/* This file is part of the Variable::Magic Perl module.
 * See http://search.cpan.org/dist/Variable-Magic/ */

#include <stdio.h>  /* sprintf() */

#define PERL_NO_GET_CONTEXT
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

#define __PACKAGE__ "Variable::Magic"

#define R(S) fprintf(stderr, "R(" #S ") = %d\n", SvREFCNT(S))

#define PERL_VERSION_LE(R, V, S) (PERL_REVISION < (R) || (PERL_REVISION == (R) && (PERL_VERSION < (V) || (PERL_VERSION == (V) && (PERL_SUBVERSION <= (S))))))

#define PERL_API_VERSION_GE(R, V, S) (PERL_API_REVISION > (R) || (PERL_API_REVISION == (R) && (PERL_API_VERSION > (V) || (PERL_API_VERSION == (V) && (PERL_API_SUBVERSION >= (S))))))

/* --- Compatibility ------------------------------------------------------- */

#ifndef Newx
# define Newx(v, n, c) New(0, v, n, c)
#endif

#ifndef SvMAGIC_set
# define SvMAGIC_set(sv, val) (SvMAGIC(sv) = (val))
#endif

#ifndef dMY_CXT
# define MY_CXT vmg_globaldata
# define dMY_CXT
# define START_MY_CXT STATIC my_cxt_t MY_CXT;
# define MY_CXT_INIT
#endif

#ifndef PERL_MAGIC_ext
# define PERL_MAGIC_ext '~'
#endif

#ifndef MGf_COPY
# define MGf_COPY 0
#endif /* !MGf_COPY */

#ifndef MGf_DUP
# define MGf_DUP 0
#endif /* !MGf_DUP */

#ifndef MGf_LOCAL
# define MGf_LOCAL 0
#endif /* !MGf_LOCAL */

/* --- Context-safe global data -------------------------------------------- */

#define MY_CXT_KEY __PACKAGE__ "::_guts" XS_VERSION

typedef struct {
 HV *wizz;
 U16 count;
} my_cxt_t;

START_MY_CXT

/* --- Signatures ---------------------------------------------------------- */

#define SIG_MIN ((U16) (1u << 8))
#define SIG_MAX ((U16) (1u << 16 - 1))
#define SIG_NBR (SIG_MAX - SIG_MIN + 1)
#define SIG_WIZ ((U16) (1u << 8 - 1))

/* ... Generate signatures ................................................. */

STATIC U16 vmg_gensig(pTHX) {
#define vmg_gensig() vmg_gensig(aTHX)
 U16 sig;
 char buf[8];
 dMY_CXT;

 do {
  sig = SIG_NBR * Drand01() + SIG_MIN;
 } while (hv_exists(MY_CXT.wizz, buf, sprintf(buf, "%u", sig)));

 return sig;
}

/* --- MGWIZ structure ----------------------------------------------------- */

typedef struct {
 MGVTBL *vtbl;
 U16 sig;
 int uvar;
 SV *cb_data;
 SV *cb_get, *cb_set, *cb_len, *cb_clear, *cb_free;
#if MGf_COPY
 SV *cb_copy;
#endif /* MGf_COPY */
#if MGf_DUP
 SV *cb_dup;
#endif /* MGf_DUP */
#if MGf_LOCAL
 SV *cb_local;
#endif /* MGf_LOCAL */
 SV *cb_fetch, *cb_store, *cb_exists, *cb_delete;
} MGWIZ;

#define MGWIZ2SV(W) (newSVuv(PTR2UV(W)))
#define SV2MGWIZ(S) (INT2PTR(MGWIZ*, SvUVX((SV *) (S))))

/* ... Construct private data .............................................. */

STATIC SV *vmg_data_new(pTHX_ SV *ctor, SV *sv, AV *args) {
#define vmg_data_new(C, S, A) vmg_data_new(aTHX_ (C), (S), (A))
 SV *nsv;

 dSP;
 int count;

 ENTER;
 SAVETMPS;

 PUSHMARK(SP);
 XPUSHs(sv_2mortal(newRV_inc(sv)));
 if (args != NULL) {
  I32 i, alen = av_len(args);
  for (i = 0; i < alen; ++i) { XPUSHs(*av_fetch(args, i, 0)); }
 }
 PUTBACK;

 count = call_sv(ctor, G_SCALAR);

