
				 * scalars for backwards compatitbility */
				: (LvTYPE(sv) == 't' || LvTYPE(sv) == 'T')
				    ? "SCALAR" : "LVALUE";	break;
		case SVt_PVAV:	typestr = "ARRAY";	break;
		case SVt_PVHV:	typestr = "HASH";	break;
		case SVt_PVCV:	typestr = "CODE";	break;
		case SVt_PVGV:	typestr = "GLOB";	break;
		case SVt_PVFM:	typestr = "FORMAT";	break;
		case SVt_PVIO:	typestr = "IO";		break;
		default:	typestr = "UNKNOWN";	break;
		}
		tsv = NEWSV(0,0);
		if (SvOBJECT(sv)) {
		    const char * const name = HvNAME_get(SvSTASH(sv));
		    Perl_sv_setpvf(aTHX_ tsv, "%s=%s(0x%"UVxf")",
				   name ? name : "__ANON__" , typestr, PTR2UV(sv));
		}
		else
		    Perl_sv_setpvf(aTHX_ tsv, "%s(0x%"UVxf")", typestr, PTR2UV(sv));
		goto tokensaveref;
	    }
	    if (lp)
		*lp = strlen(typestr);
	    return (char *)typestr;
	}
	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);
	if (isUIOK)
	    ptr = uiv_2buf(buf, 0, SvUVX(sv), 1, &ebuf);
	else
	    ptr = uiv_2buf(buf, SvIVX(sv), 0, 0, &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)) {
	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);
	olderrno = errno;	/* 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);

  tokensave:
    len = strlen(tmpbuf);
 tokensave_has_len:
    assert (!tsv);
    if (SvROK(sv)) {	/* XXX Skip this when sv_pvn_force calls */
	/* Sneaky stuff here */

      tokensaveref:
	if (!tsv)
	    tsv = newSVpvn(tmpbuf, len);
	sv_2mortal(tsv);
	if (lp)
	    *lp = SvCUR(tsv);
	return SvPVX(tsv);
    }
    else {
        dVAR;

#ifdef FIXNEGATIVEZERO
	if (len == 2 && tmpbuf[0] == '-' && tmpbuf[1] == '0') {
	    tmpbuf[0] = '0';
	    tmpbuf[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, tmpbuf, len + 1);
    }
}

/*
=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)
{
    SvGETMAGIC(sv);

    if (!SvOK(sv))
	return 0;
    if (SvROK(sv)) {
	SV* tmpsv;
        if (SvAMAGIC(sv) && (tmpsv=AMG_CALLun(sv,bool_)) &&
                (!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)
{
    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 *s = (U8 *) SvPVX_const(sv);
	const U8 * const e = (U8 *) SvEND(sv);
	const U8 *t = s;
	int hibit = 0;
	
	while (t < e) {
	    const U8 ch = *t++;
	    if ((hibit = !NATIVE_IS_INVARIANT(ch)))
		break;
	}
	if (hibit) {
	    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. */
	}
	/* 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)
{
    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
*/

void
Perl_sv_setsv_flags(pTHX_ SV *dstr, register SV *sstr, I32 flags)
{
    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);
	    if (SvTAINTED(sstr))
		SvTAINT(dstr);
	    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);
	    if (SvTAINTED(sstr))
		SvTAINT(dstr);
	    return;
	}
	goto undef_sstr;

    case SVt_RV: