C++ savestack函数代码示例

static void GCTM (lua_State *L, int propagateerrors) {
  global_State *g = G(L);
  const TValue *tm;
  TValue v;
  setgcovalue(L, &v, udata2finalize(g));
  tm = luaT_gettmbyobj(L, &v, TM_GC);
  if (tm != NULL && ttisfunction(tm)) {  /* is there a finalizer? */
    int status;
    lu_byte oldah = L->allowhook;
    int running  = g->gcrunning;
    L->allowhook = 0;  /* stop debug hooks during GC metamethod */
    g->gcrunning = 0;  /* avoid GC steps */
    setobj2s(L, L->top, tm);  /* push finalizer... */
    setobj2s(L, L->top + 1, &v);  /* ... and its argument */
    L->top += 2;  /* and (next line) call the finalizer */
    status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
    L->allowhook = oldah;  /* restore hooks */
    g->gcrunning = running;  /* restore state */
    if (status != LUA_OK && propagateerrors) {  /* error while running __gc? */
      if (status == LUA_ERRRUN) {  /* is there an error object? */
        const char *msg = (ttisstring(L->top - 1))
                            ? svalue(L->top - 1)
                            : "no message";
        luaO_pushfstring(L, "error in __gc metamethod (%s)", msg);
        status = LUA_ERRGCMM;  /* error in __gc metamethod */
      }
      luaD_throw(L, status);  /* re-throw error */
    }
  }
}

static void Arith (lua_State *L, StkId ra,
                   const TObject *rb, const TObject *rc, TMS op) {
  TObject tempb, tempc;
  const TObject *b, *c;
  if ((b = luaV_tonumber(rb, &tempb)) != NULL &&
      (c = luaV_tonumber(rc, &tempc)) != NULL) {
    switch (op) {
      case TM_ADD: setnvalue(ra, nvalue(b) + nvalue(c)); break;
      case TM_SUB: setnvalue(ra, nvalue(b) - nvalue(c)); break;
      case TM_MUL: setnvalue(ra, nvalue(b) * nvalue(c)); break;
      case TM_DIV: setnvalue(ra, nvalue(b) / nvalue(c)); break;
      case TM_POW: {
        const TObject *f = luaH_getstr(hvalue(gt(L)), G(L)->tmname[TM_POW]);
        ptrdiff_t res = savestack(L, ra);
        if (!ttisfunction(f))
          luaG_runerror(L, "`__pow' (`^' operator) is not a function");
        callTMres(L, f, b, c);
        ra = restorestack(L, res);  /* previous call may change stack */
        setobjs2s(ra, L->top);
        break;
      }
      default: lua_assert(0); break;
    }
  }
  else if (!call_binTM(L, rb, rc, ra, op))
    luaG_aritherror(L, rb, rc);
}

/*
** If function yielded, its 'func' can be in the 'extra' field. The
** next function restores 'func' to its correct value for debugging
** purposes. (It exchanges 'func' and 'extra'; so, when called again,
** after debugging, it also "re-restores" ** 'func' to its altered value.
*/
static void swapextra (lua_State *L) {
  if (L->status == LUA_YIELD) {
    CallInfo *ci = L->ci;  /* get function that yielded */
    StkId temp = ci->func;  /* exchange its 'func' and 'extra' values */
    ci->func = restorestack(L, ci->extra);
    ci->extra = savestack(L, temp);
  }
}

static void Arith (lua_State *L, StkId ra, const TValue *rb,
                   const TValue *rc, TMS op)
{
	TValue tempb, tempc;
	const TValue *b, *c;
	if ((b = luaV_tonumber(rb, &tempb)) != NULL &&
	    (c = luaV_tonumber(rc, &tempc)) != NULL) {
		lua_Number nb = nvalue(b), nc = nvalue(c);
		switch (op) {
		case TM_ADD:
			setnvalue(ra, luai_numadd(nb, nc));
			break;
		case TM_SUB:
			setnvalue(ra, luai_numsub(nb, nc));
			break;
		case TM_MUL:
			setnvalue(ra, luai_nummul(nb, nc));
			break;
		case TM_DIV:
			setnvalue(ra, luai_lnumdiv(nb, nc));
			break;
		case TM_MOD:
			setnvalue(ra, luai_lnummod(nb, nc));
			break;
		case TM_POW:
			setnvalue(ra, luai_numpow(nb, nc));
			break;
		case TM_UNM:
			setnvalue(ra, luai_numunm(nb));
			break;
		default:
			lua_assert(0);
			break;
		}
	} else {
		ptrdiff_t br = savestack(L, rb);
		ptrdiff_t cr = savestack(L, rc);
		if (!call_binTM(L, rb, rc, ra, op)) {
			luaG_aritherror(L, restorestack(L, br), restorestack(L, cr));
		}
	}
}