 SPAGAIN;

 if (count != 1) { croak("Callback needs to return 1 scalar\n"); }
 nsv = POPs;
#if PERL_VERSION_LE(5, 8, 2)
 nsv = sv_newref(nsv); /* Workaround some bug in SvREFCNT_inc() */
#else
 SvREFCNT_inc(nsv);    /* Or it will be destroyed in FREETMPS */
#endif

 PUTBACK;

 FREETMPS;
 LEAVE;

 return nsv;
}

STATIC SV *vmg_data_get(SV *sv, U16 sig) {
 MAGIC *mg, *moremagic;
 MGWIZ *w;

 if (SvTYPE(sv) >= SVt_PVMG) {
  for (mg = SvMAGIC(sv); mg; mg = moremagic) {
   moremagic = mg->mg_moremagic;
   if ((mg->mg_type == PERL_MAGIC_ext) && (mg->mg_private == sig)) { break; }
  }
  if (mg) { return mg->mg_obj; }
 }

 return NULL;
} 

/* ... Magic cast/dispell .................................................. */

STATIC I32 vmg_uf_val(pTHX_ IV idx, SV *sv);

STATIC UV vmg_cast(pTHX_ SV *sv, SV *wiz, AV *args) {
#define vmg_cast(S, W, A) vmg_cast(aTHX_ (S), (W), (A))
 int has_uvar = 0;
 MAGIC *mg = NULL, *moremagic = NULL;
 MGWIZ *w;
 SV *data;

 w = SV2MGWIZ(wiz);

 if ((SvTYPE(sv) >= SVt_PVMG) && (mg = SvMAGIC(sv))) {
  if (mg->mg_type == PERL_MAGIC_uvar) { has_uvar = 1; }
  do {
   if ((mg->mg_type == PERL_MAGIC_ext) && (mg->mg_private == w->sig)) { break;}
   mg = mg->mg_moremagic;
  } while (mg);
  if (mg) { return 1; }
 }

 if (w->uvar && (SvTYPE(sv) >= SVt_PVHV) && !has_uvar) {
  struct ufuncs uf;
  uf.uf_val   = vmg_uf_val;
  uf.uf_set   = NULL;
  uf.uf_index = 0;
  sv_magicext(sv, NULL, PERL_MAGIC_uvar, &PL_vtbl_uvar, (char *) &uf, sizeof(uf));
 }

 data = (w->cb_data) ? vmg_data_new(w->cb_data, sv, args) : NULL;
 mg = sv_magicext(sv, data, PERL_MAGIC_ext, w->vtbl, (char *) wiz, HEf_SVKEY);
 mg->mg_private = w->sig;
 mg->mg_flags   = mg->mg_flags
#if MGf_COPY
                | MGf_COPY
#endif /* MGf_COPY */
#if MGf_DUP
                | MGf_DUP
#endif /* MGf_DUP */
#if MGf_LOCAL
                | MGf_LOCAL
#endif /* MGf_LOCAL */
 ;

 return 1;
}

STATIC UV vmg_dispell(pTHX_ SV *sv, U16 sig) {
#define vmg_dispell(S, Z) vmg_dispell(aTHX_ (S), (Z))
 MAGIC *mg, *prevmagic, *moremagic = NULL;
 MGWIZ *w;

 if (SvTYPE(sv) < SVt_PVMG) { return 0; }

 for (prevmagic = NULL, mg = SvMAGIC(sv); mg; prevmagic = mg, mg = moremagic) {
  moremagic = mg->mg_moremagic;
  if ((mg->mg_type == PERL_MAGIC_ext) && (mg->mg_private == sig)) { break; }
 }
 if (!mg) { return 0; }

 if (prevmagic) {
  prevmagic->mg_moremagic = moremagic;
 } else {
  SvMAGIC_set(sv, moremagic);
 }
 mg->mg_moremagic = NULL;

 if (mg->mg_obj != sv) { SvREFCNT_dec(mg->mg_obj); } /* Destroy private data */
 SvREFCNT_dec((SV *) mg->mg_ptr); /* Unreference the wizard */
 Safefree(mg);

 return 1;
}

/* ... svt callbacks ....................................................... */

STATIC int vmg_cb_call(pTHX_ SV *cb, SV *sv, SV *data) {
#define vmg_cb_call(I, S, D) vmg_cb_call(aTHX_ (I), (S), (D))
 int ret;

 dSP;
 int count;

 ENTER;
 SAVETMPS;

