Replace #6705 with a minimal doc patch.

[perl5.git] / ext / Storable / Storable.xs

/*
 * Store and retrieve mechanism.
 */

/*
 * $Id: Storable.xs,v 0.7.1.2 2000/08/14 07:19:27 ram Exp $
 *
 *  Copyright (c) 1995-2000, Raphael Manfredi
 *  
 *  You may redistribute only under the terms of the Artistic License,
 *  as specified in the README file that comes with the distribution.
 *
 * $Log: Storable.xs,v $
 * Revision 0.7.1.2  2000/08/14 07:19:27  ram
 * patch2: added a refcnt dec in retrieve_tied_key()
 *
 * Revision 0.7.1.1  2000/08/13 20:10:06  ram
 * patch1: was wrongly optimizing for "undef" values in hashes
 * patch1: added support for ref to tied items in hash/array
 * patch1: added overloading support
 *
 * Revision 0.7  2000/08/03 22:04:44  ram
 * Baseline for second beta release.
 *
 */

#include <EXTERN.h>
#include <perl.h>
#include <patchlevel.h>		/* Perl's one, needed since 5.6 */
#include <XSUB.h>

/*#define DEBUGME /* Debug mode, turns assertions on as well */
/*#define DASSERT /* Assertion mode */

/*
 * Pre PerlIO time when none of USE_PERLIO and PERLIO_IS_STDIO is defined
 * Provide them with the necessary defines so they can build with pre-5.004.
 */
#ifndef USE_PERLIO
#ifndef PERLIO_IS_STDIO
#define PerlIO FILE
#define PerlIO_getc(x) getc(x)
#define PerlIO_putc(f,x) putc(x,f)
#define PerlIO_read(x,y,z) fread(y,1,z,x)
#define PerlIO_write(x,y,z) fwrite(y,1,z,x)
#define PerlIO_stdoutf printf
#endif	/* PERLIO_IS_STDIO */
#endif	/* USE_PERLIO */

/*
 * Earlier versions of perl might be used, we can't assume they have the latest!
 */
#ifndef newRV_noinc
#define newRV_noinc(sv)		((Sv = newRV(sv)), --SvREFCNT(SvRV(Sv)), Sv)
#endif
#if (PATCHLEVEL <= 4)		/* Older perls (<= 5.004) lack PL_ namespace */
#define PL_sv_yes	sv_yes
#define PL_sv_no	sv_no
#define PL_sv_undef	sv_undef
#endif
#ifndef HvSHAREKEYS_off
#define HvSHAREKEYS_off(hv)	/* Ignore */
#endif

#ifdef DEBUGME
#ifndef DASSERT
#define DASSERT
#endif
#define TRACEME(x)	do { PerlIO_stdoutf x; PerlIO_stdoutf("\n"); } while (0)
#else
#define TRACEME(x)
#endif

#ifdef DASSERT
#define ASSERT(x,y)	do {									\
	if (!(x)) {												\
		PerlIO_stdoutf("ASSERT FAILED (\"%s\", line %d): ",	\
			__FILE__, __LINE__);							\
		PerlIO_stdoutf y; PerlIO_stdoutf("\n");				\
	}														\
} while (0)
#else
#define ASSERT(x,y)
#endif

/*
 * Type markers.
 */

#define C(x) ((char) (x))	/* For markers with dynamic retrieval handling */

#define SX_OBJECT	C(0)	/* Already stored object */
#define SX_LSCALAR	C(1)	/* Scalar (string) forthcoming (length, data) */
#define SX_ARRAY	C(2)	/* Array forthcominng (size, item list) */
#define SX_HASH		C(3)	/* Hash forthcoming (size, key/value pair list) */
#define SX_REF		C(4)	/* Reference to object forthcoming */
#define SX_UNDEF	C(5)	/* Undefined scalar */
#define SX_INTEGER	C(6)	/* Integer forthcoming */
#define SX_DOUBLE	C(7)	/* Double forthcoming */
#define SX_BYTE		C(8)	/* (signed) byte forthcoming */
#define SX_NETINT	C(9)	/* Integer in network order forthcoming */
#define SX_SCALAR	C(10)	/* Scalar (small) forthcoming (length, data) */
#define SX_TIED_ARRAY  C(11)  /* Tied array forthcoming */
#define SX_TIED_HASH   C(12)  /* Tied hash forthcoming */
#define SX_TIED_SCALAR C(13)  /* Tied scalar forthcoming */
#define SX_SV_UNDEF	C(14)	/* Perl's immortal PL_sv_undef */
#define SX_SV_YES	C(15)	/* Perl's immortal PL_sv_yes */
#define SX_SV_NO	C(16)	/* Perl's immortal PL_sv_no */
#define SX_BLESS	C(17)	/* Object is blessed */
#define SX_IX_BLESS	C(18)	/* Object is blessed, classname given by index */
#define SX_HOOK		C(19)	/* Stored via hook, user-defined */
#define SX_OVERLOAD	C(20)	/* Overloaded reference */
#define SX_TIED_KEY C(21)   /* Tied magic key forthcoming */
#define SX_TIED_IDX C(22)   /* Tied magic index forthcoming */
#define SX_ERROR	C(23)	/* Error */

/*
 * Those are only used to retrieve "old" pre-0.6 binary images.
 */
#define SX_ITEM		'i'		/* An array item introducer */
#define SX_IT_UNDEF	'I'		/* Undefined array item */
#define SX_KEY		'k'		/* An hash key introducer */
#define SX_VALUE	'v'		/* An hash value introducer */
#define SX_VL_UNDEF	'V'		/* Undefined hash value */

/*
 * Those are only used to retrieve "old" pre-0.7 binary images
 */

#define SX_CLASS	'b'		/* Object is blessed, class name length <255 */
#define SX_LG_CLASS 'B'		/* Object is blessed, class name length >255 */
#define SX_STORED	'X'		/* End of object */

/*
 * Limits between short/long length representation.
 */

#define LG_SCALAR	255		/* Large scalar length limit */
#define LG_BLESS	127		/* Large classname bless limit */

/*
 * Operation types
 */

#define ST_STORE	0x1		/* Store operation */
#define ST_RETRIEVE	0x2		/* Retrieval operation */
#define ST_CLONE	0x4		/* Deep cloning operation */

/*
 * The following structure is used for hash table key retrieval. Since, when
 * retrieving objects, we'll be facing blessed hash references, it's best
 * to pre-allocate that buffer once and resize it as the need arises, never
 * freeing it (keys will be saved away someplace else anyway, so even large
 * keys are not enough a motivation to reclaim that space).
 *
 * This structure is also used for memory store/retrieve operations which
 * happen in a fixed place before being malloc'ed elsewhere if persistency
 * is required. Hence the aptr pointer.
 */
struct extendable {
	char *arena;		/* Will hold hash key strings, resized as needed */
	STRLEN asiz;		/* Size of aforementionned buffer */
	char *aptr;			/* Arena pointer, for in-place read/write ops */
	char *aend;			/* First invalid address */
};

/*
 * At store time:
 * An hash table records the objects which have already been stored.
 * Those are referred to as SX_OBJECT in the file, and their "tag" (i.e.
 * an arbitrary sequence number) is used to identify them.
 *
 * At retrieve time:
 * An array table records the objects which have already been retrieved,
 * as seen by the tag determind by counting the objects themselves. The
 * reference to that retrieved object is kept in the table, and is returned
 * when an SX_OBJECT is found bearing that same tag.
 *
 * The same processing is used to record "classname" for blessed objects:
 * indexing by a hash at store time, and via an array at retrieve time.
 */

typedef unsigned long stag_t;	/* Used by pre-0.6 binary format */

/*
 * The following "thread-safe" related defines were contributed by
 * Murray Nesbitt <murray@activestate.com> and integrated by RAM, who
 * only renamed things a little bit to ensure consistency with surrounding
 * code.	-- RAM, 14/09/1999
 *
 * The original patch suffered from the fact that the stcxt_t structure
 * was global.  Murray tried to minimize the impact on the code as much as
 * possible.
 *
 * Starting with 0.7, Storable can be re-entrant, via the STORABLE_xxx hooks
 * on objects.  Therefore, the notion of context needs to be generalized,
 * threading or not.
 */

#define MY_VERSION "Storable(" XS_VERSION ")"

typedef struct stcxt {
	int entry;			/* flags recursion */
	int optype;			/* type of traversal operation */
    HV *hseen;			/* which objects have been seen, store time */
    AV *aseen;			/* which objects have been seen, retrieve time */
    HV *hclass;			/* which classnames have been seen, store time */
    AV *aclass;			/* which classnames have been seen, retrieve time */
    HV *hook;			/* cache for hook methods per class name */
    I32 tagnum;			/* incremented at store time for each seen object */
    I32 classnum;		/* incremented at store time for each seen classname */
    int netorder;		/* true if network order used */
    int forgive_me;		/* whether to be forgiving... */
    int canonical;		/* whether to store hashes sorted by key */
	int dirty;			/* context is dirty due to CROAK() -- can be cleaned */
    struct extendable keybuf;	/* for hash key retrieval */
    struct extendable membuf;	/* for memory store/retrieve operations */
	PerlIO *fio;		/* where I/O are performed, NULL for memory */
	int ver_major;		/* major of version for retrieved object */
	int ver_minor;		/* minor of version for retrieved object */
	SV *(**retrieve_vtbl)();	/* retrieve dispatch table */
	struct stcxt *prev;	/* contexts chained backwards in real recursion */
} stcxt_t;

#if defined(MULTIPLICITY) || defined(PERL_OBJECT) || defined(PERL_CAPI)

#if (PATCHLEVEL <= 4) && (SUBVERSION < 68)
#define dSTCXT_SV 									\
	SV *perinterp_sv = perl_get_sv(MY_VERSION, FALSE)
#else	/* >= perl5.004_68 */
#define dSTCXT_SV									\
	SV *perinterp_sv = *hv_fetch(PL_modglobal,		\
		MY_VERSION, sizeof(MY_VERSION)-1, TRUE)
#endif	/* < perl5.004_68 */

#define dSTCXT_PTR(T,name)							\
	T name = (T)(perinterp_sv && SvIOK(perinterp_sv)\
				? SvIVX(perinterp_sv) : NULL)
#define dSTCXT										\
	dSTCXT_SV;										\
	dSTCXT_PTR(stcxt_t *, cxt)

#define INIT_STCXT									\
      dSTCXT;										\
      Newz(0, cxt, 1, stcxt_t);						\
      sv_setiv(perinterp_sv, (IV) cxt)

#define SET_STCXT(x) do {							\
	dSTCXT_SV;										\
	sv_setiv(perinterp_sv, (IV) (x));				\
} while (0)

#else /* !MULTIPLICITY && !PERL_OBJECT && !PERL_CAPI */

static stcxt_t Context;
static stcxt_t *Context_ptr = &Context;
#define dSTCXT			stcxt_t *cxt = Context_ptr
#define INIT_STCXT		dSTCXT
#define SET_STCXT(x)	Context_ptr = x

#endif /* MULTIPLICITY || PERL_OBJECT || PERL_CAPI */

/*
 * KNOWN BUG:
 *   Croaking implies a memory leak, since we don't use setjmp/longjmp
 *   to catch the exit and free memory used during store or retrieve
 *   operations.  This is not too difficult to fix, but I need to understand
 *   how Perl does it, and croaking is exceptional anyway, so I lack the
 *   motivation to do it.
 *
 * The current workaround is to mark the context as dirty when croaking,
 * so that data structures can be freed whenever we renter Storable code
 * (but only *then*: it's a workaround, not a fix).
 *
 * This is also imperfect, because we don't really know how far they trapped
 * the croak(), and when we were recursing, we won't be able to clean anything
 * but the topmost context stacked.
 */

#define CROAK(x)	do { cxt->dirty = 1; croak x; } while (0)

/*
 * End of "thread-safe" related definitions.
 */

/*
 * key buffer handling
 */
#define kbuf	(cxt->keybuf).arena
#define ksiz	(cxt->keybuf).asiz
#define KBUFINIT() do {					\
	if (!kbuf) {						\
		TRACEME(("** allocating kbuf of 128 bytes")); \
		New(10003, kbuf, 128, char);	\
		ksiz = 128;						\
	}									\
} while (0)
#define KBUFCHK(x) do {			\
	if (x >= ksiz) {			\
		TRACEME(("** extending kbuf to %d bytes", x+1)); \
		Renew(kbuf, x+1, char);	\
		ksiz = x+1;				\
	}							\
} while (0)

/*
 * memory buffer handling
 */
#define mbase	(cxt->membuf).arena
#define msiz	(cxt->membuf).asiz
#define mptr	(cxt->membuf).aptr
#define mend	(cxt->membuf).aend

#define MGROW	(1 << 13)
#define MMASK	(MGROW - 1)

#define round_mgrow(x)	\
	((unsigned long) (((unsigned long) (x) + MMASK) & ~MMASK))
#define trunc_int(x)	\
	((unsigned long) ((unsigned long) (x) & ~(sizeof(int)-1)))
#define int_aligned(x)	\
	((unsigned long) (x) == trunc_int(x))

#define MBUF_INIT(x) do {				\
	if (!mbase) {						\
		TRACEME(("** allocating mbase of %d bytes", MGROW)); \
		New(10003, mbase, MGROW, char);	\
		msiz = MGROW;					\
	}									\
	mptr = mbase;						\
	if (x)								\
		mend = mbase + x;				\
	else								\
		mend = mbase + msiz;			\
} while (0)

#define MBUF_TRUNC(x)	mptr = mbase + x
#define MBUF_SIZE()		(mptr - mbase)

/*
 * Use SvPOKp(), because SvPOK() fails on tainted scalars.
 * See store_scalar() for other usage of this workaround.
 */
#define MBUF_LOAD(v) do {				\
	if (!SvPOKp(v))						\
		CROAK(("Not a scalar string"));	\
	mptr = mbase = SvPV(v, msiz);		\
	mend = mbase + msiz;				\
} while (0)

#define MBUF_XTEND(x) do {			\
	int nsz = (int) round_mgrow((x)+msiz);	\
	int offset = mptr - mbase;		\
	TRACEME(("** extending mbase to %d bytes", nsz));	\
	Renew(mbase, nsz, char);		\
	msiz = nsz;						\
	mptr = mbase + offset;			\
	mend = mbase + nsz;				\
} while (0)

#define MBUF_CHK(x) do {			\
	if ((mptr + (x)) > mend)		\
		MBUF_XTEND(x);				\
} while (0)

#define MBUF_GETC(x) do {			\
	if (mptr < mend)				\
		x = (int) (unsigned char) *mptr++;	\
	else							\
		return (SV *) 0;			\
} while (0)

#define MBUF_GETINT(x) do {				\
	if ((mptr + sizeof(int)) <= mend) {	\
		if (int_aligned(mptr))			\
			x = *(int *) mptr;			\
		else							\
			memcpy(&x, mptr, sizeof(int));	\
		mptr += sizeof(int);			\
	} else								\
		return (SV *) 0;				\
} while (0)

#define MBUF_READ(x,s) do {			\
	if ((mptr + (s)) <= mend) {		\
		memcpy(x, mptr, s);			\
		mptr += s;					\
	} else							\
		return (SV *) 0;			\
} while (0)

#define MBUF_SAFEREAD(x,s,z) do {	\
	if ((mptr + (s)) <= mend) {		\
		memcpy(x, mptr, s);			\
		mptr += s;					\
	} else {						\
		sv_free(z);					\
		return (SV *) 0;			\
	}								\
} while (0)

#define MBUF_PUTC(c) do {			\
	if (mptr < mend)				\
		*mptr++ = (char) c;			\
	else {							\
		MBUF_XTEND(1);				\
		*mptr++ = (char) c;			\
	}								\
} while (0)

#define MBUF_PUTINT(i) do {			\
	MBUF_CHK(sizeof(int));			\
	if (int_aligned(mptr))			\
		*(int *) mptr = i;			\
	else							\
		memcpy(mptr, &i, sizeof(int));	\
	mptr += sizeof(int);			\
} while (0)

#define MBUF_WRITE(x,s) do {		\
	MBUF_CHK(s);					\
	memcpy(mptr, x, s);				\
	mptr += s;						\
} while (0)

/*
 * LOW_32BITS
 *
 * Keep only the low 32 bits of a pointer (used for tags, which are not
 * really pointers).
 */

#if PTRSIZE <= 4
#define LOW_32BITS(x)	((I32) (x))
#else
#define LOW_32BITS(x)	((I32) ((unsigned long) (x) & 0xffffffffUL))
#endif