void luaD_seterrorobj (lua_State *L, int errcode, StkId oldtop) {
  switch (errcode) {
    case LUA_ERRMEM: {
      ptrdiff_t oldtopr = savestack(L, oldtop);
      setsvalue2s(L, restorestack(L, oldtopr), luaS_newliteral(L, MEMERRMSG));
      break;
    }
    case LUA_ERRERR: {
      ptrdiff_t oldtopr = savestack(L, oldtop);
      setsvalue2s(L, restorestack(L, oldtopr), luaS_newliteral(L, "error in error handling"));
      break;
    }
    case LUA_ERRSYNTAX:
    case LUA_ERRRUN: {
      setobjs2s(L, oldtop, L->top - 1);  /* error message on current top */
      break;
    }
  }
  L->top = oldtop + 1;
}

static int call_binTM (lua_State *L, const TObject *p1, const TObject *p2,
                       StkId res, TMS event) {
  ptrdiff_t result = savestack(L, res);
  const TObject *tm = luaT_gettmbyobj(L, p1, event);  /* try first operand */
  if (ttisnil(tm))
    tm = luaT_gettmbyobj(L, p2, event);  /* try second operand */
  if (!ttisfunction(tm)) return 0;
  callTMres(L, tm, p1, p2);
  res = restorestack(L, result);  /* previous call may change stack */
  setobjs2s(res, L->top);
  return 1;
}

int luaV_tostring (lua_State *L, StkId obj) {
  if (!ttisnumber(obj))
    return 0;
  else {
    char s[LUAI_MAXNUMBER2STR];
    ptrdiff_t objr = savestack(L, obj);
    lua_Number n = nvalue(obj);
    lua_number2str(s, n);
    setsvalue2s(L, restorestack(L, objr), luaS_new(L, s));
    return 1;
  }
}

static void callTMres (lua_State *L, StkId res, const TValue *f,
                        const TValue *p1, const TValue *p2) {
  ptrdiff_t result = savestack(L, res);
  setobj2s(L, L->top, f);  /* push function */
  setobj2s(L, L->top+1, p1);  /* 1st argument */
  setobj2s(L, L->top+2, p2);  /* 2nd argument */
  luaD_checkstack(L, 3);
  L->top += 3;
  luaD_call(L, L->top - 3, 1);
  res = restorestack(L, result);
  L->top--;
  setobjs2s(L, res, L->top);
}

/* Parse a number literal. */
static void lex_number(LexState *ls)
{
  StrScanFmt fmt;
  TValue *tv = &ls->tokenval;
  int c, xp = 'e';
  if (ls->current == '-' || ls->current == '+') {
    save_and_next(ls);
  }
  if ((c = ls->current) == '0') {
    save_and_next(ls);
    if ((ls->current | 0x20) == 'x') xp = 'p';
  }
  while (lj_char_isident(ls->current) || ls->current == '.' ||
	 ((ls->current == '-' || ls->current == '+') && (c | 0x20) == xp)) {
    c = ls->current;
    save_and_next(ls);
  }
  save(ls, '\0');
  fmt = lj_strscan_scan((const uint8_t *)ls->sb.buf, tv,
	  (LJ_DUALNUM ? STRSCAN_OPT_TOINT : STRSCAN_OPT_TONUM) |
	  (LJ_HASFFI ? (STRSCAN_OPT_LL|STRSCAN_OPT_IMAG) : 0));
  ls->token = TK_number;
  if (LJ_DUALNUM && fmt == STRSCAN_INT) {
    setitype(tv, LJ_TISNUM);
  } else if (fmt == STRSCAN_NUM) {
    /* Already in correct format. */
#if LJ_HASFFI
  } else if (fmt != STRSCAN_ERROR) {
    lua_State *L = ls->L;
    GCcdata *cd;
    lua_assert(fmt == STRSCAN_I64 || fmt == STRSCAN_U64 || fmt == STRSCAN_IMAG);
    if (!ctype_ctsG(G(L))) {
      ptrdiff_t oldtop = savestack(L, L->top);
      luaopen_ffi(L);  /* Load FFI library on-demand. */
      L->top = restorestack(L, oldtop);
    }
    if (fmt == STRSCAN_IMAG) {
      cd = lj_cdata_new_(L, CTID_COMPLEX_DOUBLE, 2*sizeof(double));
      ((double *)cdataptr(cd))[0] = 0;
      ((double *)cdataptr(cd))[1] = numV(tv);
    } else {
      cd = lj_cdata_new_(L, fmt==STRSCAN_I64 ? CTID_INT64 : CTID_UINT64, 8);
      *(uint64_t *)cdataptr(cd) = tv->u64;
    }
    lj_parse_keepcdata(ls, tv, cd);
#endif
  } else {
    lua_assert(fmt == STRSCAN_ERROR);
    lj_lex_error(ls, TK_number, LJ_ERR_XNUMBER);
  }
}