 PUSHMARK(SP);
 XPUSHs(sv_2mortal(newRV_inc(sv)));
 if (data) { XPUSHs(data); }
 PUTBACK;

 count = call_sv(cb, G_SCALAR);

 SPAGAIN;

 if (count != 1) { croak("Callback needs to return 1 scalar\n"); }
 ret = POPi;

 PUTBACK;

 FREETMPS;
 LEAVE;

 return ret;
}

STATIC int vmg_cb_call2(pTHX_ SV *cb, SV *sv, SV *data, SV *extra) {
#define vmg_cb_call2(I, S, D, E) vmg_cb_call2(aTHX_ (I), (S), (D), (E))
 int ret;

 dSP;
 int count;

 ENTER;
 SAVETMPS;

 PUSHMARK(SP);
 XPUSHs(sv_2mortal(newRV_inc(sv)));
 XPUSHs(data ? data : &PL_sv_undef);
 if (extra) { XPUSHs(extra); }
 PUTBACK;

 count = call_sv(cb, G_SCALAR);

 SPAGAIN;

 if (count != 1) { croak("Callback needs to return 1 scalar\n"); }
 ret = POPi;

 PUTBACK;

 FREETMPS;
 LEAVE;

 return ret;
}

STATIC int vmg_svt_get(pTHX_ SV *sv, MAGIC *mg) {
 return vmg_cb_call(SV2MGWIZ(mg->mg_ptr)->cb_get, sv, mg->mg_obj);
}

STATIC int vmg_svt_set(pTHX_ SV *sv, MAGIC *mg) {
 return vmg_cb_call(SV2MGWIZ(mg->mg_ptr)->cb_set, sv, mg->mg_obj);
}

STATIC U32 vmg_svt_len(pTHX_ SV *sv, MAGIC *mg) {
 U32 ret;

 dSP;
 int count;

 ENTER;
 SAVETMPS;

 PUSHMARK(SP);
 XPUSHs(sv_2mortal(newRV_inc(sv)));
 XPUSHs((mg->mg_obj) ? (mg->mg_obj) : &PL_sv_undef);
 if (SvTYPE(sv) == SVt_PVAV) {
  XPUSHs(sv_2mortal(newSViv(av_len((AV *) sv) + 1)));
 }
 PUTBACK;

 count = call_sv(SV2MGWIZ(mg->mg_ptr)->cb_len, G_SCALAR);

 SPAGAIN;

 if (count != 1) { croak("Callback needs to return 1 scalar\n"); }
 ret = POPi;

 PUTBACK;

 FREETMPS;
 LEAVE;

 return ret - 1;
}

STATIC int vmg_svt_clear(pTHX_ SV *sv, MAGIC *mg) {
 return vmg_cb_call(SV2MGWIZ(mg->mg_ptr)->cb_clear, sv, mg->mg_obj);
}

STATIC int vmg_svt_free(pTHX_ SV *sv, MAGIC *mg) {
 /* So that it can survive tmp cleanup in vmg_cb_call */
 SvREFCNT_inc(sv);
 /* Perl_mg_free will get rid of the magic and decrement mg->mg_obj and
  * mg->mg_ptr reference count */
 return vmg_cb_call(SV2MGWIZ(mg->mg_ptr)->cb_free, sv, mg->mg_obj);
}

#if MGf_COPY
STATIC int vmg_svt_copy(pTHX_ SV *sv, MAGIC *mg, SV *nsv, const char *name, int namelen) {
 return vmg_cb_call2(SV2MGWIZ(mg->mg_ptr)->cb_copy, sv, mg->mg_obj, nsv);
}
#endif /* MGf_COPY */

#if MGf_DUP
STATIC int vmg_svt_dup(pTHX_ MAGIC *mg, CLONE_PARAMS *p) {
 return 0;
}
#endif /* MGf_DUP */

#if MGf_LOCAL
STATIC int vmg_svt_local(pTHX_ SV *nsv, MAGIC *mg) {
 return vmg_cb_call(SV2MGWIZ(mg->mg_ptr)->cb_local, nsv, mg->mg_obj);
}
#endif /* MGf_LOCAL */