/*
 * Possible return values for sv_type().
 */

#define svis_REF		0
#define svis_SCALAR		1
#define svis_ARRAY		2
#define svis_HASH		3
#define svis_TIED		4
#define svis_TIED_ITEM	5
#define svis_OTHER		6

/*
 * Flags for SX_HOOK.
 */

#define SHF_TYPE_MASK		0x03
#define SHF_LARGE_CLASSLEN	0x04
#define SHF_LARGE_STRLEN	0x08
#define SHF_LARGE_LISTLEN	0x10
#define SHF_IDX_CLASSNAME	0x20
#define SHF_NEED_RECURSE	0x40
#define SHF_HAS_LIST		0x80

/*
 * Types for SX_HOOK (2 bits).
 */

#define SHT_SCALAR			0
#define SHT_ARRAY			1
#define SHT_HASH			2

/*
 * Before 0.6, the magic string was "perl-store" (binary version number 0).
 *
 * Since 0.6 introduced many binary incompatibilities, the magic string has
 * been changed to "pst0" to allow an old image to be properly retrieved by
 * a newer Storable, but ensure a newer image cannot be retrieved with an
 * older version.
 *
 * At 0.7, objects are given the ability to serialize themselves, and the
 * set of markers is extended, backward compatibility is not jeopardized,
 * so the binary version number could have remained unchanged.  To correctly
 * spot errors if a file making use of 0.7-specific extensions is given to
 * 0.6 for retrieval, the binary version was moved to "2".  And I'm introducing
 * a "minor" version, to better track this kind of evolution from now on.
 * 
 */
static char old_magicstr[] = "perl-store";	/* Magic number before 0.6 */
static char magicstr[] = "pst0";			/* Used as a magic number */

#define STORABLE_BIN_MAJOR	2				/* Binary major "version" */
#define STORABLE_BIN_MINOR	1				/* Binary minor "version" */

/*
 * Useful store shortcuts...
 */

#define PUTMARK(x) do {						\
	if (!cxt->fio)							\
		MBUF_PUTC(x);						\
	else if (PerlIO_putc(cxt->fio, x) == EOF)	\
		return -1;							\
} while (0)

#ifdef HAS_HTONL
#define WLEN(x)	do {				\
	if (cxt->netorder) {			\
		int y = (int) htonl(x);		\
		if (!cxt->fio)				\
			MBUF_PUTINT(y);			\
		else if (PerlIO_write(cxt->fio, &y, sizeof(y)) != sizeof(y))	\
			return -1;				\
	} else {						\
		if (!cxt->fio)				\
			MBUF_PUTINT(x);			\
		else if (PerlIO_write(cxt->fio, &x, sizeof(x)) != sizeof(x))	\
			return -1;				\
	}								\
} while (0)
#else
#define WLEN(x)	do {				\
	if (!cxt->fio)					\
		MBUF_PUTINT(x);				\
	else if (PerlIO_write(cxt->fio, &x, sizeof(x)) != sizeof(x))	\
		return -1;					\
	} while (0)
#endif

#define WRITE(x,y) do {						\
	if (!cxt->fio)							\
		MBUF_WRITE(x,y);					\
	else if (PerlIO_write(cxt->fio, x, y) != y)	\
		return -1;							\
	} while (0)

#define STORE_SCALAR(pv, len) do {		\
	if (len <= LG_SCALAR) {				\
		unsigned char clen = (unsigned char) len;	\
		PUTMARK(SX_SCALAR);				\
		PUTMARK(clen);					\
		if (len)						\
			WRITE(pv, len);				\
	} else {							\
		PUTMARK(SX_LSCALAR);			\
		WLEN(len);						\
		WRITE(pv, len);					\
	}									\
} while (0)

/*
 * Store undef in arrays and hashes without recursing through store().
 */
#define STORE_UNDEF() do {				\
	cxt->tagnum++;						\
	PUTMARK(SX_UNDEF);					\
} while (0)

/*
 * Useful retrieve shortcuts...
 */

#define GETCHAR() \
	(cxt->fio ? PerlIO_getc(cxt->fio) : (mptr >= mend ? EOF : (int) *mptr++))

#define GETMARK(x) do {							\
	if (!cxt->fio)								\
		MBUF_GETC(x);							\
	else if ((x = PerlIO_getc(cxt->fio)) == EOF)	\
		return (SV *) 0;						\
} while (0)

#ifdef HAS_NTOHL
#define RLEN(x)	do {					\
	if (!cxt->fio)						\
		MBUF_GETINT(x);					\
	else if (PerlIO_read(cxt->fio, &x, sizeof(x)) != sizeof(x))	\
		return (SV *) 0;				\
	if (cxt->netorder)					\
		x = (int) ntohl(x);				\
} while (0)
#else
#define RLEN(x)	do {					\
	if (!cxt->fio)						\
		MBUF_GETINT(x);					\
	else if (PerlIO_read(cxt->fio, &x, sizeof(x)) != sizeof(x))	\
		return (SV *) 0;				\
} while (0)
#endif

#define READ(x,y) do {						\
	if (!cxt->fio)							\
		MBUF_READ(x, y);					\
	else if (PerlIO_read(cxt->fio, x, y) != y)	\
		return (SV *) 0;					\
} while (0)

#define SAFEREAD(x,y,z) do { 					\
	if (!cxt->fio)								\
		MBUF_SAFEREAD(x,y,z);					\
	else if (PerlIO_read(cxt->fio, x, y) != y)	 {	\
		sv_free(z);								\
		return (SV *) 0;						\
	}											\
} while (0)

/*
 * This macro is used at retrieve time, to remember where object 'y', bearing a
 * given tag 'tagnum', has been retrieved. Next time we see an SX_OBJECT marker,
 * we'll therefore know where it has been retrieved and will be able to
 * share the same reference, as in the original stored memory image.
 */
#define SEEN(y) do {						\
	if (!y)									\
		return (SV *) 0;					\
	if (av_store(cxt->aseen, cxt->tagnum++, SvREFCNT_inc(y)) == 0) \
		return (SV *) 0;					\
	TRACEME(("aseen(#%d) = 0x%lx (refcnt=%d)", cxt->tagnum-1, \
		(unsigned long) y, SvREFCNT(y)-1)); \
} while (0)

/*
 * Bless `s' in `p', via a temporary reference, required by sv_bless().
 */
#define BLESS(s,p) do {					\
	SV *ref;								\
	HV *stash;								\
	TRACEME(("blessing 0x%lx in %s", (unsigned long) (s), (p))); \
	stash = gv_stashpv((p), TRUE);			\
	ref = newRV_noinc(s);					\
	(void) sv_bless(ref, stash);			\
	SvRV(ref) = 0;							\
	SvREFCNT_dec(ref);						\
} while (0)

static int store();
static SV *retrieve();

/*
 * Dynamic dispatching table for SV store.
 */

static int store_ref(stcxt_t *cxt, SV *sv);
static int store_scalar(stcxt_t *cxt, SV *sv);
static int store_array(stcxt_t *cxt, AV *av);
static int store_hash(stcxt_t *cxt, HV *hv);
static int store_tied(stcxt_t *cxt, SV *sv);
static int store_tied_item(stcxt_t *cxt, SV *sv);
static int store_other(stcxt_t *cxt, SV *sv);

static int (*sv_store[])() = {
	store_ref,			/* svis_REF */
	store_scalar,		/* svis_SCALAR */
	store_array,		/* svis_ARRAY */
	store_hash,			/* svis_HASH */
	store_tied,			/* svis_TIED */
	store_tied_item,	/* svis_TIED_ITEM */
	store_other,		/* svis_OTHER */
};

#define SV_STORE(x)	(*sv_store[x])

/*
 * Dynamic dispatching tables for SV retrieval.
 */

static SV *retrieve_lscalar(stcxt_t *cxt);
static SV *old_retrieve_array(stcxt_t *cxt);
static SV *old_retrieve_hash(stcxt_t *cxt);
static SV *retrieve_ref(stcxt_t *cxt);
static SV *retrieve_undef(stcxt_t *cxt);
static SV *retrieve_integer(stcxt_t *cxt);
static SV *retrieve_double(stcxt_t *cxt);
static SV *retrieve_byte(stcxt_t *cxt);
static SV *retrieve_netint(stcxt_t *cxt);
static SV *retrieve_scalar(stcxt_t *cxt);
static SV *retrieve_tied_array(stcxt_t *cxt);
static SV *retrieve_tied_hash(stcxt_t *cxt);
static SV *retrieve_tied_scalar(stcxt_t *cxt);
static SV *retrieve_other(stcxt_t *cxt);

static SV *(*sv_old_retrieve[])() = {
	0,			/* SX_OBJECT -- entry unused dynamically */
	retrieve_lscalar,		/* SX_LSCALAR */
	old_retrieve_array,		/* SX_ARRAY -- for pre-0.6 binaries */
	old_retrieve_hash,		/* SX_HASH -- for pre-0.6 binaries */
	retrieve_ref,			/* SX_REF */
	retrieve_undef,			/* SX_UNDEF */
	retrieve_integer,		/* SX_INTEGER */
	retrieve_double,		/* SX_DOUBLE */
	retrieve_byte,			/* SX_BYTE */
	retrieve_netint,		/* SX_NETINT */
	retrieve_scalar,		/* SX_SCALAR */
	retrieve_tied_array,	/* SX_ARRAY */
	retrieve_tied_hash,		/* SX_HASH */
	retrieve_tied_scalar,	/* SX_SCALAR */
	retrieve_other,			/* SX_SV_UNDEF not supported */
	retrieve_other,			/* SX_SV_YES not supported */
	retrieve_other,			/* SX_SV_NO not supported */
	retrieve_other,			/* SX_BLESS not supported */
	retrieve_other,			/* SX_IX_BLESS not supported */
	retrieve_other,			/* SX_HOOK not supported */
	retrieve_other,			/* SX_OVERLOADED not supported */
	retrieve_other,			/* SX_TIED_KEY not supported */
	retrieve_other,			/* SX_TIED_IDX not supported */
	retrieve_other,			/* SX_ERROR */
};

static SV *retrieve_array(stcxt_t *cxt);
static SV *retrieve_hash(stcxt_t *cxt);
static SV *retrieve_sv_undef(stcxt_t *cxt);
static SV *retrieve_sv_yes(stcxt_t *cxt);
static SV *retrieve_sv_no(stcxt_t *cxt);
static SV *retrieve_blessed(stcxt_t *cxt);
static SV *retrieve_idx_blessed(stcxt_t *cxt);
static SV *retrieve_hook(stcxt_t *cxt);
static SV *retrieve_overloaded(stcxt_t *cxt);
static SV *retrieve_tied_key(stcxt_t *cxt);
static SV *retrieve_tied_idx(stcxt_t *cxt);

static SV *(*sv_retrieve[])() = {
	0,			/* SX_OBJECT -- entry unused dynamically */
	retrieve_lscalar,		/* SX_LSCALAR */
	retrieve_array,			/* SX_ARRAY */
	retrieve_hash,			/* SX_HASH */
	retrieve_ref,			/* SX_REF */
	retrieve_undef,			/* SX_UNDEF */
	retrieve_integer,		/* SX_INTEGER */
	retrieve_double,		/* SX_DOUBLE */
	retrieve_byte,			/* SX_BYTE */
	retrieve_netint,		/* SX_NETINT */
	retrieve_scalar,		/* SX_SCALAR */
	retrieve_tied_array,	/* SX_ARRAY */
	retrieve_tied_hash,		/* SX_HASH */
	retrieve_tied_scalar,	/* SX_SCALAR */
	retrieve_sv_undef,		/* SX_SV_UNDEF */
	retrieve_sv_yes,		/* SX_SV_YES */
	retrieve_sv_no,			/* SX_SV_NO */
	retrieve_blessed,		/* SX_BLESS */
	retrieve_idx_blessed,	/* SX_IX_BLESS */
	retrieve_hook,			/* SX_HOOK */
	retrieve_overloaded,	/* SX_OVERLOAD */
	retrieve_tied_key,		/* SX_TIED_KEY */
	retrieve_tied_idx,		/* SX_TIED_IDX */
	retrieve_other,			/* SX_ERROR */
};

#define RETRIEVE(c,x) (*(c)->retrieve_vtbl[(x) >= SX_ERROR ? SX_ERROR : (x)])

static SV *mbuf2sv();
static int store_blessed();

/***
 *** Context management.
 ***/

/*
 * init_perinterp
 *
 * Called once per "thread" (interpreter) to initialize some global context.
 */
static void init_perinterp() {
    INIT_STCXT;

    cxt->netorder = 0;		/* true if network order used */
    cxt->forgive_me = -1;	/* whether to be forgiving... */
}

/*
 * init_store_context
 *
 * Initialize a new store context for real recursion.
 */
static void init_store_context(cxt, f, optype, network_order)
stcxt_t *cxt;
PerlIO *f;
int optype;
int network_order;
{
	TRACEME(("init_store_context"));

	cxt->netorder = network_order;
	cxt->forgive_me = -1;			/* Fetched from perl if needed */
	cxt->canonical = -1;			/* Idem */
	cxt->tagnum = -1;				/* Reset tag numbers */
	cxt->classnum = -1;				/* Reset class numbers */
	cxt->fio = f;					/* Where I/O are performed */
	cxt->optype = optype;			/* A store, or a deep clone */
	cxt->entry = 1;					/* No recursion yet */

	/*
	 * The `hseen' table is used to keep track of each SV stored and their
	 * associated tag numbers is special. It is "abused" because the
	 * values stored are not real SV, just integers cast to (SV *),
	 * which explains the freeing below.
	 *
	 * It is also one possible bottlneck to achieve good storing speed,
	 * so the "shared keys" optimization is turned off (unlikely to be
	 * of any use here), and the hash table is "pre-extended". Together,
	 * those optimizations increase the throughput by 12%.
	 */

	cxt->hseen = newHV();			/* Table where seen objects are stored */
	HvSHAREKEYS_off(cxt->hseen);

	/*
	 * The following does not work well with perl5.004_04, and causes
	 * a core dump later on, in a completely unrelated spot, which
	 * makes me think there is a memory corruption going on.
	 *
	 * Calling hv_ksplit(hseen, HBUCKETS) instead of manually hacking
	 * it below does not make any difference. It seems to work fine
	 * with perl5.004_68 but given the probable nature of the bug,
	 * that does not prove anything.
	 *
	 * It's a shame because increasing the amount of buckets raises
	 * store() throughput by 5%, but until I figure this out, I can't
	 * allow for this to go into production.
	 *
	 * It is reported fixed in 5.005, hence the #if.
	 */
#if PATCHLEVEL < 5
#define HBUCKETS	4096				/* Buckets for %hseen */
	HvMAX(cxt->hseen) = HBUCKETS - 1;	/* keys %hseen = $HBUCKETS; */
#endif

	/*
	 * The `hclass' hash uses the same settings as `hseen' above, but it is
	 * used to assign sequential tags (numbers) to class names for blessed
	 * objects.
	 *
	 * We turn the shared key optimization on.
	 */

	cxt->hclass = newHV();			/* Where seen classnames are stored */

#if PATCHLEVEL < 5
	HvMAX(cxt->hclass) = HBUCKETS - 1;	/* keys %hclass = $HBUCKETS; */
#endif

	/*
	 * The `hook' hash table is used to keep track of the references on
	 * the STORABLE_freeze hook routines, when found in some class name.
	 *
	 * It is assumed that the inheritance tree will not be changed during
	 * storing, and that no new method will be dynamically created by the
	 * hooks.
	 */

	cxt->hook = newHV();			/* Table where hooks are cached */
}

/*
 * clean_store_context
 *
 * Clean store context by
 */
static void clean_store_context(cxt)
stcxt_t *cxt;
{
	HE *he;

	TRACEME(("clean_store_context"));

	ASSERT(cxt->optype & ST_STORE, ("was performing a store()"));

	/*
	 * Insert real values into hashes where we stored faked pointers.
	 */

	hv_iterinit(cxt->hseen);
	while (he = hv_iternext(cxt->hseen))
		HeVAL(he) = &PL_sv_undef;

	hv_iterinit(cxt->hclass);
	while (he = hv_iternext(cxt->hclass))
		HeVAL(he) = &PL_sv_undef;