static int precall(ktap_state *ks, StkId func, int nresults)
{
	ktap_cfunction f;
	ktap_callinfo *ci;
	ktap_proto *p;
	StkId base;
	ptrdiff_t funcr = savestack(ks, func);
	int n;

	switch (ttype(func)) {
	case KTAP_TLCF: /* light C function */
		f = fvalue(func);
		goto CFUNC;
	case KTAP_TCCL: /* C closure */
		f = clcvalue(func)->f;
 CFUNC:
		checkstack(ks, KTAP_MINSTACK);
		ci = next_ci(ks);
		ci->nresults = nresults;
		ci->func = restorestack(ks, funcr);
		ci->top = ks->top + KTAP_MINSTACK;
		ci->callstatus = 0;
		n = (*f)(ks);
		poscall(ks, ks->top - n);
		return 1;
	case KTAP_TLCL:	
		p = CLVALUE(func)->p;
		checkstack(ks, p->maxstacksize);
		func = restorestack(ks, funcr);
		n = (int)(ks->top - func) - 1; /* number of real arguments */

		/* complete missing arguments */
		for (; n < p->numparams; n++)
			setnilvalue(ks->top++);

		base = (!p->is_vararg) ? func + 1 : adjust_varargs(ks, p, n);
		ci = next_ci(ks);
		ci->nresults = nresults;
		ci->func = func;
		ci->u.l.base = base;
		ci->top = base + p->maxstacksize;
		ci->u.l.savedpc = p->code; /* starting point */
		ci->callstatus = CIST_KTAP;
		ks->top = ci->top;
		return 0;
	default:
		kp_error(ks, "attempt to call nil function\n");
	}

	return 0;
}

/* Find error function for runtime errors. Requires an extra stack traversal. */
static ptrdiff_t finderrfunc(lua_State *L)
{
  cTValue *frame = L->base-1, *bot = tvref(L->stack);
  void *cf = L->cframe;
  while (frame > bot && cf) {
    while (cframe_nres(cframe_raw(cf)) < 0) {  /* cframe without frame? */
      if (frame >= restorestack(L, -cframe_nres(cf)))
	break;
      if (cframe_errfunc(cf) >= 0)  /* Error handler not inherited (-1)? */
	return cframe_errfunc(cf);
      cf = cframe_prev(cf);  /* Else unwind cframe and continue searching. */
      if (cf == NULL)
	return 0;
    }
    switch (frame_typep(frame)) {
    case FRAME_LUA:
    case FRAME_LUAP:
      frame = frame_prevl(frame);
      break;
    case FRAME_C:
      cf = cframe_prev(cf);
      /* fallthrough */
    case FRAME_VARG:
      frame = frame_prevd(frame);
      break;
    case FRAME_CONT:
#if LJ_HASFFI
      if ((frame-1)->u32.lo == LJ_CONT_FFI_CALLBACK)
	cf = cframe_prev(cf);
#endif
      frame = frame_prevd(frame);
      break;
    case FRAME_CP:
      if (cframe_canyield(cf)) return 0;
      if (cframe_errfunc(cf) >= 0)
	return cframe_errfunc(cf);
      frame = frame_prevd(frame);
      break;
    case FRAME_PCALL:
    case FRAME_PCALLH:
      if (frame_ftsz(frame) >= (ptrdiff_t)(2*sizeof(TValue)))  /* xpcall? */
	return savestack(L, frame-1);  /* Point to xpcall's errorfunc. */
      return 0;
    default:
      lua_assert(0);
      return 0;
    }
  }
  return 0;
}