STATIC I32 vmg_uf_val(pTHX_ IV idx, SV *sv) {
 MAGIC *mg;
 SV *key;
 for (mg = SvMAGIC(sv); mg; mg = mg->mg_moremagic) {
  if (mg->mg_type == PERL_MAGIC_uvar) { key = mg->mg_obj; break; }
 }
 if (!key) { return 0; }
 for (mg = SvMAGIC(sv); mg; mg = mg->mg_moremagic) {
  MGWIZ *w;
  if ((mg->mg_type != PERL_MAGIC_ext) ||
      (mg->mg_private < SIG_MIN) || (mg->mg_private > SIG_MAX)) { continue; }
  w = SV2MGWIZ(mg->mg_ptr);
  if (!w->uvar) { continue; }
  switch (idx & (HV_FETCH_ISSTORE|HV_FETCH_ISEXISTS|HV_FETCH_LVALUE|HV_DELETE)){
   case 0:
    if (w->cb_fetch) { return vmg_cb_call2(w->cb_fetch, sv, mg->mg_obj, key); }
    break;
   case HV_FETCH_ISSTORE:
   case HV_FETCH_LVALUE:
   case (HV_FETCH_ISSTORE|HV_FETCH_LVALUE):
    if (w->cb_store) { return vmg_cb_call2(w->cb_store, sv, mg->mg_obj, key); }
    break;
   case HV_FETCH_ISEXISTS:
    if (w->cb_exists) { return vmg_cb_call2(w->cb_exists, sv, mg->mg_obj, key);}
    break;
   case HV_DELETE:
    if (w->cb_delete) { return vmg_cb_call2(w->cb_delete, sv, mg->mg_obj, key);}
    break;
  }
 }
 return 0;
}

/* ... Wizard destructor ................................................... */

STATIC int vmg_wizard_free(pTHX_ SV *wiz, MAGIC *mg) {
 char buf[8];
 MGWIZ *w;
 dMY_CXT;

 w = SV2MGWIZ(wiz);

 SvREFCNT_inc(wiz); /* Fake survival - it's gonna be deleted anyway */
#if PERL_API_VERSION_GE(5, 9, 5)
 SvREFCNT_inc(wiz); /* One more push */
#endif
 if (hv_delete(MY_CXT.wizz, buf, sprintf(buf, "%u", w->sig), 0)) {
  --MY_CXT.count;
 }

 if (w->cb_data  != NULL) { SvREFCNT_dec(SvRV(w->cb_data)); }
 if (w->cb_get   != NULL) { SvREFCNT_dec(SvRV(w->cb_get)); }
 if (w->cb_set   != NULL) { SvREFCNT_dec(SvRV(w->cb_set)); }
 if (w->cb_len   != NULL) { SvREFCNT_dec(SvRV(w->cb_len)); }
 if (w->cb_clear != NULL) { SvREFCNT_dec(SvRV(w->cb_clear)); }
 if (w->cb_free  != NULL) { SvREFCNT_dec(SvRV(w->cb_free)); }
#if MGf_COPY
 if (w->cb_copy  != NULL) { SvREFCNT_dec(SvRV(w->cb_copy)); }
#endif /* MGf_COPY */
#if MGf_DUP
 if (w->cb_dup   != NULL) { SvREFCNT_dec(SvRV(w->cb_dup)); }
#endif /* MGf_DUP */
#if MGf_LOCAL
 if (w->cb_local != NULL) { SvREFCNT_dec(SvRV(w->cb_local)); }
#endif /* MGf_LOCAL */
 if (w->cb_fetch != NULL) { SvREFCNT_dec(SvRV(w->cb_fetch)); }
 if (w->cb_store != NULL) { SvREFCNT_dec(SvRV(w->cb_store)); }
 if (w->cb_exists != NULL) { SvREFCNT_dec(SvRV(w->cb_exists)); }
 if (w->cb_delete != NULL) { SvREFCNT_dec(SvRV(w->cb_delete)); }
 Safefree(w->vtbl);
 Safefree(w);

 return 0;
}

STATIC MGVTBL vmg_wizard_vtbl = {
 NULL,            /* get */
 NULL,            /* set */
 NULL,            /* len */
 NULL,            /* clear */
 vmg_wizard_free, /* free */
#if MGf_COPY
 NULL,            /* copy */
#endif /* MGf_COPY */
#if MGf_DUP
 NULL,            /* dup */
#endif /* MGf_DUP */
#if MGf_LOCAL
 NULL,            /* local */
#endif /* MGf_LOCAL */
};