	/*
	 * And now dispose of them...
	 */

	hv_undef(cxt->hseen);
	sv_free((SV *) cxt->hseen);

	hv_undef(cxt->hclass);
	sv_free((SV *) cxt->hclass);

	hv_undef(cxt->hook);
	sv_free((SV *) cxt->hook);

	cxt->entry = 0;
	cxt->dirty = 0;
}

/*
 * init_retrieve_context
 *
 * Initialize a new retrieve context for real recursion.
 */
static void init_retrieve_context(cxt, optype)
stcxt_t *cxt;
int optype;
{
	TRACEME(("init_retrieve_context"));

	/*
	 * The hook hash table is used to keep track of the references on
	 * the STORABLE_thaw hook routines, when found in some class name.
	 *
	 * It is assumed that the inheritance tree will not be changed during
	 * storing, and that no new method will be dynamically created by the
	 * hooks.
	 */

	cxt->hook  = newHV();			/* Caches STORABLE_thaw */

	/*
	 * If retrieving an old binary version, the cxt->retrieve_vtbl variable
	 * was set to sv_old_retrieve. We'll need a hash table to keep track of
	 * the correspondance between the tags and the tag number used by the
	 * new retrieve routines.
	 */

	cxt->hseen = (cxt->retrieve_vtbl == sv_old_retrieve) ? newHV() : 0;

	cxt->aseen = newAV();			/* Where retrieved objects are kept */
	cxt->aclass = newAV();			/* Where seen classnames are kept */
	cxt->tagnum = 0;				/* Have to count objects... */
	cxt->classnum = 0;				/* ...and class names as well */
	cxt->optype = optype;
	cxt->entry = 1;					/* No recursion yet */
}

/*
 * clean_retrieve_context
 *
 * Clean retrieve context by
 */
static void clean_retrieve_context(cxt)
stcxt_t *cxt;
{
	TRACEME(("clean_retrieve_context"));

	ASSERT(cxt->optype & ST_RETRIEVE, ("was performing a retrieve()"));

	av_undef(cxt->aseen);
	sv_free((SV *) cxt->aseen);

	av_undef(cxt->aclass);
	sv_free((SV *) cxt->aclass);

	hv_undef(cxt->hook);
	sv_free((SV *) cxt->hook);

	if (cxt->hseen)
		sv_free((SV *) cxt->hseen);		/* optional HV, for backward compat. */

	cxt->entry = 0;
	cxt->dirty = 0;
}

/*
 * clean_context
 *
 * A workaround for the CROAK bug: cleanup the last context.
 */
static void clean_context(cxt)
stcxt_t *cxt;
{
	TRACEME(("clean_context"));

	ASSERT(cxt->dirty, ("dirty context"));

	if (cxt->optype & ST_RETRIEVE)
		clean_retrieve_context(cxt);
	else
		clean_store_context(cxt);
}

/*
 * allocate_context
 *
 * Allocate a new context and push it on top of the parent one.
 * This new context is made globally visible via SET_STCXT().
 */
static stcxt_t *allocate_context(parent_cxt)
stcxt_t *parent_cxt;
{
	stcxt_t *cxt;

	TRACEME(("allocate_context"));

	ASSERT(!parent_cxt->dirty, ("parent context clean"));

	Newz(0, cxt, 1, stcxt_t);
	cxt->prev = parent_cxt;
	SET_STCXT(cxt);

	return cxt;
}

/*
 * free_context
 *
 * Free current context, which cannot be the "root" one.
 * Make the context underneath globally visible via SET_STCXT().
 */
static void free_context(cxt)
stcxt_t *cxt;
{
	stcxt_t *prev = cxt->prev;

	TRACEME(("free_context"));

	ASSERT(!cxt->dirty, ("clean context"));
	ASSERT(prev, ("not freeing root context"));

	if (kbuf)
		Safefree(kbuf);
	if (mbase)
		Safefree(mbase);

	Safefree(cxt);
	SET_STCXT(prev);
}

/***
 *** Predicates.
 ***/

/*
 * is_storing
 *
 * Tells whether we're in the middle of a store operation.
 */
int is_storing()
{
	dSTCXT;

	return cxt->entry && (cxt->optype & ST_STORE);
}

/*
 * is_retrieving
 *
 * Tells whether we're in the middle of a retrieve operation.
 */
int is_retrieving()
{
	dSTCXT;

	return cxt->entry && (cxt->optype & ST_RETRIEVE);
}

/*
 * last_op_in_netorder
 *
 * Returns whether last operation was made using network order.
 *
 * This is typically out-of-band information that might prove useful
 * to people wishing to convert native to network order data when used.
 */
int last_op_in_netorder()
{
	dSTCXT;

	return cxt->netorder;
}

/***
 *** Hook lookup and calling routines.
 ***/

/*
 * pkg_fetchmeth
 *
 * A wrapper on gv_fetchmethod_autoload() which caches results.
 *
 * Returns the routine reference as an SV*, or null if neither the package
 * nor its ancestors know about the method.
 */
static SV *pkg_fetchmeth(cache, pkg, method)
HV *cache;
HV *pkg;
char *method;
{
	GV *gv;
	SV *sv;
	SV **svh;

	/*
	 * The following code is the same as the one performed by UNIVERSAL::can
	 * in the Perl core.
	 */

	gv = gv_fetchmethod_autoload(pkg, method, FALSE);
	if (gv && isGV(gv)) {
		sv = newRV((SV*) GvCV(gv));
		TRACEME(("%s->%s: 0x%lx", HvNAME(pkg), method, (unsigned long) sv));
	} else {
		sv = newSVsv(&PL_sv_undef);
		TRACEME(("%s->%s: not found", HvNAME(pkg), method));
	}

	/*
	 * Cache the result, ignoring failure: if we can't store the value,
	 * it just won't be cached.
	 */

	(void) hv_store(cache, HvNAME(pkg), strlen(HvNAME(pkg)), sv, 0);

	return SvOK(sv) ? sv : (SV *) 0;
}

/*
 * pkg_hide
 *
 * Force cached value to be undef: hook ignored even if present.
 */
static void pkg_hide(cache, pkg, method)
HV *cache;
HV *pkg;
char *method;
{
	(void) hv_store(cache,
		HvNAME(pkg), strlen(HvNAME(pkg)), newSVsv(&PL_sv_undef), 0);
}

/*
 * pkg_can
 *
 * Our own "UNIVERSAL::can", which caches results.
 *
 * Returns the routine reference as an SV*, or null if the object does not
 * know about the method.
 */
static SV *pkg_can(cache, pkg, method)
HV *cache;
HV *pkg;
char *method;
{
	SV **svh;
	SV *sv;

	TRACEME(("pkg_can for %s->%s", HvNAME(pkg), method));

	/*
	 * Look into the cache to see whether we already have determined
	 * where the routine was, if any.
	 *
	 * NOTA BENE: we don't use `method' at all in our lookup, since we know
	 * that only one hook (i.e. always the same) is cached in a given cache.
	 */

	svh = hv_fetch(cache, HvNAME(pkg), strlen(HvNAME(pkg)), FALSE);
	if (svh) {
		sv = *svh;
		if (!SvOK(sv)) {
			TRACEME(("cached %s->%s: not found", HvNAME(pkg), method));
			return (SV *) 0;
		} else {
			TRACEME(("cached %s->%s: 0x%lx", HvNAME(pkg), method,
				(unsigned long) sv));
			return sv;
		}
	}

	TRACEME(("not cached yet"));
	return pkg_fetchmeth(cache, pkg, method);		/* Fetch and cache */
}

/*
 * scalar_call
 *
 * Call routine as obj->hook(av) in scalar context.
 * Propagates the single returned value if not called in void context.
 */
static SV *scalar_call(obj, hook, cloning, av, flags)
SV *obj;
SV *hook;
int cloning;
AV *av;
I32 flags;
{
	dSP;
	int count;
	SV *sv = 0;

	TRACEME(("scalar_call (cloning=%d)", cloning));

	ENTER;
	SAVETMPS;

	PUSHMARK(sp);
	XPUSHs(obj);
	XPUSHs(sv_2mortal(newSViv(cloning)));		/* Cloning flag */
	if (av) {
		SV **ary = AvARRAY(av);
		int cnt = AvFILLp(av) + 1;
		int i;
		XPUSHs(ary[0]);							/* Frozen string */
		for (i = 1; i < cnt; i++) {
			TRACEME(("pushing arg #%d (0x%lx)...", i, (unsigned long) ary[i]));
			XPUSHs(sv_2mortal(newRV(ary[i])));
		}
	}
	PUTBACK;

	TRACEME(("calling..."));
	count = perl_call_sv(hook, flags);		/* Go back to Perl code */
	TRACEME(("count = %d", count));

	SPAGAIN;

	if (count) {
		sv = POPs;
		SvREFCNT_inc(sv);		/* We're returning it, must stay alive! */
	}

	PUTBACK;
	FREETMPS;
	LEAVE;

	return sv;
}

/*
 * array_call
 *
 * Call routine obj->hook(cloning) in list context.
 * Returns the list of returned values in an array.
 */
static AV *array_call(obj, hook, cloning)
SV *obj;
SV *hook;
int cloning;
{
	dSP;
	int count;
	AV *av;
	int i;

	TRACEME(("arrary_call (cloning=%d)", cloning));

	ENTER;
	SAVETMPS;

	PUSHMARK(sp);
	XPUSHs(obj);								/* Target object */
	XPUSHs(sv_2mortal(newSViv(cloning)));		/* Cloning flag */
	PUTBACK;

	count = perl_call_sv(hook, G_ARRAY);		/* Go back to Perl code */

	SPAGAIN;

	av = newAV();
	for (i = count - 1; i >= 0; i--) {
		SV *sv = POPs;
		av_store(av, i, SvREFCNT_inc(sv));
	}

	PUTBACK;
	FREETMPS;
	LEAVE;

	return av;
}

/*
 * known_class
 *
 * Lookup the class name in the `hclass' table and either assign it a new ID
 * or return the existing one, by filling in `classnum'.
 *
 * Return true if the class was known, false if the ID was just generated.
 */
static int known_class(cxt, name, len, classnum)
stcxt_t *cxt;
char *name;		/* Class name */
int len;		/* Name length */
I32 *classnum;
{
	SV **svh;
	HV *hclass = cxt->hclass;

	TRACEME(("known_class (%s)", name));

	/*
	 * Recall that we don't store pointers in this hash table, but tags.
	 * Therefore, we need LOW_32BITS() to extract the relevant parts.
	 */

	svh = hv_fetch(hclass, name, len, FALSE);
	if (svh) {
		*classnum = LOW_32BITS(*svh);
		return TRUE;
	}

	/*
	 * Unknown classname, we need to record it.
	 */

	cxt->classnum++;
	if (!hv_store(hclass, name, len, INT2PTR(SV*, cxt->classnum), 0))
		CROAK(("Unable to record new classname"));

	*classnum = cxt->classnum;
	return FALSE;
}

/***
 *** Sepcific store routines.
 ***/

/*
 * store_ref
 *
 * Store a reference.
 * Layout is SX_REF <object> or SX_OVERLOAD <object>.
 */
static int store_ref(cxt, sv)
stcxt_t *cxt;
SV *sv;
{
	TRACEME(("store_ref (0x%lx)", (unsigned long) sv));

	/*
	 * Follow reference, and check if target is overloaded.
	 */

	sv = SvRV(sv);

	if (SvOBJECT(sv)) {
		HV *stash = (HV *) SvSTASH(sv);
		if (stash && Gv_AMG(stash)) {
			TRACEME(("ref (0x%lx) is overloaded", (unsigned long) sv));
			PUTMARK(SX_OVERLOAD);
		} else
			PUTMARK(SX_REF);
	} else
		PUTMARK(SX_REF);

	return store(cxt, sv);
}

/*
 * store_scalar
 *
 * Store a scalar.
 *
 * Layout is SX_LSCALAR <length> <data>, SX_SCALAR <lenght> <data> or SX_UNDEF.
 * The <data> section is omitted if <length> is 0.
 *
 * If integer or double, the layout is SX_INTEGER <data> or SX_DOUBLE <data>.
 * Small integers (within [-127, +127]) are stored as SX_BYTE <byte>.
 */
static int store_scalar(cxt, sv)
stcxt_t *cxt;
SV *sv;
{
	IV iv;
	char *pv;
	STRLEN len;
	U32 flags = SvFLAGS(sv);			/* "cc -O" may put it in register */

	TRACEME(("store_scalar (0x%lx)", (unsigned long) sv));

	/*
	 * For efficiency, break the SV encapsulation by peaking at the flags
	 * directly without using the Perl macros to avoid dereferencing
	 * sv->sv_flags each time we wish to check the flags.
	 */

	if (!(flags & SVf_OK)) {			/* !SvOK(sv) */
		if (sv == &PL_sv_undef) {
			TRACEME(("immortal undef"));
			PUTMARK(SX_SV_UNDEF);
		} else {
			TRACEME(("undef at 0x%x", sv));
			PUTMARK(SX_UNDEF);
		}
		return 0;
	}

	/*
	 * Always store the string representation of a scalar if it exists.
	 * Gisle Aas provided me with this test case, better than a long speach:
	 *
	 *  perl -MDevel::Peek -le '$a="abc"; $a+0; Dump($a)'
	 *  SV = PVNV(0x80c8520)
	 *       REFCNT = 1
	 *       FLAGS = (NOK,POK,pNOK,pPOK)
	 *       IV = 0
	 *       NV = 0
	 *       PV = 0x80c83d0 "abc"\0
	 *       CUR = 3
	 *       LEN = 4
	 *
	 * Write SX_SCALAR, length, followed by the actual data.
	 *
	 * Otherwise, write an SX_BYTE, SX_INTEGER or an SX_DOUBLE as
	 * appropriate, followed by the actual (binary) data. A double
	 * is written as a string if network order, for portability.
	 *
	 * NOTE: instead of using SvNOK(sv), we test for SvNOKp(sv).
	 * The reason is that when the scalar value is tainted, the SvNOK(sv)
	 * value is false.
	 *
	 * The test for a read-only scalar with both POK and NOK set is meant
	 * to quickly detect &PL_sv_yes and &PL_sv_no without having to pay the
	 * address comparison for each scalar we store.
	 */

#define SV_MAYBE_IMMORTAL (SVf_READONLY|SVf_POK|SVf_NOK)

	if ((flags & SV_MAYBE_IMMORTAL) == SV_MAYBE_IMMORTAL) {
		if (sv == &PL_sv_yes) {
			TRACEME(("immortal yes"));
			PUTMARK(SX_SV_YES);
		} else if (sv == &PL_sv_no) {
			TRACEME(("immortal no"));
			PUTMARK(SX_SV_NO);
		} else {
			pv = SvPV(sv, len);			/* We know it's SvPOK */
			goto string;				/* Share code below */
		}
	} else if (flags & SVp_POK) {		/* SvPOKp(sv) => string */
		pv = SvPV(sv, len);

		/*
		 * Will come here from below with pv and len set if double & netorder,
		 * or from above if it was readonly, POK and NOK but neither &PL_sv_yes
		 * nor &PL_sv_no.
		 */
	string:

		STORE_SCALAR(pv, len);
		TRACEME(("ok (scalar 0x%lx '%s', length = %d)",
			(unsigned long) sv, SvPVX(sv), len));

	} else if (flags & SVp_NOK) {		/* SvNOKp(sv) => double */
		NV nv = SvNV(sv);

		/*
		 * Watch for number being an integer in disguise.
		 */
		if (nv == (NV) (iv = I_V(nv))) {
			TRACEME(("double %lf is actually integer %ld", nv, iv));
			goto integer;		/* Share code below */
		}

		if (cxt->netorder) {
			TRACEME(("double %lf stored as string", nv));
			pv = SvPV(sv, len);
			goto string;		/* Share code above */
		}

		PUTMARK(SX_DOUBLE);
		WRITE(&nv, sizeof(nv));

		TRACEME(("ok (double 0x%lx, value = %lf)", (unsigned long) sv, nv));

	} else if (flags & SVp_IOK) {		/* SvIOKp(sv) => integer */
		iv = SvIV(sv);

		/*
		 * Will come here from above with iv set if double is an integer.
		 */
	integer:

		/*
		 * Optimize small integers into a single byte, otherwise store as
		 * a real integer (converted into network order if they asked).
		 */

		if (iv >= -128 && iv <= 127) {
			unsigned char siv = (unsigned char) (iv + 128);	/* [0,255] */
			PUTMARK(SX_BYTE);
			PUTMARK(siv);
			TRACEME(("small integer stored as %d", siv));
		} else if (cxt->netorder) {
			int niv;
#ifdef HAS_HTONL
			niv = (int) htonl(iv);
			TRACEME(("using network order"));
#else
			niv = (int) iv;
			TRACEME(("as-is for network order"));
#endif
			PUTMARK(SX_NETINT);
			WRITE(&niv, sizeof(niv));
		} else {
			PUTMARK(SX_INTEGER);
			WRITE(&iv, sizeof(iv));
		}