void luaT_callTM (lua_State *L, const TValue *f, const TValue *p1,
                  const TValue *p2, TValue *p3, int hasres) {
  ptrdiff_t result = savestack(L, p3);
  setobj2s(L, L->top++, f);  /* push function (assume EXTRA_STACK) */
  setobj2s(L, L->top++, p1);  /* 1st argument */
  setobj2s(L, L->top++, p2);  /* 2nd argument */
  if (!hasres)  /* no result? 'p3' is third argument */
    setobj2s(L, L->top++, p3);  /* 3rd argument */
  /* metamethod may yield only when called from Lua code */
  luaD_call(L, L->top - (4 - hasres), hasres, isLua(L->ci));
  if (hasres) {  /* if has result, move it to its place */
    p3 = restorestack(L, result);
    setobjs2s(L, p3, --L->top);
  }
}

/* Find error function for runtime errors. Requires an extra stack traversal. */
static ptrdiff_t finderrfunc(lua_State *L)
{
  cTValue *frame = L->base-1, *bot = tvref(L->stack)+LJ_FR2;
  void *cf = L->cframe;
  while (frame > bot && cf) {
    while (cframe_nres(cframe_raw(cf)) < 0) {  /* cframe without frame? */
      if (frame >= restorestack(L, -cframe_nres(cf)))
	break;
      if (cframe_errfunc(cf) >= 0)  /* Error handler not inherited (-1)? */
	return cframe_errfunc(cf);
      cf = cframe_prev(cf);  /* Else unwind cframe and continue searching. */
      if (cf == NULL)
	return 0;
    }
    switch (frame_typep(frame)) {
    case FRAME_LUA:
    case FRAME_LUAP:
      frame = frame_prevl(frame);
      break;
    case FRAME_C:
      cf = cframe_prev(cf);
      /* fallthrough */
    case FRAME_VARG:
      frame = frame_prevd(frame);
      break;
    case FRAME_CONT:
      if (frame_iscont_fficb(frame))
	cf = cframe_prev(cf);
      frame = frame_prevd(frame);
      break;
    case FRAME_CP:
      if (cframe_canyield(cf)) return 0;
      if (cframe_errfunc(cf) >= 0)
	return cframe_errfunc(cf);
      frame = frame_prevd(frame);
      break;
    case FRAME_PCALL:
    case FRAME_PCALLH:
      if (frame_func(frame_prevd(frame))->c.ffid == FF_xpcall)
	return savestack(L, frame_prevd(frame)+1);  /* xpcall's errorfunc. */
      return 0;
    default:
      lua_assert(0);
      return 0;
    }
  }
  return 0;
}

void luaT_callTMres (lua_State *L, const TValue *f, const TValue *p1,
                     const TValue *p2, StkId res) {
  ptrdiff_t result = savestack(L, res);
  StkId func = L->top;
  setobj2s(L, func, f);  /* push function (assume EXTRA_STACK) */
  setobj2s(L, func + 1, p1);  /* 1st argument */
  setobj2s(L, func + 2, p2);  /* 2nd argument */
  L->top += 3;
  /* metamethod may yield only when called from Lua code */
  if (isLuacode(L->ci))
    luaD_call(L, func, 1);
  else
    luaD_callnoyield(L, func, 1);
  res = restorestack(L, result);
  setobjs2s(L, res, --L->top);  /* move result to its place */
}

ptrdiff_t lj_vmevent_prepare(lua_State *L, VMEvent ev)
{
  global_State *g = G(L);
  GCstr *s = lj_str_newlit(L, LJ_VMEVENTS_REGKEY);
  cTValue *tv = lj_tab_getstr(tabV(registry(L)), s);
  if (tvistab(tv)) {
    int hash = VMEVENT_HASH(ev);
    tv = lj_tab_getint(tabV(tv), hash);
    if (tv && tvisfunc(tv)) {
      lj_state_checkstack(L, LUA_MINSTACK);
      setfuncV(L, L->top++, funcV(tv));
      return savestack(L, L->top);
    }
  }
  g->vmevmask &= ~VMEVENT_MASK(ev);  /* No handler: cache this fact. */
  return 0;
}