/* --- Error messages and misc helpers ------------------------------------- */

STATIC const char vmg__wizard_args[]   = "_wizard() called with a wrong number of arguments - use wizard() instead";
STATIC const char vmg_invalid_wiz[]    = "Invalid wizard object";
STATIC const char vmg_invalid_sv[]     = "Invalid variable";
STATIC const char vmg_invalid_sig[]    = "Invalid numeric signature";
STATIC const char vmg_toomanysigs[]    = "Too many magic signatures used";
STATIC const char vmg_argstorefailed[] = "Error while storing arguments";

STATIC U16 vmg_sv2sig(pTHX_ SV *sv) {
#define vmg_sv2sig(S) vmg_sv2sig(aTHX_ (S))
 U16 sig;

 if (SvIOK(sv)) {
  sig = SvUVX(sv);
 } else if (SvNOK(sv)) {
  sig = SvNVX(sv);
 } else if ((SvPOK(sv) && grok_number(SvPVX(sv), SvCUR(sv), NULL))) {
  sig = SvUV(sv);
 } else {
  croak(vmg_invalid_sig);
 }
 if (sig < SIG_MIN) { sig += SIG_MIN; }
 if (sig > SIG_MAX) { sig %= SIG_MAX + 1; }

 return sig;
}

#define VMG_SET_CB(T, M, CB) \
 cb = (CB); \
 (M)->cb_##T = (SvROK(cb)) ? newRV_inc(SvRV(cb)) : NULL;

#define VMG_SET_CB_SVT(T, V, M, CB) \
 cb = (CB); \
 if (SvROK(cb)) { \
  (V)->svt_##T = vmg_svt_##T; (M)->cb_##T = newRV_inc(SvRV(cb)); \
 } else { \
  (V)->svt_##T = NULL;        (M)->cb_##T = NULL; \
 }

/* --- XS ------------------------------------------------------------------ */

MODULE = Variable::Magic            PACKAGE = Variable::Magic

PROTOTYPES: ENABLE

BOOT:
{
 HV *stash;
 MY_CXT_INIT;
 MY_CXT.wizz = newHV();
 MY_CXT.count = 0;
 stash = gv_stashpv(__PACKAGE__, 1);
 newCONSTSUB(stash, "SIG_MIN",   newSVuv(SIG_MIN));
 newCONSTSUB(stash, "SIG_MAX",   newSVuv(SIG_MAX));
 newCONSTSUB(stash, "SIG_NBR",   newSVuv(SIG_NBR));
 newCONSTSUB(stash, "MGf_COPY",  newSVuv(MGf_COPY));
 newCONSTSUB(stash, "MGf_DUP",   newSVuv(MGf_DUP));
 newCONSTSUB(stash, "MGf_LOCAL", newSVuv(MGf_LOCAL));
}

SV *_wizard(SV *svsig, ...)
PROTOTYPE: $@
PREINIT:
 U16 sig;
 I32 i;
 char buf[8];
 MGWIZ *w;
 MGVTBL *t;
 MAGIC *mg;
 SV *cb, *sv;
CODE:
 dMY_CXT;

 if (items != 14) { croak(vmg__wizard_args); }

 if (SvOK(svsig)) {
  SV **old;
  sig = vmg_sv2sig(svsig);
  if (old = hv_fetch(MY_CXT.wizz, buf, sprintf(buf, "%u", sig), 0)) {
   ST(0) = sv_2mortal(newRV_inc(*old));
   XSRETURN(1);
  }
 } else {
  if (MY_CXT.count >= SIG_NBR) { croak(vmg_toomanysigs); }
  sig = vmg_gensig();
 }

 Newx(t, 1, MGVTBL);
 Newx(w, 1, MGWIZ);
 w->vtbl = t;
 w->sig  = sig;

 VMG_SET_CB(data,         w, ST(1));
 VMG_SET_CB_SVT(get,   t, w, ST(2));
 VMG_SET_CB_SVT(set,   t, w, ST(3));
 VMG_SET_CB_SVT(len,   t, w, ST(4));
 VMG_SET_CB_SVT(clear, t, w, ST(5));
 VMG_SET_CB_SVT(free,  t, w, ST(6));
#if MGf_COPY
 VMG_SET_CB_SVT(copy,  t, w, ST(7));
#endif /* MGf_COPY */
#if MGf_DUP
 VMG_SET_CB_SVT(dup,   t, w, ST(8));
#endif /* MGf_DUP */
#if MGf_LOCAL
 VMG_SET_CB_SVT(local, t, w, ST(9));
#endif /* MGf_LOCAL */
 VMG_SET_CB(fetch,        w, ST(10));
 VMG_SET_CB(store,        w, ST(11));
 VMG_SET_CB(exists,       w, ST(12));
 VMG_SET_CB(delete,       w, ST(13));