		TRACEME(("ok (integer 0x%lx, value = %d)", (unsigned long) sv, iv));

	} else
		CROAK(("Can't determine type of %s(0x%lx)", sv_reftype(sv, FALSE),
			(unsigned long) sv));

	return 0;		/* Ok, no recursion on scalars */
}

/*
 * store_array
 *
 * Store an array.
 *
 * Layout is SX_ARRAY <size> followed by each item, in increading index order.
 * Each item is stored as <object>.
 */
static int store_array(cxt, av)
stcxt_t *cxt;
AV *av;
{
	SV **sav;
	I32 len = av_len(av) + 1;
	I32 i;
	int ret;

	TRACEME(("store_array (0x%lx)", (unsigned long) av));

	/* 
	 * Signal array by emitting SX_ARRAY, followed by the array length.
	 */

	PUTMARK(SX_ARRAY);
	WLEN(len);
	TRACEME(("size = %d", len));

	/*
	 * Now store each item recursively.
	 */

	for (i = 0; i < len; i++) {
		sav = av_fetch(av, i, 0);
		if (!sav) {
			TRACEME(("(#%d) undef item", i));
			STORE_UNDEF();
			continue;
		}
		TRACEME(("(#%d) item", i));
		if (ret = store(cxt, *sav))
			return ret;
	}

	TRACEME(("ok (array)"));

	return 0;
}

/*
 * sortcmp
 *
 * Sort two SVs
 * Borrowed from perl source file pp_ctl.c, where it is used by pp_sort.
 */
static int
sortcmp(a, b)
const void *a;
const void *b;
{
	return sv_cmp(*(SV * const *) a, *(SV * const *) b);
}


/*
 * store_hash
 *
 * Store an hash table.
 *
 * Layout is SX_HASH <size> followed by each key/value pair, in random order.
 * Values are stored as <object>.
 * Keys are stored as <length> <data>, the <data> section being omitted
 * if length is 0.
 */
static int store_hash(cxt, hv)
stcxt_t *cxt;
HV *hv;
{
	I32 len = HvKEYS(hv);
	I32 i;
	int ret = 0;
	I32 riter;
	HE *eiter;

	TRACEME(("store_hash (0x%lx)", (unsigned long) hv));

	/* 
	 * Signal hash by emitting SX_HASH, followed by the table length.
	 */

	PUTMARK(SX_HASH);
	WLEN(len);
	TRACEME(("size = %d", len));

	/*
	 * Save possible iteration state via each() on that table.
	 */

	riter = HvRITER(hv);
	eiter = HvEITER(hv);
	hv_iterinit(hv);

	/*
	 * Now store each item recursively.
	 *
     * If canonical is defined to some true value then store each
     * key/value pair in sorted order otherwise the order is random.
	 * Canonical order is irrelevant when a deep clone operation is performed.
	 *
	 * Fetch the value from perl only once per store() operation, and only
	 * when needed.
	 */

	if (
		!(cxt->optype & ST_CLONE) && (cxt->canonical == 1 ||
		(cxt->canonical < 0 && (cxt->canonical =
			SvTRUE(perl_get_sv("Storable::canonical", TRUE)) ? 1 : 0)))
	) {
		/*
		 * Storing in order, sorted by key.
		 * Run through the hash, building up an array of keys in a
		 * mortal array, sort the array and then run through the
		 * array.  
		 */

		AV *av = newAV();

		TRACEME(("using canonical order"));

		for (i = 0; i < len; i++) {
			HE *he = hv_iternext(hv);
			SV *key = hv_iterkeysv(he);
			av_store(av, AvFILLp(av)+1, key);	/* av_push(), really */
		}
			
		qsort((char *) AvARRAY(av), len, sizeof(SV *), sortcmp);

		for (i = 0; i < len; i++) {
			char *keyval;
			I32 keylen;
			SV *key = av_shift(av);
			HE *he  = hv_fetch_ent(hv, key, 0, 0);
			SV *val = HeVAL(he);
			if (val == 0)
				return 1;		/* Internal error, not I/O error */
			
			/*
			 * Store value first.
			 */
			
			TRACEME(("(#%d) value 0x%lx", i, (unsigned long) val));

			if (ret = store(cxt, val))
				goto out;

			/*
			 * Write key string.
			 * Keys are written after values to make sure retrieval
			 * can be optimal in terms of memory usage, where keys are
			 * read into a fixed unique buffer called kbuf.
			 * See retrieve_hash() for details.
			 */
			 
			keyval = hv_iterkey(he, &keylen);
			TRACEME(("(#%d) key '%s'", i, keyval));
			WLEN(keylen);
			if (keylen)
				WRITE(keyval, keylen);
		}

		/* 
		 * Free up the temporary array
		 */

		av_undef(av);
		sv_free((SV *) av);

	} else {

		/*
		 * Storing in "random" order (in the order the keys are stored
		 * within the the hash).  This is the default and will be faster!
		 */
  
		for (i = 0; i < len; i++) {
			char *key;
			I32 len;
			SV *val = hv_iternextsv(hv, &key, &len);

			if (val == 0)
				return 1;		/* Internal error, not I/O error */

			/*
			 * Store value first.
			 */

			TRACEME(("(#%d) value 0x%lx", i, (unsigned long) val));

			if (ret = store(cxt, val))
				goto out;

			/*
			 * Write key string.
			 * Keys are written after values to make sure retrieval
			 * can be optimal in terms of memory usage, where keys are
			 * read into a fixed unique buffer called kbuf.
			 * See retrieve_hash() for details.
			 */

			TRACEME(("(#%d) key '%s'", i, key));
			WLEN(len);
			if (len)
				WRITE(key, len);
		}
    }

	TRACEME(("ok (hash 0x%lx)", (unsigned long) hv));

out:
	HvRITER(hv) = riter;		/* Restore hash iterator state */
	HvEITER(hv) = eiter;

	return ret;
}

/*
 * store_tied
 *
 * When storing a tied object (be it a tied scalar, array or hash), we lay out
 * a special mark, followed by the underlying tied object. For instance, when
 * dealing with a tied hash, we store SX_TIED_HASH <hash object>, where
 * <hash object> stands for the serialization of the tied hash.
 */
static int store_tied(cxt, sv)
stcxt_t *cxt;
SV *sv;
{
	MAGIC *mg;
	int ret = 0;
	int svt = SvTYPE(sv);
	char mtype = 'P';

	TRACEME(("store_tied (0x%lx)", (unsigned long) sv));

	/*
	 * We have a small run-time penalty here because we chose to factorise
	 * all tieds objects into the same routine, and not have a store_tied_hash,
	 * a store_tied_array, etc...
	 *
	 * Don't use a switch() statement, as most compilers don't optimize that
	 * well for 2/3 values. An if() else if() cascade is just fine. We put
	 * tied hashes first, as they are the most likely beasts.
	 */

	if (svt == SVt_PVHV) {
		TRACEME(("tied hash"));
		PUTMARK(SX_TIED_HASH);			/* Introduces tied hash */
	} else if (svt == SVt_PVAV) {
		TRACEME(("tied array"));
		PUTMARK(SX_TIED_ARRAY);			/* Introduces tied array */
	} else {
		TRACEME(("tied scalar"));
		PUTMARK(SX_TIED_SCALAR);		/* Introduces tied scalar */
		mtype = 'q';
	}

	if (!(mg = mg_find(sv, mtype)))
		CROAK(("No magic '%c' found while storing tied %s", mtype,
			(svt == SVt_PVHV) ? "hash" :
				(svt == SVt_PVAV) ? "array" : "scalar"));

	/*
	 * The mg->mg_obj found by mg_find() above actually points to the
	 * underlying tied Perl object implementation. For instance, if the
	 * original SV was that of a tied array, then mg->mg_obj is an AV.
	 *
	 * Note that we store the Perl object as-is. We don't call its FETCH
	 * method along the way. At retrieval time, we won't call its STORE
	 * method either, but the tieing magic will be re-installed. In itself,
	 * that ensures that the tieing semantics are preserved since futher
	 * accesses on the retrieved object will indeed call the magic methods...
	 */

	if (ret = store(cxt, mg->mg_obj))
		return ret;

	TRACEME(("ok (tied)"));

	return 0;
}

/*
 * store_tied_item
 *
 * Stores a reference to an item within a tied structure:
 *
 *  . \$h{key}, stores both the (tied %h) object and 'key'.
 *  . \$a[idx], stores both the (tied @a) object and 'idx'.
 *
 * Layout is therefore either:
 *     SX_TIED_KEY <object> <key>
 *     SX_TIED_IDX <object> <index>
 */
static int store_tied_item(cxt, sv)
stcxt_t *cxt;
SV *sv;
{
	MAGIC *mg;
	int ret;

	TRACEME(("store_tied_item (0x%lx)", (unsigned long) sv));

	if (!(mg = mg_find(sv, 'p')))
		CROAK(("No magic 'p' found while storing reference to tied item"));

	/*
	 * We discriminate between \$h{key} and \$a[idx] via mg_ptr.
	 */

	if (mg->mg_ptr) {
		TRACEME(("store_tied_item: storing a ref to a tied hash item"));
		PUTMARK(SX_TIED_KEY);
		TRACEME(("store_tied_item: storing OBJ 0x%lx",
			(unsigned long) mg->mg_obj));

		if (ret = store(cxt, mg->mg_obj))
			return ret;

		TRACEME(("store_tied_item: storing PTR 0x%lx",
			(unsigned long) mg->mg_ptr));

		if (ret = store(cxt, (SV *) mg->mg_ptr))
			return ret;
	} else {
		I32 idx = mg->mg_len;

		TRACEME(("store_tied_item: storing a ref to a tied array item "));
		PUTMARK(SX_TIED_IDX);
		TRACEME(("store_tied_item: storing OBJ 0x%lx",
			(unsigned long) mg->mg_obj));

		if (ret = store(cxt, mg->mg_obj))
			return ret;

		TRACEME(("store_tied_item: storing IDX %d", idx));

		WLEN(idx);
	}

	TRACEME(("ok (tied item)"));

	return 0;
}

/*
 * store_hook		-- dispatched manually, not via sv_store[]
 *
 * The blessed SV is serialized by a hook.
 *
 * Simple Layout is:
 *
 *     SX_HOOK <flags> <len> <classname> <len2> <str> [<len3> <object-IDs>]
 *
 * where <flags> indicates how long <len>, <len2> and <len3> are, whether
 * the trailing part [] is present, the type of object (scalar, array or hash).
 * There is also a bit which says how the classname is stored between:
 *
 *     <len> <classname>
 *     <index>
 *
 * and when the <index> form is used (classname already seen), the "large
 * classname" bit in <flags> indicates how large the <index> is.
 * 
 * The serialized string returned by the hook is of length <len2> and comes
 * next.  It is an opaque string for us.
 *
 * Those <len3> object IDs which are listed last represent the extra references
 * not directly serialized by the hook, but which are linked to the object.
 *
 * When recursion is mandated to resolve object-IDs not yet seen, we have
 * instead, with <header> being flags with bits set to indicate the object type
 * and that recursion was indeed needed:
 *
 *     SX_HOOK <header> <object> <header> <object> <flags>
 *
 * that same header being repeated between serialized objects obtained through
 * recursion, until we reach flags indicating no recursion, at which point
 * we know we've resynchronized with a single layout, after <flags>.
 */
static int store_hook(cxt, sv, type, pkg, hook)
stcxt_t *cxt;
SV *sv;
HV *pkg;
SV *hook;
{
	I32 len;
	char *class;
	STRLEN len2;
	SV *ref;
	AV *av;
	SV **ary;
	int count;				/* really len3 + 1 */
	unsigned char flags;
	char *pv;
	int i;
	int recursed = 0;		/* counts recursion */
	int obj_type;			/* object type, on 2 bits */
	I32 classnum;
	int ret;
	int clone = cxt->optype & ST_CLONE;

	TRACEME(("store_hook, class \"%s\", tagged #%d", HvNAME(pkg), cxt->tagnum));

	/*
	 * Determine object type on 2 bits.
	 */

	switch (type) {
	case svis_SCALAR:
		obj_type = SHT_SCALAR;
		break;
	case svis_ARRAY:
		obj_type = SHT_ARRAY;
		break;
	case svis_HASH:
		obj_type = SHT_HASH;
		break;
	default:
		CROAK(("Unexpected object type (%d) in store_hook()", type));
	}
	flags = SHF_NEED_RECURSE | obj_type;

	class = HvNAME(pkg);
	len = strlen(class);

	/*
	 * To call the hook, we need to fake a call like:
	 *
	 *    $object->STORABLE_freeze($cloning);
	 *
	 * but we don't have the $object here.  For instance, if $object is
	 * a blessed array, what we have in `sv' is the array, and we can't
	 * call a method on those.
	 *
	 * Therefore, we need to create a temporary reference to the object and
	 * make the call on that reference.
	 */

	TRACEME(("about to call STORABLE_freeze on class %s", class));

	ref = newRV_noinc(sv);				/* Temporary reference */
	av = array_call(ref, hook, clone);	/* @a = $object->STORABLE_freeze($c) */
	SvRV(ref) = 0;
	SvREFCNT_dec(ref);					/* Reclaim temporary reference */

	count = AvFILLp(av) + 1;
	TRACEME(("store_hook, array holds %d items", count));

	/*
	 * If they return an empty list, it means they wish to ignore the
	 * hook for this class (and not just this instance -- that's for them
	 * to handle if they so wish).
	 *
	 * Simply disable the cached entry for the hook (it won't be recomputed
	 * since it's present in the cache) and recurse to store_blessed().
	 */

	if (!count) {
		/*
		 * They must not change their mind in the middle of a serialization.
		 */

		if (hv_fetch(cxt->hclass, class, len, FALSE))
			CROAK(("Too late to ignore hooks for %s class \"%s\"",
				(cxt->optype & ST_CLONE) ? "cloning" : "storing", class));
	
		pkg_hide(cxt->hook, pkg, "STORABLE_freeze");

		ASSERT(!pkg_can(cxt->hook, pkg, "STORABLE_freeze"), ("hook invisible"));
		TRACEME(("Ignoring STORABLE_freeze in class \"%s\"", class));

		return store_blessed(cxt, sv, type, pkg);
	}

	/*
	 * Get frozen string.
	 */

	ary = AvARRAY(av);
	pv = SvPV(ary[0], len2);

	/*
	 * Allocate a class ID if not already done.
	 */

	if (!known_class(cxt, class, len, &classnum)) {
		TRACEME(("first time we see class %s, ID = %d", class, classnum));
		classnum = -1;				/* Mark: we must store classname */
	} else {
		TRACEME(("already seen class %s, ID = %d", class, classnum));
	}

	/*
	 * If they returned more than one item, we need to serialize some
	 * extra references if not already done.
	 *
	 * Loop over the array, starting at postion #1, and for each item,
	 * ensure it is a reference, serialize it if not already done, and
	 * replace the entry with the tag ID of the corresponding serialized
	 * object.
	 *
	 * We CHEAT by not calling av_fetch() and read directly within the
	 * array, for speed.
	 */

	for (i = 1; i < count; i++) {
		SV **svh;
		SV *xsv = ary[i];

		if (!SvROK(xsv))
			CROAK(("Item #%d from hook in %s is not a reference", i, class));
		xsv = SvRV(xsv);		/* Follow ref to know what to look for */

		/*
		 * Look in hseen and see if we have a tag already.
		 * Serialize entry if not done already, and get its tag.
		 */

		if (svh = hv_fetch(cxt->hseen, (char *) &xsv, sizeof(xsv), FALSE))
			goto sv_seen;		/* Avoid moving code too far to the right */

		TRACEME(("listed object %d at 0x%lx is unknown",
			i-1, (unsigned long) xsv));

		/*
		 * We need to recurse to store that object and get it to be known
		 * so that we can resolve the list of object-IDs at retrieve time.
		 *
		 * The first time we do this, we need to emit the proper header
		 * indicating that we recursed, and what the type of object is (the
		 * object we're storing via a user-hook).  Indeed, during retrieval,
		 * we'll have to create the object before recursing to retrieve the
		 * others, in case those would point back at that object.
		 */

		/* [SX_HOOK] <flags> <object>*/
		if (!recursed++)
			PUTMARK(SX_HOOK);
		PUTMARK(flags);

		if (ret = store(cxt, xsv))		/* Given by hook for us to store */
			return ret;

		svh = hv_fetch(cxt->hseen, (char *) &xsv, sizeof(xsv), FALSE);
		if (!svh)
			CROAK(("Could not serialize item #%d from hook in %s", i, class));

		/*
		 * Replace entry with its tag (not a real SV, so no refcnt increment)
		 */

	sv_seen:
		SvREFCNT_dec(xsv);
		ary[i] = *svh;
		TRACEME(("listed object %d at 0x%lx is tag #%d",
			i-1, (unsigned long) xsv, (I32) *svh));
	}

	/*
	 * Compute leading flags.
	 */

	flags = obj_type;
	if (((classnum == -1) ? len : classnum) > LG_SCALAR)
		flags |= SHF_LARGE_CLASSLEN;
	if (classnum != -1)
		flags |= SHF_IDX_CLASSNAME;
	if (len2 > LG_SCALAR)
		flags |= SHF_LARGE_STRLEN;
	if (count > 1)
		flags |= SHF_HAS_LIST;
	if (count > (LG_SCALAR + 1))
		flags |= SHF_LARGE_LISTLEN;

	/* 
	 * We're ready to emit either serialized form:
	 *
	 *   SX_HOOK <flags> <len> <classname> <len2> <str> [<len3> <object-IDs>]
	 *   SX_HOOK <flags> <index>           <len2> <str> [<len3> <object-IDs>]
	 *
	 * If we recursed, the SX_HOOK has already been emitted.
	 */

	TRACEME(("SX_HOOK (recursed=%d) flags=0x%x class=%d len=%d len2=%d len3=%d",
		recursed, flags, classnum, len, len2, count-1));

	/* SX_HOOK <flags> */
	if (!recursed)
		PUTMARK(SX_HOOK);
	PUTMARK(flags);

	/* <len> <classname> or <index> */
	if (flags & SHF_IDX_CLASSNAME) {
		if (flags & SHF_LARGE_CLASSLEN)
			WLEN(classnum);
		else {
			unsigned char cnum = (unsigned char) classnum;
			PUTMARK(cnum);
		}
	} else {
		if (flags & SHF_LARGE_CLASSLEN)
			WLEN(len);
		else {
			unsigned char clen = (unsigned char) len;
			PUTMARK(clen);
		}
		WRITE(class, len);		/* Final \0 is omitted */
	}

	/* <len2> <frozen-str> */
	if (flags & SHF_LARGE_STRLEN)
		WLEN(len2);
	else {
		unsigned char clen = (unsigned char) len2;
		PUTMARK(clen);
	}
	if (len2)
		WRITE(pv, len2);	/* Final \0 is omitted */

	/* [<len3> <object-IDs>] */
	if (flags & SHF_HAS_LIST) {
		int len3 = count - 1;
		if (flags & SHF_LARGE_LISTLEN)
			WLEN(len3);
		else {
			unsigned char clen = (unsigned char) len3;
			PUTMARK(clen);
		}

		/*
		 * NOTA BENE, for 64-bit machines: the ary[i] below does not yield a
		 * real pointer, rather a tag number, well under the 32-bit limit.
		 */

		for (i = 1; i < count; i++) {
			I32 tagval = htonl(LOW_32BITS(ary[i]));
			WRITE(&tagval, sizeof(I32));
			TRACEME(("object %d, tag #%d", i-1, ntohl(tagval)));
		}
	}

	/*
	 * Free the array.  We need extra care for indices after 0, since they
	 * don't hold real SVs but integers cast.
	 */

	if (count > 1)
		AvFILLp(av) = 0;	/* Cheat, nothing after 0 interests us */
	av_undef(av);
	sv_free((SV *) av);

	return 0;
}

/*
 * store_blessed	-- dispatched manually, not via sv_store[]
 *
 * Check whether there is a STORABLE_xxx hook defined in the class or in one
 * of its ancestors.  If there is, then redispatch to store_hook();
 *
 * Otherwise, the blessed SV is stored using the following layout:
 *
 *    SX_BLESS <flag> <len> <classname> <object>
 *
 * where <flag> indicates whether <len> is stored on 0 or 4 bytes, depending
 * on the high-order bit in flag: if 1, then length follows on 4 bytes.
 * Otherwise, the low order bits give the length, thereby giving a compact
 * representation for class names less than 127 chars long.
 *
 * Each <classname> seen is remembered and indexed, so that the next time
 * an object in the blessed in the same <classname> is stored, the following
 * will be emitted:
 *
 *    SX_IX_BLESS <flag> <index> <object>
 *
 * where <index> is the classname index, stored on 0 or 4 bytes depending
 * on the high-order bit in flag (same encoding as above for <len>).
 */
static int store_blessed(cxt, sv, type, pkg)
stcxt_t *cxt;
SV *sv;
int type;
HV *pkg;
{
	SV *hook;
	I32 len;
	char *class;
	I32 classnum;

	TRACEME(("store_blessed, type %d, class \"%s\"", type, HvNAME(pkg)));

	/*
	 * Look for a hook for this blessed SV and redirect to store_hook()
	 * if needed.
	 */

	hook = pkg_can(cxt->hook, pkg, "STORABLE_freeze");
	if (hook)
		return store_hook(cxt, sv, type, pkg, hook);

	/*
	 * This is a blessed SV without any serialization hook.
	 */

	class = HvNAME(pkg);
	len = strlen(class);

	TRACEME(("blessed 0x%lx in %s, no hook: tagged #%d",
		(unsigned long) sv, class, cxt->tagnum));

	/*
	 * Determine whether it is the first time we see that class name (in which
	 * case it will be stored in the SX_BLESS form), or whether we already
	 * saw that class name before (in which case the SX_IX_BLESS form will be
	 * used).
	 */

	if (known_class(cxt, class, len, &classnum)) {
		TRACEME(("already seen class %s, ID = %d", class, classnum));
		PUTMARK(SX_IX_BLESS);
		if (classnum <= LG_BLESS) {
			unsigned char cnum = (unsigned char) classnum;
			PUTMARK(cnum);
		} else {
			unsigned char flag = (unsigned char) 0x80;
			PUTMARK(flag);
			WLEN(classnum);
		}
	} else {
		TRACEME(("first time we see class %s, ID = %d", class, classnum));
		PUTMARK(SX_BLESS);
		if (len <= LG_BLESS) {
			unsigned char clen = (unsigned char) len;
			PUTMARK(clen);
		} else {
			unsigned char flag = (unsigned char) 0x80;
			PUTMARK(flag);
			WLEN(len);					/* Don't BER-encode, this should be rare */
		}
		WRITE(class, len);				/* Final \0 is omitted */
	}

	/*
	 * Now emit the <object> part.
	 */

	return SV_STORE(type)(cxt, sv);
}

/*
 * store_other
 *
 * We don't know how to store the item we reached, so return an error condition.
 * (it's probably a GLOB, some CODE reference, etc...)
 *
 * If they defined the `forgive_me' variable at the Perl level to some
 * true value, then don't croak, just warn, and store a placeholder string
 * instead.
 */
static int store_other(cxt, sv)
stcxt_t *cxt;
SV *sv;
{
	STRLEN len;
	static char buf[80];

	TRACEME(("store_other"));

	/*
	 * Fetch the value from perl only once per store() operation.
	 */

	if (
		cxt->forgive_me == 0 ||
		(cxt->forgive_me < 0 && !(cxt->forgive_me =
			SvTRUE(perl_get_sv("Storable::forgive_me", TRUE)) ? 1 : 0))
	)
		CROAK(("Can't store %s items", sv_reftype(sv, FALSE)));

	warn("Can't store item %s(0x%lx)",
		sv_reftype(sv, FALSE), (unsigned long) sv);

	/*
	 * Store placeholder string as a scalar instead...
	 */

	(void) sprintf(buf, "You lost %s(0x%lx)\0", sv_reftype(sv, FALSE),
		(unsigned long) sv);

	len = strlen(buf);
	STORE_SCALAR(buf, len);
	TRACEME(("ok (dummy \"%s\", length = %d)", buf, len));

	return 0;
}

/***
 *** Store driving routines
 ***/

/*
 * sv_type
 *
 * WARNING: partially duplicates Perl's sv_reftype for speed.
 *
 * Returns the type of the SV, identified by an integer. That integer
 * may then be used to index the dynamic routine dispatch table.
 */
static int sv_type(sv)
SV *sv;
{
	switch (SvTYPE(sv)) {
	case SVt_NULL:
	case SVt_IV:
	case SVt_NV:
		/*
		 * No need to check for ROK, that can't be set here since there
		 * is no field capable of hodling the xrv_rv reference.
		 */
		return svis_SCALAR;
	case SVt_PV:
	case SVt_RV:
	case SVt_PVIV:
	case SVt_PVNV:
		/*
		 * Starting from SVt_PV, it is possible to have the ROK flag
		 * set, the pointer to the other SV being either stored in
		 * the xrv_rv (in the case of a pure SVt_RV), or as the
		 * xpv_pv field of an SVt_PV and its heirs.
		 *
		 * However, those SV cannot be magical or they would be an
		 * SVt_PVMG at least.
		 */
		return SvROK(sv) ? svis_REF : svis_SCALAR;
	case SVt_PVMG:
	case SVt_PVLV:		/* Workaround for perl5.004_04 "LVALUE" bug */
		if (SvRMAGICAL(sv) && (mg_find(sv, 'p')))
			return svis_TIED_ITEM;
		/* FALL THROUGH */
	case SVt_PVBM:
		if (SvRMAGICAL(sv) && (mg_find(sv, 'q')))
			return svis_TIED;
		return SvROK(sv) ? svis_REF : svis_SCALAR;
	case SVt_PVAV:
		if (SvRMAGICAL(sv) && (mg_find(sv, 'P')))
			return svis_TIED;
		return svis_ARRAY;
	case SVt_PVHV:
		if (SvRMAGICAL(sv) && (mg_find(sv, 'P')))
			return svis_TIED;
		return svis_HASH;
	default:
		break;
	}

	return svis_OTHER;
}

/*
 * store
 *
 * Recursively store objects pointed to by the sv to the specified file.
 *
 * Layout is <content> or SX_OBJECT <tagnum> if we reach an already stored
 * object (one for which storage has started -- it may not be over if we have
 * a self-referenced structure). This data set forms a stored <object>.
 */
static int store(cxt, sv)
stcxt_t *cxt;
SV *sv;
{
	SV **svh;
	int ret;
	SV *tag;
	int type;
    HV *hseen = cxt->hseen;

	TRACEME(("store (0x%lx)", (unsigned long) sv));

	/*
	 * If object has already been stored, do not duplicate data.
	 * Simply emit the SX_OBJECT marker followed by its tag data.
	 * The tag is always written in network order.
	 *
	 * NOTA BENE, for 64-bit machines: the "*svh" below does not yield a
	 * real pointer, rather a tag number (watch the insertion code below).
	 * That means it pobably safe to assume it is well under the 32-bit limit,
	 * and makes the truncation safe.
	 *		-- RAM, 14/09/1999
	 */

	svh = hv_fetch(hseen, (char *) &sv, sizeof(sv), FALSE);
	if (svh) {
		I32 tagval = htonl(LOW_32BITS(*svh));

		TRACEME(("object 0x%lx seen as #%d",
			(unsigned long) sv, ntohl(tagval)));

		PUTMARK(SX_OBJECT);
		WRITE(&tagval, sizeof(I32));
		return 0;
	}

	/*
	 * Allocate a new tag and associate it with the address of the sv being
	 * stored, before recursing...
	 *
	 * In order to avoid creating new SvIVs to hold the tagnum we just
	 * cast the tagnum to a SV pointer and store that in the hash.  This
	 * means that we must clean up the hash manually afterwards, but gives
	 * us a 15% throughput increase.
	 *
	 */

	cxt->tagnum++;
	if (!hv_store(hseen,
			(char *) &sv, sizeof(sv), INT2PTR(SV*, cxt->tagnum), 0))
		return -1;

	/*
	 * Store `sv' and everything beneath it, using appropriate routine.
	 * Abort immediately if we get a non-zero status back.
	 */

	type = sv_type(sv);

	TRACEME(("storing 0x%lx tag #%d, type %d...",
		(unsigned long) sv, cxt->tagnum, type));

	if (SvOBJECT(sv)) {
		HV *pkg = SvSTASH(sv);
		ret = store_blessed(cxt, sv, type, pkg);
	} else
		ret = SV_STORE(type)(cxt, sv);

	TRACEME(("%s (stored 0x%lx, refcnt=%d, %s)",
		ret ? "FAILED" : "ok", (unsigned long) sv,
		SvREFCNT(sv), sv_reftype(sv, FALSE)));

	return ret;
}

/*
 * magic_write
 *
 * Write magic number and system information into the file.
 * Layout is <magic> <network> [<len> <byteorder> <sizeof int> <sizeof long>
 * <sizeof ptr>] where <len> is the length of the byteorder hexa string.
 * All size and lenghts are written as single characters here.
 *
 * Note that no byte ordering info is emitted when <network> is true, since
 * integers will be emitted in network order in that case.
 */
static int magic_write(cxt)
stcxt_t *cxt;
{
	char buf[256];	/* Enough room for 256 hexa digits */
	unsigned char c;
	int use_network_order = cxt->netorder;

	TRACEME(("magic_write on fd=%d", cxt->fio ? fileno(cxt->fio) : -1));

	if (cxt->fio)
		WRITE(magicstr, strlen(magicstr));	/* Don't write final \0 */

	/*
	 * Starting with 0.6, the "use_network_order" byte flag is also used to
	 * indicate the version number of the binary image, encoded in the upper
	 * bits. The bit 0 is always used to indicate network order.
	 */

	c = (unsigned char)
		((use_network_order ? 0x1 : 0x0) | (STORABLE_BIN_MAJOR << 1));
	PUTMARK(c);

	/*
	 * Starting with 0.7, a full byte is dedicated to the minor version of
	 * the binary format, which is incremented only when new markers are
	 * introduced, for instance, but when backward compatibility is preserved.
	 */

	PUTMARK((unsigned char) STORABLE_BIN_MINOR);

	if (use_network_order)
		return 0;						/* Don't bother with byte ordering */

	sprintf(buf, "%lx", (unsigned long) BYTEORDER);
	c = (unsigned char) strlen(buf);
	PUTMARK(c);
	WRITE(buf, (unsigned int) c);		/* Don't write final \0 */
	PUTMARK((unsigned char) sizeof(int));
	PUTMARK((unsigned char) sizeof(long));
	PUTMARK((unsigned char) sizeof(char *));

	TRACEME(("ok (magic_write byteorder = 0x%lx [%d], I%d L%d P%d)",
		(unsigned long) BYTEORDER, (int) c,
		sizeof(int), sizeof(long), sizeof(char *)));

	return 0;
}

/*
 * do_store
 *
 * Common code for store operations.
 *
 * When memory store is requested (f = NULL) and a non null SV* is given in
 * `res', it is filled with a new SV created out of the memory buffer.
 *
 * It is required to provide a non-null `res' when the operation type is not
 * dclone() and store() is performed to memory.
 */
static int do_store(f, sv, optype, network_order, res)
PerlIO *f;
SV *sv;
int optype;
int network_order;
SV **res;
{
	dSTCXT;
	int status;

	ASSERT(!(f == 0 && !(optype & ST_CLONE)) || res,
		("must supply result SV pointer for real recursion to memory"));

	TRACEME(("do_store (optype=%d, netorder=%d)",
		optype, network_order));

	optype |= ST_STORE;

	/*
	 * Workaround for CROAK leak: if they enter with a "dirty" context,
	 * free up memory for them now.
	 */

	if (cxt->dirty)
		clean_context(cxt);

	/*
	 * Now that STORABLE_xxx hooks exist, it is possible that they try to
	 * re-enter store() via the hooks.  We need to stack contexts.
	 */

	if (cxt->entry)
		cxt = allocate_context(cxt);

	cxt->entry++;

	ASSERT(cxt->entry == 1, ("starting new recursion"));
	ASSERT(!cxt->dirty, ("clean context"));

	/*
	 * Ensure sv is actually a reference. From perl, we called something
	 * like:
	 *       pstore(FILE, \@array);
	 * so we must get the scalar value behing that reference.
	 */

	if (!SvROK(sv))
		CROAK(("Not a reference"));
	sv = SvRV(sv);			/* So follow it to know what to store */