 w->uvar = (w->cb_fetch || w->cb_store || w->cb_exists || w->cb_delete);

 sv = MGWIZ2SV(w);
 mg = sv_magicext(sv, NULL, PERL_MAGIC_ext, &vmg_wizard_vtbl, NULL, -1);
 mg->mg_private = SIG_WIZ;
#if MGf_COPY
 if (t->svt_copy)  { mg->mg_flags |= MGf_COPY; }
#endif /* MGf_COPY */
#if MGf_DUP
 if (t->svt_dup)   { mg->mg_flags |= MGf_DUP; }
#endif /* MGf_DUP */
#if MGf_LOCAL
 if (t->svt_local) { mg->mg_flags |= MGf_LOCAL; }
#endif /* MGf_LOCAL */

 hv_store(MY_CXT.wizz, buf, sprintf(buf, "%u", sig), sv, 0);
 ++MY_CXT.count;
 
 RETVAL = newRV_noinc(sv);
OUTPUT:
 RETVAL

SV *gensig()
PROTOTYPE:
CODE:
 dMY_CXT;
 if (MY_CXT.count >= SIG_NBR) { croak(vmg_toomanysigs); }
 RETVAL = newSVuv(vmg_gensig());
OUTPUT:
 RETVAL

SV *getsig(SV *wiz)
PROTOTYPE: $
CODE:
 if (!SvROK(wiz)) { croak(vmg_invalid_wiz); }
 RETVAL = newSVuv(SV2MGWIZ(SvRV(wiz))->sig);
OUTPUT:
 RETVAL

SV *cast(SV *sv, SV *wiz, ...)
PROTOTYPE: \[$@%&*]$@
PREINIT:
 AV *args = NULL;
 SV *ret;
CODE:
 dMY_CXT;
 if (SvROK(wiz)) {
  wiz = SvRV(wiz);
 } else if (SvOK(wiz)) {
  char buf[8];
  SV **old;
  U16 sig = vmg_sv2sig(wiz);
  if (old = hv_fetch(MY_CXT.wizz, buf, sprintf(buf, "%u", sig), 0)) {
   wiz = *old;
  } else {
   XSRETURN_UNDEF;
  }
 } else {
  croak(vmg_invalid_sig);
 }
 if (items > 2) {
  I32 i;
  args = newAV();
  av_fill(args, items - 2);
  for (i = 2; i < items; ++i) {
   SV *arg = ST(i);
   SvREFCNT_inc(arg);
   if (av_store(args, i - 2, arg) == NULL) { croak(vmg_argstorefailed); }
  }
 }
 ret = newSVuv(vmg_cast(SvRV(sv), wiz, args));
 SvREFCNT_dec(args);
 RETVAL = ret;
OUTPUT:
 RETVAL

SV *getdata(SV *sv, SV *wiz)
PROTOTYPE: \[$@%&*]$
PREINIT:
 SV *data;
 U16 sig;
CODE:
 dMY_CXT;
 if (SvROK(wiz)) {
  sig = SV2MGWIZ(SvRV(wiz))->sig;
 } else if (SvOK(wiz)) {
  char buf[8];
  sig = vmg_sv2sig(wiz);
  if (!hv_fetch(MY_CXT.wizz, buf, sprintf(buf, "%u", sig), 0)) {
   XSRETURN_UNDEF;
  }
 } else {
  croak(vmg_invalid_wiz);
 }
 data = vmg_data_get(SvRV(sv), sig);
 if (!data) { XSRETURN_UNDEF; }
 ST(0) = newSVsv(data);
 XSRETURN(1);

SV *dispell(SV *sv, SV *wiz)
PROTOTYPE: \[$@%&*]$
PREINIT:
 U16 sig;
CODE:
 dMY_CXT;
 if (SvROK(wiz)) {
  sig = SV2MGWIZ(SvRV(wiz))->sig;
 } else if (SvOK(wiz)) {
  char buf[8];
  sig = vmg_sv2sig(wiz);
  if (!hv_fetch(MY_CXT.wizz, buf, sprintf(buf, "%u", sig), 0)) {
   XSRETURN_UNDEF;
  }
 } else {
  croak(vmg_invalid_wiz);
 }
 RETVAL = newSVuv(vmg_dispell(SvRV(sv), sig));
OUTPUT:
 RETVAL