	/* 
	 * If we're going to store to memory, reset the buffer.
	 */

	if (!f)
		MBUF_INIT(0);

	/*
	 * Prepare context and emit headers.
	 */

	init_store_context(cxt, f, optype, network_order);

	if (-1 == magic_write(cxt))		/* Emit magic and ILP info */
		return 0;					/* Error */

	/*
	 * Recursively store object...
	 */

	ASSERT(is_storing(), ("within store operation"));

	status = store(cxt, sv);		/* Just do it! */

	/*
	 * If they asked for a memory store and they provided an SV pointer,
	 * make an SV string out of the buffer and fill their pointer.
	 *
	 * When asking for ST_REAL, it's MANDATORY for the caller to provide
	 * an SV, since context cleanup might free the buffer if we did recurse.
	 * (unless caller is dclone(), which is aware of that).
	 */

	if (!cxt->fio && res)
		*res = mbuf2sv();

	/*
	 * Final cleanup.
	 *
	 * The "root" context is never freed, since it is meant to be always
	 * handy for the common case where no recursion occurs at all (i.e.
	 * we enter store() outside of any Storable code and leave it, period).
	 * We know it's the "root" context because there's nothing stacked
	 * underneath it.
	 *
	 * OPTIMIZATION:
	 *
	 * When deep cloning, we don't free the context: doing so would force
	 * us to copy the data in the memory buffer.  Sicne we know we're
	 * about to enter do_retrieve...
	 */

	clean_store_context(cxt);
	if (cxt->prev && !(cxt->optype & ST_CLONE))
		free_context(cxt);

	TRACEME(("do_store returns %d", status));

	return status == 0;
}

/*
 * pstore
 *
 * Store the transitive data closure of given object to disk.
 * Returns 0 on error, a true value otherwise.
 */
int pstore(f, sv)
PerlIO *f;
SV *sv;
{
	TRACEME(("pstore"));
	return do_store(f, sv, 0, FALSE, (SV**)0);

}

/*
 * net_pstore
 *
 * Same as pstore(), but network order is used for integers and doubles are
 * emitted as strings.
 */
int net_pstore(f, sv)
PerlIO *f;
SV *sv;
{
	TRACEME(("net_pstore"));
	return do_store(f, sv, 0, TRUE, (SV**)0);
}

/***
 *** Memory stores.
 ***/

/*
 * mbuf2sv
 *
 * Build a new SV out of the content of the internal memory buffer.
 */
static SV *mbuf2sv()
{
	dSTCXT;

	return newSVpv(mbase, MBUF_SIZE());
}

/*
 * mstore
 *
 * Store the transitive data closure of given object to memory.
 * Returns undef on error, a scalar value containing the data otherwise.
 */
SV *mstore(sv)
SV *sv;
{
	dSTCXT;
	SV *out;

	TRACEME(("mstore"));

	if (!do_store((PerlIO*)0, sv, 0, FALSE, &out))
		return &PL_sv_undef;

	return out;
}

/*
 * net_mstore
 *
 * Same as mstore(), but network order is used for integers and doubles are
 * emitted as strings.
 */
SV *net_mstore(sv)
SV *sv;
{
	dSTCXT;
	SV *out;

	TRACEME(("net_mstore"));

	if (!do_store((PerlIO*)0, sv, 0, TRUE, &out))
		return &PL_sv_undef;

	return out;
}

/***
 *** Specific retrieve callbacks.
 ***/

/*
 * retrieve_other
 *
 * Return an error via croak, since it is not possible that we get here
 * under normal conditions, when facing a file produced via pstore().
 */
static SV *retrieve_other(cxt)
stcxt_t *cxt;
{
	if (
		cxt->ver_major != STORABLE_BIN_MAJOR &&
		cxt->ver_minor != STORABLE_BIN_MINOR
	) {
		CROAK(("Corrupted storable %s (binary v%d.%d), current is v%d.%d",
			cxt->fio ? "file" : "string",
			cxt->ver_major, cxt->ver_minor,
			STORABLE_BIN_MAJOR, STORABLE_BIN_MINOR));
	} else {
		CROAK(("Corrupted storable %s (binary v%d.%d)",
			cxt->fio ? "file" : "string",
			cxt->ver_major, cxt->ver_minor));
	}

	return (SV *) 0;		/* Just in case */
}

/*
 * retrieve_idx_blessed
 *
 * Layout is SX_IX_BLESS <index> <object> with SX_IX_BLESS already read.
 * <index> can be coded on either 1 or 5 bytes.
 */
static SV *retrieve_idx_blessed(cxt)
stcxt_t *cxt;
{
	I32 idx;
	char *class;
	SV **sva;
	SV *sv;

	TRACEME(("retrieve_idx_blessed (#%d)", cxt->tagnum));

	GETMARK(idx);			/* Index coded on a single char? */
	if (idx & 0x80)
		RLEN(idx);

	/*
	 * Fetch classname in `aclass'
	 */

	sva = av_fetch(cxt->aclass, idx, FALSE);
	if (!sva)
		CROAK(("Class name #%d should have been seen already", idx));

	class = SvPVX(*sva);	/* We know it's a PV, by construction */

	TRACEME(("class ID %d => %s", idx, class));

	/*
	 * Retrieve object and bless it.
	 */

	sv = retrieve(cxt);
	if (sv)
		BLESS(sv, class);

	return sv;
}

/*
 * retrieve_blessed
 *
 * Layout is SX_BLESS <len> <classname> <object> with SX_BLESS already read.
 * <len> can be coded on either 1 or 5 bytes.
 */
static SV *retrieve_blessed(cxt)
stcxt_t *cxt;
{
	I32 len;
	SV *sv;
	char buf[LG_BLESS + 1];		/* Avoid malloc() if possible */
	char *class = buf;

	TRACEME(("retrieve_blessed (#%d)", cxt->tagnum));

	/*
	 * Decode class name length and read that name.
	 *
	 * Short classnames have two advantages: their length is stored on one
	 * single byte, and the string can be read on the stack.
	 */

	GETMARK(len);			/* Length coded on a single char? */
	if (len & 0x80) {
		RLEN(len);
		TRACEME(("** allocating %d bytes for class name", len+1));
		New(10003, class, len+1, char);
	}
	READ(class, len);
	class[len] = '\0';		/* Mark string end */

	/*
	 * It's a new classname, otherwise it would have been an SX_IX_BLESS.
	 */

	if (!av_store(cxt->aclass, cxt->classnum++, newSVpvn(class, len)))
		return (SV *) 0;

	/*
	 * Retrieve object and bless it.
	 */

	sv = retrieve(cxt);
	if (sv) {
		BLESS(sv, class);
		if (class != buf)
			Safefree(class);
	}

	return sv;
}

/*
 * retrieve_hook
 *
 * Layout: SX_HOOK <flags> <len> <classname> <len2> <str> [<len3> <object-IDs>]
 * with leading mark already read, as usual.
 *
 * When recursion was involved during serialization of the object, there
 * is an unknown amount of serialized objects after the SX_HOOK mark.  Until
 * we reach a <flags> marker with the recursion bit cleared.
 */
static SV *retrieve_hook(cxt)
stcxt_t *cxt;
{
	I32 len;
	char buf[LG_BLESS + 1];		/* Avoid malloc() if possible */
	char *class = buf;
	unsigned int flags;
	I32 len2;
	SV *frozen;
	I32 len3 = 0;
	AV *av = 0;
	SV *hook;
	SV *sv;
	SV *rv;
	int obj_type;
	I32 classname;
	int clone = cxt->optype & ST_CLONE;

	TRACEME(("retrieve_hook (#%d)", cxt->tagnum));

	/*
	 * Read flags, which tell us about the type, and whether we need to recurse.
	 */

	GETMARK(flags);

	/*
	 * Create the (empty) object, and mark it as seen.
	 *
	 * This must be done now, because tags are incremented, and during
	 * serialization, the object tag was affected before recursion could
	 * take place.
	 */

	obj_type = flags & SHF_TYPE_MASK;
	switch (obj_type) {
	case SHT_SCALAR:
		sv = newSV(0);
		break;
	case SHT_ARRAY:
		sv = (SV *) newAV();
		break;
	case SHT_HASH:
		sv = (SV *) newHV();
		break;
	default:
		return retrieve_other(cxt);		/* Let it croak */
	}
	SEEN(sv);

	/*
	 * Whilst flags tell us to recurse, do so.
	 *
	 * We don't need to remember the addresses returned by retrieval, because
	 * all the references will be obtained through indirection via the object
	 * tags in the object-ID list.
	 */

	while (flags & SHF_NEED_RECURSE) {
		TRACEME(("retrieve_hook recursing..."));
		rv = retrieve(cxt);
		if (!rv)
			return (SV *) 0;
		TRACEME(("retrieve_hook back with rv=0x%lx", (unsigned long) rv));
		GETMARK(flags);
	}

	if (flags & SHF_IDX_CLASSNAME) {
		SV **sva;
		I32 idx;

		/*
		 * Fetch index from `aclass'
		 */

		if (flags & SHF_LARGE_CLASSLEN)
			RLEN(idx);
		else
			GETMARK(idx);

		sva = av_fetch(cxt->aclass, idx, FALSE);
		if (!sva)
			CROAK(("Class name #%d should have been seen already", idx));

		class = SvPVX(*sva);	/* We know it's a PV, by construction */
		TRACEME(("class ID %d => %s", idx, class));

	} else {
		/*
		 * Decode class name length and read that name.
		 *
		 * NOTA BENE: even if the length is stored on one byte, we don't read
		 * on the stack.  Just like retrieve_blessed(), we limit the name to
		 * LG_BLESS bytes.  This is an arbitrary decision.
		 */

		if (flags & SHF_LARGE_CLASSLEN)
			RLEN(len);
		else
			GETMARK(len);

		if (len > LG_BLESS) {
			TRACEME(("** allocating %d bytes for class name", len+1));
			New(10003, class, len+1, char);
		}

		READ(class, len);
		class[len] = '\0';		/* Mark string end */

		/*
		 * Record new classname.
		 */

		if (!av_store(cxt->aclass, cxt->classnum++, newSVpvn(class, len)))
			return (SV *) 0;
	}

	TRACEME(("class name: %s", class));

	/*
	 * Decode user-frozen string length and read it in a SV.
	 *
	 * For efficiency reasons, we read data directly into the SV buffer.
	 * To understand that code, read retrieve_scalar()
	 */

	if (flags & SHF_LARGE_STRLEN)
		RLEN(len2);
	else
		GETMARK(len2);

	frozen = NEWSV(10002, len2);
	if (len2) {
		SAFEREAD(SvPVX(frozen), len2, frozen);
		SvCUR_set(frozen, len2);
		*SvEND(frozen) = '\0';
	}
	(void) SvPOK_only(frozen);		/* Validates string pointer */
	SvTAINT(frozen);

	TRACEME(("frozen string: %d bytes", len2));

	/*
	 * Decode object-ID list length, if present.
	 */

	if (flags & SHF_HAS_LIST) {
		if (flags & SHF_LARGE_LISTLEN)
			RLEN(len3);
		else
			GETMARK(len3);
		if (len3) {
			av = newAV();
			av_extend(av, len3 + 1);	/* Leave room for [0] */
			AvFILLp(av) = len3;			/* About to be filled anyway */
		}
	}

	TRACEME(("has %d object IDs to link", len3));

	/*
	 * Read object-ID list into array.
	 * Because we pre-extended it, we can cheat and fill it manually.
	 *
	 * We read object tags and we can convert them into SV* on the fly
	 * because we know all the references listed in there (as tags)
	 * have been already serialized, hence we have a valid correspondance
	 * between each of those tags and the recreated SV.
	 */

	if (av) {
		SV **ary = AvARRAY(av);
		int i;
		for (i = 1; i <= len3; i++) {	/* We leave [0] alone */
			I32 tag;
			SV **svh;
			SV *xsv;

			READ(&tag, sizeof(I32));
			tag = ntohl(tag);
			svh = av_fetch(cxt->aseen, tag, FALSE);
			if (!svh)
				CROAK(("Object #%d should have been retrieved already", tag));
			xsv = *svh;
			ary[i] = SvREFCNT_inc(xsv);
		}
	}

	/*
	 * Bless the object and look up the STORABLE_thaw hook.
	 */

	BLESS(sv, class);
	hook = pkg_can(cxt->hook, SvSTASH(sv), "STORABLE_thaw");
	if (!hook)
		CROAK(("No STORABLE_thaw defined for objects of class %s", class));

	/*
	 * If we don't have an `av' yet, prepare one.
	 * Then insert the frozen string as item [0].
	 */

	if (!av) {
		av = newAV();
		av_extend(av, 1);
		AvFILLp(av) = 0;
	}
	AvARRAY(av)[0] = SvREFCNT_inc(frozen);

	/*
	 * Call the hook as:
	 *
	 *   $object->STORABLE_thaw($cloning, $frozen, @refs);
	 * 
	 * where $object is our blessed (empty) object, $cloning is a boolean
	 * telling whether we're running a deep clone, $frozen is the frozen
	 * string the user gave us in his serializing hook, and @refs, which may
	 * be empty, is the list of extra references he returned along for us
	 * to serialize.
	 *
	 * In effect, the hook is an alternate creation routine for the class,
	 * the object itself being already created by the runtime.
	 */

	TRACEME(("calling STORABLE_thaw on %s at 0x%lx (%d args)",
		class, (unsigned long) sv, AvFILLp(av) + 1));

	rv = newRV(sv);
	(void) scalar_call(rv, hook, clone, av, G_SCALAR|G_DISCARD);
	SvREFCNT_dec(rv);

	/*
	 * Final cleanup.
	 */

	SvREFCNT_dec(frozen);
	av_undef(av);
	sv_free((SV *) av);
	if (!(flags & SHF_IDX_CLASSNAME) && class != buf)
		Safefree(class);

	return sv;
}

/*
 * retrieve_ref
 *
 * Retrieve reference to some other scalar.
 * Layout is SX_REF <object>, with SX_REF already read.
 */
static SV *retrieve_ref(cxt)
stcxt_t *cxt;
{
	SV *rv;
	SV *sv;

	TRACEME(("retrieve_ref (#%d)", cxt->tagnum));

	/*
	 * We need to create the SV that holds the reference to the yet-to-retrieve
	 * object now, so that we may record the address in the seen table.
	 * Otherwise, if the object to retrieve references us, we won't be able
	 * to resolve the SX_OBJECT we'll see at that point! Hence we cannot
	 * do the retrieve first and use rv = newRV(sv) since it will be too late
	 * for SEEN() recording.
	 */

	rv = NEWSV(10002, 0);
	SEEN(rv);				/* Will return if rv is null */
	sv = retrieve(cxt);		/* Retrieve <object> */
	if (!sv)
		return (SV *) 0;	/* Failed */

	/*
	 * WARNING: breaks RV encapsulation.
	 *
	 * Now for the tricky part. We have to upgrade our existing SV, so that
	 * it is now an RV on sv... Again, we cheat by duplicating the code
	 * held in newSVrv(), since we already got our SV from retrieve().
	 *
	 * We don't say:
	 *
	 *		SvRV(rv) = SvREFCNT_inc(sv);
	 *
	 * here because the reference count we got from retrieve() above is
	 * already correct: if the object was retrieved from the file, then
	 * its reference count is one. Otherwise, if it was retrieved via
	 * an SX_OBJECT indication, a ref count increment was done.
	 */

	sv_upgrade(rv, SVt_RV);
	SvRV(rv) = sv;				/* $rv = \$sv */
	SvROK_on(rv);

	TRACEME(("ok (retrieve_ref at 0x%lx)", (unsigned long) rv));

	return rv;
}

/*
 * retrieve_overloaded
 *
 * Retrieve reference to some other scalar with overloading.
 * Layout is SX_OVERLOAD <object>, with SX_OVERLOAD already read.
 */
static SV *retrieve_overloaded(cxt)
stcxt_t *cxt;
{
	SV *rv;
	SV *sv;
	HV *stash;

	TRACEME(("retrieve_overloaded (#%d)", cxt->tagnum));

	/*
	 * Same code as retrieve_ref(), duplicated to avoid extra call.
	 */

	rv = NEWSV(10002, 0);
	SEEN(rv);				/* Will return if rv is null */
	sv = retrieve(cxt);		/* Retrieve <object> */
	if (!sv)
		return (SV *) 0;	/* Failed */

	/*
	 * WARNING: breaks RV encapsulation.
	 */

	sv_upgrade(rv, SVt_RV);
	SvRV(rv) = sv;				/* $rv = \$sv */
	SvROK_on(rv);

	/*
	 * Restore overloading magic.
	 */

	stash = (HV *) SvSTASH (sv);
	if (!stash || !Gv_AMG(stash))
		CROAK(("Cannot restore overloading on %s(0x%lx)", sv_reftype(sv, FALSE),
			(unsigned long) sv));

	SvAMAGIC_on(rv);

	TRACEME(("ok (retrieve_overloaded at 0x%lx)", (unsigned long) rv));

	return rv;
}

/*
 * retrieve_tied_array
 *
 * Retrieve tied array
 * Layout is SX_TIED_ARRAY <object>, with SX_TIED_ARRAY already read.
 */
static SV *retrieve_tied_array(cxt)
stcxt_t *cxt;
{
	SV *tv;
	SV *sv;

	TRACEME(("retrieve_tied_array (#%d)", cxt->tagnum));

	tv = NEWSV(10002, 0);
	SEEN(tv);					/* Will return if tv is null */
	sv = retrieve(cxt);			/* Retrieve <object> */
	if (!sv)
		return (SV *) 0;		/* Failed */

	sv_upgrade(tv, SVt_PVAV);
	AvREAL_off((AV *)tv);
	sv_magic(tv, sv, 'P', Nullch, 0);
	SvREFCNT_dec(sv);			/* Undo refcnt inc from sv_magic() */

	TRACEME(("ok (retrieve_tied_array at 0x%lx)", (unsigned long) tv));

	return tv;
}

/*
 * retrieve_tied_hash
 *
 * Retrieve tied hash
 * Layout is SX_TIED_HASH <object>, with SX_TIED_HASH already read.
 */
static SV *retrieve_tied_hash(cxt)
stcxt_t *cxt;
{
	SV *tv;
	SV *sv;

	TRACEME(("retrieve_tied_hash (#%d)", cxt->tagnum));

	tv = NEWSV(10002, 0);
	SEEN(tv);					/* Will return if tv is null */
	sv = retrieve(cxt);			/* Retrieve <object> */
	if (!sv)
		return (SV *) 0;		/* Failed */

	sv_upgrade(tv, SVt_PVHV);
	sv_magic(tv, sv, 'P', Nullch, 0);
	SvREFCNT_dec(sv);			/* Undo refcnt inc from sv_magic() */

	TRACEME(("ok (retrieve_tied_hash at 0x%lx)", (unsigned long) tv));

	return tv;
}

/*
 * retrieve_tied_scalar
 *
 * Retrieve tied scalar
 * Layout is SX_TIED_SCALAR <object>, with SX_TIED_SCALAR already read.
 */
static SV *retrieve_tied_scalar(cxt)
stcxt_t *cxt;
{
	SV *tv;
	SV *sv;

	TRACEME(("retrieve_tied_scalar (#%d)", cxt->tagnum));

	tv = NEWSV(10002, 0);
	SEEN(tv);					/* Will return if rv is null */
	sv = retrieve(cxt);			/* Retrieve <object> */
	if (!sv)
		return (SV *) 0;		/* Failed */

	sv_upgrade(tv, SVt_PVMG);
	sv_magic(tv, sv, 'q', Nullch, 0);
	SvREFCNT_dec(sv);			/* Undo refcnt inc from sv_magic() */

	TRACEME(("ok (retrieve_tied_scalar at 0x%lx)", (unsigned long) tv));

	return tv;
}

/*
 * retrieve_tied_key
 *
 * Retrieve reference to value in a tied hash.
 * Layout is SX_TIED_KEY <object> <key>, with SX_TIED_KEY already read.
 */
static SV *retrieve_tied_key(cxt)
stcxt_t *cxt;
{
	SV *tv;
	SV *sv;
	SV *key;

	TRACEME(("retrieve_tied_key (#%d)", cxt->tagnum));

	tv = NEWSV(10002, 0);
	SEEN(tv);					/* Will return if tv is null */
	sv = retrieve(cxt);			/* Retrieve <object> */
	if (!sv)
		return (SV *) 0;		/* Failed */

	key = retrieve(cxt);		/* Retrieve <key> */
	if (!key)
		return (SV *) 0;		/* Failed */

	sv_upgrade(tv, SVt_PVMG);
	sv_magic(tv, sv, 'p', (char *)key, HEf_SVKEY);
	SvREFCNT_dec(key);			/* Undo refcnt inc from sv_magic() */
	SvREFCNT_dec(sv);			/* Undo refcnt inc from sv_magic() */

	return tv;
}

/*
 * retrieve_tied_idx
 *
 * Retrieve reference to value in a tied array.
 * Layout is SX_TIED_IDX <object> <idx>, with SX_TIED_IDX already read.
 */
static SV *retrieve_tied_idx(cxt)
stcxt_t *cxt;
{
	SV *tv;
	SV *sv;
	I32 idx;

	TRACEME(("retrieve_tied_idx (#%d)", cxt->tagnum));

	tv = NEWSV(10002, 0);
	SEEN(tv);					/* Will return if tv is null */
	sv = retrieve(cxt);			/* Retrieve <object> */
	if (!sv)
		return (SV *) 0;		/* Failed */

	RLEN(idx);					/* Retrieve <idx> */

	sv_upgrade(tv, SVt_PVMG);
	sv_magic(tv, sv, 'p', Nullch, idx);
	SvREFCNT_dec(sv);			/* Undo refcnt inc from sv_magic() */

	return tv;
}


/*
 * retrieve_lscalar
 *
 * Retrieve defined long (string) scalar.
 *
 * Layout is SX_LSCALAR <length> <data>, with SX_LSCALAR already read.
 * The scalar is "long" in that <length> is larger than LG_SCALAR so it
 * was not stored on a single byte.
 */
static SV *retrieve_lscalar(cxt)
stcxt_t *cxt;
{
	STRLEN len;
	SV *sv;

	RLEN(len);
	TRACEME(("retrieve_lscalar (#%d), len = %d", cxt->tagnum, len));

	/*
	 * Allocate an empty scalar of the suitable length.
	 */

	sv = NEWSV(10002, len);
	SEEN(sv);			/* Associate this new scalar with tag "tagnum" */

	/*
	 * WARNING: duplicates parts of sv_setpv and breaks SV data encapsulation.
	 *
	 * Now, for efficiency reasons, read data directly inside the SV buffer,
	 * and perform the SV final settings directly by duplicating the final
	 * work done by sv_setpv. Since we're going to allocate lots of scalars
	 * this way, it's worth the hassle and risk.
	 */

	SAFEREAD(SvPVX(sv), len, sv);
	SvCUR_set(sv, len);				/* Record C string length */
	*SvEND(sv) = '\0';				/* Ensure it's null terminated anyway */
	(void) SvPOK_only(sv);			/* Validate string pointer */
	SvTAINT(sv);					/* External data cannot be trusted */

	TRACEME(("large scalar len %d '%s'", len, SvPVX(sv)));
	TRACEME(("ok (retrieve_lscalar at 0x%lx)", (unsigned long) sv));

	return sv;
}

/*
 * retrieve_scalar
 *
 * Retrieve defined short (string) scalar.
 *
 * Layout is SX_SCALAR <length> <data>, with SX_SCALAR already read.
 * The scalar is "short" so <length> is single byte. If it is 0, there
 * is no <data> section.
 */
static SV *retrieve_scalar(cxt)
stcxt_t *cxt;
{
	int len;
	SV *sv;

	GETMARK(len);
	TRACEME(("retrieve_scalar (#%d), len = %d", cxt->tagnum, len));

	/*
	 * Allocate an empty scalar of the suitable length.
	 */

	sv = NEWSV(10002, len);
	SEEN(sv);			/* Associate this new scalar with tag "tagnum" */

	/*
	 * WARNING: duplicates parts of sv_setpv and breaks SV data encapsulation.
	 */

	if (len == 0) {
		/*
		 * newSV did not upgrade to SVt_PV so the scalar is undefined.
		 * To make it defined with an empty length, upgrade it now...
		 */
		sv_upgrade(sv, SVt_PV);
		SvGROW(sv, 1);
		*SvEND(sv) = '\0';			/* Ensure it's null terminated anyway */
		TRACEME(("ok (retrieve_scalar empty at 0x%lx)", (unsigned long) sv));
	} else {
		/*
		 * Now, for efficiency reasons, read data directly inside the SV buffer,
		 * and perform the SV final settings directly by duplicating the final
		 * work done by sv_setpv. Since we're going to allocate lots of scalars
		 * this way, it's worth the hassle and risk.
		 */
		SAFEREAD(SvPVX(sv), len, sv);
		SvCUR_set(sv, len);			/* Record C string length */
		*SvEND(sv) = '\0';			/* Ensure it's null terminated anyway */
		TRACEME(("small scalar len %d '%s'", len, SvPVX(sv)));
	}

	(void) SvPOK_only(sv);			/* Validate string pointer */
	SvTAINT(sv);					/* External data cannot be trusted */

	TRACEME(("ok (retrieve_scalar at 0x%lx)", (unsigned long) sv));
	return sv;
}

/*
 * retrieve_integer
 *
 * Retrieve defined integer.
 * Layout is SX_INTEGER <data>, whith SX_INTEGER already read.
 */
static SV *retrieve_integer(cxt)
stcxt_t *cxt;
{
	SV *sv;
	IV iv;

	TRACEME(("retrieve_integer (#%d)", cxt->tagnum));

	READ(&iv, sizeof(iv));
	sv = newSViv(iv);
	SEEN(sv);			/* Associate this new scalar with tag "tagnum" */

	TRACEME(("integer %d", iv));
	TRACEME(("ok (retrieve_integer at 0x%lx)", (unsigned long) sv));

	return sv;
}

/*
 * retrieve_netint
 *
 * Retrieve defined integer in network order.
 * Layout is SX_NETINT <data>, whith SX_NETINT already read.
 */
static SV *retrieve_netint(cxt)
stcxt_t *cxt;
{
	SV *sv;
	int iv;

	TRACEME(("retrieve_netint (#%d)", cxt->tagnum));

	READ(&iv, sizeof(iv));
#ifdef HAS_NTOHL
	sv = newSViv((int) ntohl(iv));
	TRACEME(("network integer %d", (int) ntohl(iv)));
#else
	sv = newSViv(iv);
	TRACEME(("network integer (as-is) %d", iv));
#endif
	SEEN(sv);			/* Associate this new scalar with tag "tagnum" */

	TRACEME(("ok (retrieve_netint at 0x%lx)", (unsigned long) sv));

	return sv;
}

/*
 * retrieve_double
 *
 * Retrieve defined double.
 * Layout is SX_DOUBLE <data>, whith SX_DOUBLE already read.
 */
static SV *retrieve_double(cxt)
stcxt_t *cxt;
{
	SV *sv;
	NV nv;

	TRACEME(("retrieve_double (#%d)", cxt->tagnum));

	READ(&nv, sizeof(nv));
	sv = newSVnv(nv);
	SEEN(sv);			/* Associate this new scalar with tag "tagnum" */

	TRACEME(("double %lf", nv));
	TRACEME(("ok (retrieve_double at 0x%lx)", (unsigned long) sv));

	return sv;
}

/*
 * retrieve_byte
 *
 * Retrieve defined byte (small integer within the [-128, +127] range).
 * Layout is SX_BYTE <data>, whith SX_BYTE already read.
 */
static SV *retrieve_byte(cxt)
stcxt_t *cxt;
{
	SV *sv;
	int siv;

	TRACEME(("retrieve_byte (#%d)", cxt->tagnum));

	GETMARK(siv);
	TRACEME(("small integer read as %d", (unsigned char) siv));
	sv = newSViv((unsigned char) siv - 128);
	SEEN(sv);			/* Associate this new scalar with tag "tagnum" */

	TRACEME(("byte %d", (unsigned char) siv - 128));
	TRACEME(("ok (retrieve_byte at 0x%lx)", (unsigned long) sv));

	return sv;
}

/*
 * retrieve_undef
 *
 * Return the undefined value.
 */
static SV *retrieve_undef(cxt)
stcxt_t *cxt;
{
	SV* sv;

	TRACEME(("retrieve_undef"));

	sv = newSV(0);
	SEEN(sv);

	return sv;
}

/*
 * retrieve_sv_undef
 *
 * Return the immortal undefined value.
 */
static SV *retrieve_sv_undef(cxt)
stcxt_t *cxt;
{
	SV *sv = &PL_sv_undef;

	TRACEME(("retrieve_sv_undef"));

	SEEN(sv);
	return sv;
}

/*
 * retrieve_sv_yes
 *
 * Return the immortal yes value.
 */
static SV *retrieve_sv_yes(cxt)
stcxt_t *cxt;
{
	SV *sv = &PL_sv_yes;

	TRACEME(("retrieve_sv_yes"));

	SEEN(sv);
	return sv;
}

/*
 * retrieve_sv_no
 *
 * Return the immortal no value.
 */
static SV *retrieve_sv_no(cxt)
stcxt_t *cxt;
{
	SV *sv = &PL_sv_no;

	TRACEME(("retrieve_sv_no"));

	SEEN(sv);
	return sv;
}

/*
 * retrieve_array
 *
 * Retrieve a whole array.
 * Layout is SX_ARRAY <size> followed by each item, in increading index order.
 * Each item is stored as <object>.
 *
 * When we come here, SX_ARRAY has been read already.
 */
static SV *retrieve_array(cxt)
stcxt_t *cxt;
{
	I32 len;
	I32 i;
	AV *av;
	SV *sv;

	TRACEME(("retrieve_array (#%d)", cxt->tagnum));

	/*
	 * Read length, and allocate array, then pre-extend it.
	 */

	RLEN(len);
	TRACEME(("size = %d", len));
	av = newAV();
	SEEN(av);					/* Will return if array not allocated nicely */
	if (len)
		av_extend(av, len);
	else
		return (SV *) av;		/* No data follow if array is empty */

	/*
	 * Now get each item in turn...
	 */

	for (i = 0; i < len; i++) {
		TRACEME(("(#%d) item", i));
		sv = retrieve(cxt);				/* Retrieve item */
		if (!sv)
			return (SV *) 0;
		if (av_store(av, i, sv) == 0)
			return (SV *) 0;
	}

	TRACEME(("ok (retrieve_array at 0x%lx)", (unsigned long) av));

	return (SV *) av;
}

/*
 * retrieve_hash
 *
 * Retrieve a whole hash table.
 * Layout is SX_HASH <size> followed by each key/value pair, in random order.
 * Keys are stored as <length> <data>, the <data> section being omitted
 * if length is 0.
 * Values are stored as <object>.
 *
 * When we come here, SX_HASH has been read already.
 */
static SV *retrieve_hash(cxt)
stcxt_t *cxt;
{
	I32 len;
	I32 size;
	I32 i;
	HV *hv;
	SV *sv;
	static SV *sv_h_undef = (SV *) 0;		/* hv_store() bug */

	TRACEME(("retrieve_hash (#%d)", cxt->tagnum));

	/*
	 * Read length, allocate table.
	 */

	RLEN(len);
	TRACEME(("size = %d", len));
	hv = newHV();
	SEEN(hv);			/* Will return if table not allocated properly */
	if (len == 0)
		return (SV *) hv;	/* No data follow if table empty */

	/*
	 * Now get each key/value pair in turn...
	 */

	for (i = 0; i < len; i++) {
		/*
		 * Get value first.
		 */

		TRACEME(("(#%d) value", i));
		sv = retrieve(cxt);
		if (!sv)
			return (SV *) 0;

		/*
		 * Get key.
		 * Since we're reading into kbuf, we must ensure we're not
		 * recursing between the read and the hv_store() where it's used.
		 * Hence the key comes after the value.
		 */

		RLEN(size);						/* Get key size */
		KBUFCHK(size);					/* Grow hash key read pool if needed */
		if (size)
			READ(kbuf, size);
		kbuf[size] = '\0';				/* Mark string end, just in case */
		TRACEME(("(#%d) key '%s'", i, kbuf));

		/*
		 * Enter key/value pair into hash table.
		 */

		if (hv_store(hv, kbuf, (U32) size, sv, 0) == 0)
			return (SV *) 0;
	}

	TRACEME(("ok (retrieve_hash at 0x%lx)", (unsigned long) hv));

	return (SV *) hv;
}

/*
 * old_retrieve_array
 *
 * Retrieve a whole array in pre-0.6 binary format.
 *
 * Layout is SX_ARRAY <size> followed by each item, in increading index order.
 * Each item is stored as SX_ITEM <object> or SX_IT_UNDEF for "holes".
 *
 * When we come here, SX_ARRAY has been read already.
 */
static SV *old_retrieve_array(cxt)
stcxt_t *cxt;
{
	I32 len;
	I32 i;
	AV *av;
	SV *sv;
	int c;

	TRACEME(("old_retrieve_array (#%d)", cxt->tagnum));

	/*
	 * Read length, and allocate array, then pre-extend it.
	 */

	RLEN(len);
	TRACEME(("size = %d", len));
	av = newAV();
	SEEN(av);					/* Will return if array not allocated nicely */
	if (len)
		av_extend(av, len);
	else
		return (SV *) av;		/* No data follow if array is empty */

	/*
	 * Now get each item in turn...
	 */

	for (i = 0; i < len; i++) {
		GETMARK(c);
		if (c == SX_IT_UNDEF) {
			TRACEME(("(#%d) undef item", i));
			continue;			/* av_extend() already filled us with undef */
		}
		if (c != SX_ITEM)
			(void) retrieve_other(0);	/* Will croak out */
		TRACEME(("(#%d) item", i));
		sv = retrieve(cxt);				/* Retrieve item */
		if (!sv)
			return (SV *) 0;
		if (av_store(av, i, sv) == 0)
			return (SV *) 0;
	}

	TRACEME(("ok (old_retrieve_array at 0x%lx)", (unsigned long) av));

	return (SV *) av;
}

/*
 * old_retrieve_hash
 *
 * Retrieve a whole hash table in pre-0.6 binary format.
 *
 * Layout is SX_HASH <size> followed by each key/value pair, in random order.
 * Keys are stored as SX_KEY <length> <data>, the <data> section being omitted
 * if length is 0.
 * Values are stored as SX_VALUE <object> or SX_VL_UNDEF for "holes".
 *
 * When we come here, SX_HASH has been read already.
 */
static SV *old_retrieve_hash(cxt)
stcxt_t *cxt;
{
	I32 len;
	I32 size;
	I32 i;
	HV *hv;
	SV *sv;
	int c;
	static SV *sv_h_undef = (SV *) 0;		/* hv_store() bug */

	TRACEME(("old_retrieve_hash (#%d)", cxt->tagnum));

	/*
	 * Read length, allocate table.
	 */

	RLEN(len);
	TRACEME(("size = %d", len));
	hv = newHV();
	SEEN(hv);				/* Will return if table not allocated properly */
	if (len == 0)
		return (SV *) hv;	/* No data follow if table empty */

	/*
	 * Now get each key/value pair in turn...
	 */

	for (i = 0; i < len; i++) {
		/*
		 * Get value first.
		 */

		GETMARK(c);
		if (c == SX_VL_UNDEF) {
			TRACEME(("(#%d) undef value", i));
			/*
			 * Due to a bug in hv_store(), it's not possible to pass
			 * &PL_sv_undef to hv_store() as a value, otherwise the
			 * associated key will not be creatable any more. -- RAM, 14/01/97
			 */
			if (!sv_h_undef)
				sv_h_undef = newSVsv(&PL_sv_undef);
			sv = SvREFCNT_inc(sv_h_undef);
		} else if (c == SX_VALUE) {
			TRACEME(("(#%d) value", i));
			sv = retrieve(cxt);
			if (!sv)
				return (SV *) 0;
		} else
			(void) retrieve_other(0);	/* Will croak out */

		/*
		 * Get key.
		 * Since we're reading into kbuf, we must ensure we're not
		 * recursing between the read and the hv_store() where it's used.
		 * Hence the key comes after the value.
		 */

		GETMARK(c);
		if (c != SX_KEY)
			(void) retrieve_other(0);	/* Will croak out */
		RLEN(size);						/* Get key size */
		KBUFCHK(size);					/* Grow hash key read pool if needed */
		if (size)
			READ(kbuf, size);
		kbuf[size] = '\0';				/* Mark string end, just in case */
		TRACEME(("(#%d) key '%s'", i, kbuf));

		/*
		 * Enter key/value pair into hash table.
		 */

		if (hv_store(hv, kbuf, (U32) size, sv, 0) == 0)
			return (SV *) 0;
	}

	TRACEME(("ok (retrieve_hash at 0x%lx)", (unsigned long) hv));

	return (SV *) hv;
}

/***
 *** Retrieval engine.
 ***/

/*
 * magic_check
 *
 * Make sure the stored data we're trying to retrieve has been produced
 * on an ILP compatible system with the same byteorder. It croaks out in
 * case an error is detected. [ILP = integer-long-pointer sizes]
 * Returns null if error is detected, &PL_sv_undef otherwise.
 *
 * Note that there's no byte ordering info emitted when network order was
 * used at store time.
 */
static SV *magic_check(cxt)
stcxt_t *cxt;
{
	char buf[256];
	char byteorder[256];
	int c;
	int use_network_order;
	int version_major;
	int version_minor = 0;

	TRACEME(("magic_check"));

	/*
	 * The "magic number" is only for files, not when freezing in memory.
	 */

	if (cxt->fio) {
		STRLEN len = sizeof(magicstr) - 1;
		STRLEN old_len;

		READ(buf, len);					/* Not null-terminated */
		buf[len] = '\0';				/* Is now */

		if (0 == strcmp(buf, magicstr))
			goto magic_ok;

		/*
		 * Try to read more bytes to check for the old magic number, which
		 * was longer.
		 */

		old_len = sizeof(old_magicstr) - 1;
		READ(&buf[len], old_len - len);
		buf[old_len] = '\0';			/* Is now null-terminated */

		if (strcmp(buf, old_magicstr))
			CROAK(("File is not a perl storable"));
	}

magic_ok:
	/*
	 * Starting with 0.6, the "use_network_order" byte flag is also used to
	 * indicate the version number of the binary, and therefore governs the
	 * setting of sv_retrieve_vtbl. See magic_write().
	 */

	GETMARK(use_network_order);
	version_major = use_network_order >> 1;
	cxt->retrieve_vtbl = version_major ? sv_retrieve : sv_old_retrieve;

	TRACEME(("magic_check: netorder = 0x%x", use_network_order));


	/*
	 * Starting with 0.7 (binary major 2), a full byte is dedicated to the
	 * minor version of the protocol.  See magic_write().
	 */

	if (version_major > 1)
		GETMARK(version_minor);

	cxt->ver_major = version_major;
	cxt->ver_minor = version_minor;

	TRACEME(("binary image version is %d.%d", version_major, version_minor));

	/*
	 * Inter-operability sanity check: we can't retrieve something stored
	 * using a format more recent than ours, because we have no way to
	 * know what has changed, and letting retrieval go would mean a probable
	 * failure reporting a "corrupted" storable file.
	 */

	if (
		version_major > STORABLE_BIN_MAJOR ||
			(version_major == STORABLE_BIN_MAJOR &&
			version_minor > STORABLE_BIN_MINOR)
	)
		CROAK(("Storable binary image v%d.%d more recent than I am (v%d.%d)",
			version_major, version_minor,
			STORABLE_BIN_MAJOR, STORABLE_BIN_MINOR));

	/*
	 * If they stored using network order, there's no byte ordering
	 * information to check.
	 */

	if (cxt->netorder = (use_network_order & 0x1))
		return &PL_sv_undef;			/* No byte ordering info */

	sprintf(byteorder, "%lx", (unsigned long) BYTEORDER);
	GETMARK(c);
	READ(buf, c);						/* Not null-terminated */
	buf[c] = '\0';						/* Is now */

	if (strcmp(buf, byteorder))
		CROAK(("Byte order is not compatible"));
	
	GETMARK(c);		/* sizeof(int) */
	if ((int) c != sizeof(int))
		CROAK(("Integer size is not compatible"));

	GETMARK(c);		/* sizeof(long) */
	if ((int) c != sizeof(long))
		CROAK(("Long integer size is not compatible"));

	GETMARK(c);		/* sizeof(char *) */
	if ((int) c != sizeof(char *))
		CROAK(("Pointer integer size is not compatible"));

	return &PL_sv_undef;	/* OK */
}

/*
 * retrieve
 *
 * Recursively retrieve objects from the specified file and return their
 * root SV (which may be an AV or an HV for what we care).
 * Returns null if there is a problem.
 */
static SV *retrieve(cxt)
stcxt_t *cxt;
{
	int type;
	SV **svh;
	SV *sv;

	TRACEME(("retrieve"));

	/*
	 * Grab address tag which identifies the object if we are retrieving
	 * an older format. Since the new binary format counts objects and no
	 * longer explicitely tags them, we must keep track of the correspondance
	 * ourselves.
	 *
	 * The following section will disappear one day when the old format is
	 * no longer supported, hence the final "goto" in the "if" block.
	 */

	if (cxt->hseen) {						/* Retrieving old binary */
		stag_t tag;
		if (cxt->netorder) {
			I32 nettag;
			READ(&nettag, sizeof(I32));		/* Ordered sequence of I32 */
			tag = (stag_t) nettag;
		} else
			READ(&tag, sizeof(stag_t));		/* Original address of the SV */

		GETMARK(type);
		if (type == SX_OBJECT) {
			I32 tagn;
			svh = hv_fetch(cxt->hseen, (char *) &tag, sizeof(tag), FALSE);
			if (!svh)
				CROAK(("Old tag 0x%x should have been mapped already", tag));
			tagn = SvIV(*svh);	/* Mapped tag number computed earlier below */

			/*
			 * The following code is common with the SX_OBJECT case below.
			 */

			svh = av_fetch(cxt->aseen, tagn, FALSE);
			if (!svh)
				CROAK(("Object #%d should have been retrieved already", tagn));
			sv = *svh;
			TRACEME(("has retrieved #%d at 0x%lx", tagn, (unsigned long) sv));
			SvREFCNT_inc(sv);	/* One more reference to this same sv */
			return sv;			/* The SV pointer where object was retrieved */
		}

		/*
		 * Map new object, but don't increase tagnum. This will be done
		 * by each of the retrieve_* functions when they call SEEN().
		 *
		 * The mapping associates the "tag" initially present with a unique
		 * tag number. See test for SX_OBJECT above to see how this is perused.
		 */

		if (!hv_store(cxt->hseen, (char *) &tag, sizeof(tag),
				newSViv(cxt->tagnum), 0))
			return (SV *) 0;

		goto first_time;
	}

	/*
	 * Regular post-0.6 binary format.
	 */

again:
	GETMARK(type);

	TRACEME(("retrieve type = %d", type));

	/*
	 * Are we dealing with an object we should have already retrieved?
	 */

	if (type == SX_OBJECT) {
		I32 tag;
		READ(&tag, sizeof(I32));
		tag = ntohl(tag);
		svh = av_fetch(cxt->aseen, tag, FALSE);
		if (!svh)
			CROAK(("Object #%d should have been retrieved already", tag));
		sv = *svh;
		TRACEME(("had retrieved #%d at 0x%lx", tag, (unsigned long) sv));
		SvREFCNT_inc(sv);	/* One more reference to this same sv */
		return sv;			/* The SV pointer where object was retrieved */
	}

first_time:		/* Will disappear when support for old format is dropped */

	/*
	 * Okay, first time through for this one.
	 */

	sv = RETRIEVE(cxt, type)(cxt);
	if (!sv)
		return (SV *) 0;			/* Failed */

	/*
	 * Old binary formats (pre-0.7).
	 *
	 * Final notifications, ended by SX_STORED may now follow.
	 * Currently, the only pertinent notification to apply on the
	 * freshly retrieved object is either:
	 *    SX_CLASS <char-len> <classname> for short classnames.
	 *    SX_LG_CLASS <int-len> <classname> for larger one (rare!).
	 * Class name is then read into the key buffer pool used by
	 * hash table key retrieval.
	 */

	if (cxt->ver_major < 2) {
		while ((type = GETCHAR()) != SX_STORED) {
			I32 len;
			switch (type) {
			case SX_CLASS:
				GETMARK(len);			/* Length coded on a single char */
				break;
			case SX_LG_CLASS:			/* Length coded on a regular integer */
				RLEN(len);
				break;
			case EOF:
			default:
				return (SV *) 0;		/* Failed */
			}
			KBUFCHK(len);				/* Grow buffer as necessary */
			if (len)
				READ(kbuf, len);
			kbuf[len] = '\0';			/* Mark string end */
			BLESS(sv, kbuf);
		}
	}

	TRACEME(("ok (retrieved 0x%lx, refcnt=%d, %s)", (unsigned long) sv,
		SvREFCNT(sv) - 1, sv_reftype(sv, FALSE)));

	return sv;	/* Ok */
}

/*
 * do_retrieve
 *
 * Retrieve data held in file and return the root object.
 * Common routine for pretrieve and mretrieve.
 */
static SV *do_retrieve(f, in, optype)
PerlIO *f;
SV *in;
int optype;
{
	dSTCXT;
	SV *sv;
	struct extendable msave;	/* Where potentially valid mbuf is saved */

	TRACEME(("do_retrieve (optype = 0x%x)", optype));

	optype |= ST_RETRIEVE;

	/*
	 * Sanity assertions for retrieve dispatch tables.
	 */

	ASSERT(sizeof(sv_old_retrieve) == sizeof(sv_retrieve),
		("old and new retrieve dispatch table have same size"));
	ASSERT(sv_old_retrieve[SX_ERROR] == retrieve_other,
		("SX_ERROR entry correctly initialized in old dispatch table"));
	ASSERT(sv_retrieve[SX_ERROR] == retrieve_other,
		("SX_ERROR entry correctly initialized in new dispatch table"));

	/*
	 * Workaround for CROAK leak: if they enter with a "dirty" context,
	 * free up memory for them now.
	 */

	if (cxt->dirty)
		clean_context(cxt);

	/*
	 * Now that STORABLE_xxx hooks exist, it is possible that they try to
	 * re-enter retrieve() via the hooks.
	 */

	if (cxt->entry)
		cxt = allocate_context(cxt);

	cxt->entry++;

	ASSERT(cxt->entry == 1, ("starting new recursion"));
	ASSERT(!cxt->dirty, ("clean context"));

	/*
	 * Prepare context.
	 *
	 * Data is loaded into the memory buffer when f is NULL, unless `in' is
	 * also NULL, in which case we're expecting the data to already lie
	 * in the buffer (dclone case).
	 */

	KBUFINIT();			 		/* Allocate hash key reading pool once */

	if (!f && in) {
		StructCopy(&cxt->membuf, &msave, struct extendable);
		MBUF_LOAD(in);
	}


	/*
	 * Magic number verifications.
	 *
	 * This needs to be done before calling init_retrieve_context()
	 * since the format indication in the file are necessary to conduct
	 * some of the initializations.
	 */

	cxt->fio = f;				/* Where I/O are performed */

	if (!magic_check(cxt))
		CROAK(("Magic number checking on storable %s failed",
			cxt->fio ? "file" : "string"));

	TRACEME(("data stored in %s format",
		cxt->netorder ? "net order" : "native"));

	init_retrieve_context(cxt, optype);

	ASSERT(is_retrieving(), ("within retrieve operation"));

	sv = retrieve(cxt);		/* Recursively retrieve object, get root SV */

	/*
	 * Final cleanup.
	 */

	if (!f && in)
		StructCopy(&msave, &cxt->membuf, struct extendable);

	/*
	 * The "root" context is never freed.
	 */

	clean_retrieve_context(cxt);
	if (cxt->prev)				/* This context was stacked */
		free_context(cxt);		/* It was not the "root" context */

	/*
	 * Prepare returned value.
	 */

	if (!sv) {
		TRACEME(("retrieve ERROR"));
		return &PL_sv_undef;		/* Something went wrong, return undef */
	}

	TRACEME(("retrieve got %s(0x%lx)",
		sv_reftype(sv, FALSE), (unsigned long) sv));

	/*
	 * Backward compatibility with Storable-0.5@9 (which we know we
	 * are retrieving if hseen is non-null): don't create an extra RV
	 * for objects since we special-cased it at store time.
	 *
	 * Build a reference to the SV returned by pretrieve even if it is
	 * already one and not a scalar, for consistency reasons.
	 *
	 * NB: although context might have been cleaned, the value of `cxt->hseen'
	 * remains intact, and can be used as a flag.
	 */

	if (cxt->hseen) {			/* Was not handling overloading by then */
		SV *rv;
		if (sv_type(sv) == svis_REF && (rv = SvRV(sv)) && SvOBJECT(rv))
			return sv;
	}

	/*
	 * If reference is overloaded, restore behaviour.
	 *
	 * NB: minor glitch here: normally, overloaded refs are stored specially