text: /*
  ** $Id: ldo.c,v 2.157 2016/12/13 15:52:21 roberto Exp $
  ** Stack and Call structure of Lua
  ** See Copyright Notice in lua.hpp
  */
  
  #define ldo_c
  #define LUA_CORE
  
  #include "lprefix.hpp"
  
  
  #include <setjmp.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "lua.hpp"
  
  #include "lapi.hpp"
  #include "ldebug.hpp"
  #include "ldo.hpp"
  #include "lfunc.hpp"
  #include "lgc.hpp"
  #include "lmem.hpp"
  #include "lobject.hpp"
  #include "lopcodes.hpp"
  #include "lparser.hpp"
  #include "lstate.hpp"
  #include "lstring.hpp"
  #include "ltable.hpp"
  #include "ltm.hpp"
  #include "lundump.hpp"
  #include "lvm.hpp"
  #include "lzio.hpp"
  
  
  
  #define errorstatus(s)	((s) > LUA_YIELD)
  
  
  /*
  ** {======================================================
  ** Error-recovery functions
  ** =======================================================
  */
  
  /*
  ** LUAI_THROW/LUAI_TRY define how Lua does exception handling. By
  ** default, Lua handles errors with exceptions when compiling as
  ** C++ code, with _longjmp/_setjmp when asked to use them, and with
  ** longjmp/setjmp otherwise.
  */
  #if !defined(LUAI_THROW)				/* { */
  
  #if defined(__cplusplus) && !defined(LUA_USE_LONGJMP)	/* { */
  
  /* C++ exceptions */
  #define LUAI_THROW(L,c)		throw(c)
  #define LUAI_TRY(L,c,a) \
  	try { a } catch(...) { if ((c)->status == 0) (c)->status = -1; }
  #define luai_jmpbuf		int  /* dummy variable */
  
  #elif defined(LUA_USE_POSIX)				/* }{ */
  
  /* in POSIX, try _longjmp/_setjmp (more efficient) */
  #define LUAI_THROW(L,c)		_longjmp((c)->b, 1)
  #define LUAI_TRY(L,c,a)		if (_setjmp((c)->b) == 0) { a }
  #define luai_jmpbuf		jmp_buf
  
  #else							/* }{ */
  
  /* ISO C handling with long jumps */
  #define LUAI_THROW(L,c)		longjmp((c)->b, 1)
  #define LUAI_TRY(L,c,a)		if (setjmp((c)->b) == 0) { a }
  #define luai_jmpbuf		jmp_buf
  
  #endif							/* } */
  
  #endif							/* } */
  
  
  
  /* chain list of long jump buffers */
  struct lua_longjmp {
    struct lua_longjmp *previous;
    luai_jmpbuf b;
    volatile int status;  /* error code */
  };
  
  
  static void seterrorobj (lua_State *L, int errcode, StkId oldtop) {
    switch (errcode) {
      case LUA_ERRMEM: {  /* memory error? */
        setsvalue2s(L, oldtop, G(L)->memerrmsg); /* reuse preregistered msg. */
        break;
      }
      case LUA_ERRERR: {
        setsvalue2s(L, oldtop, luaS_newliteral(L, "error in error handling"));
        break;
      }
      default: {
        setobjs2s(L, oldtop, L->top - 1);  /* error message on current top */
        break;
      }
    }
    L->top = oldtop + 1;
  }
  
  
  l_noret luaD_throw (lua_State *L, int errcode) {
    if (L->errorJmp) {  /* thread has an error handler? */
      L->errorJmp->status = errcode;  /* set status */
      LUAI_THROW(L, L->errorJmp);  /* jump to it */
    }
    else {  /* thread has no error handler */
      global_State *g = G(L);
      L->status = cast_byte(errcode);  /* mark it as dead */
      if (g->mainthread->errorJmp) {  /* main thread has a handler? */
        setobjs2s(L, g->mainthread->top++, L->top - 1);  /* copy error obj. */
        luaD_throw(g->mainthread, errcode);  /* re-throw in main thread */
      }
      else {  /* no handler at all; abort */
        if (g->panic) {  /* panic function? */
          seterrorobj(L, errcode, L->top);  /* assume EXTRA_STACK */
          if (L->ci->top < L->top)
            L->ci->top = L->top;  /* pushing msg. can break this invariant */
          lua_unlock(L);
          g->panic(L);  /* call panic function (last chance to jump out) */
        }
        abort();
      }
    }
  }
  
  
  int luaD_rawrunprotected (lua_State *L, Pfunc f, void *ud) {
    unsigned short oldnCcalls = L->nCcalls;
    struct lua_longjmp lj;
    lj.status = LUA_OK;
    lj.previous = L->errorJmp;  /* chain new error handler */
    L->errorJmp = &lj;
    LUAI_TRY(L, &lj,
      (*f)(L, ud);
    );
    L->errorJmp = lj.previous;  /* restore old error handler */
    L->nCcalls = oldnCcalls;
    return lj.status;
  }
  
  /* }====================================================== */
  
  
  /*
  ** {==================================================================
  ** Stack reallocation
  ** ===================================================================
  */
  static void correctstack (lua_State *L, TValue *oldstack) {
    CallInfo *ci;
    UpVal *up;
    L->top = (L->top - oldstack) + L->stack;
    for (up = L->openupval; up != NULL; up = up->u.open.next)
      up->v = (up->v - oldstack) + L->stack;
    for (ci = L->ci; ci != NULL; ci = ci->previous) {
      ci->top = (ci->top - oldstack) + L->stack;
      ci->func = (ci->func - oldstack) + L->stack;
      if (isLua(ci))
        ci->u.l.base = (ci->u.l.base - oldstack) + L->stack;
    }
  }
  
  
  /* some space for error handling */
  #define ERRORSTACKSIZE	(LUAI_MAXSTACK + 200)
  
  
  void luaD_reallocstack (lua_State *L, int newsize) {
    TValue *oldstack = L->stack;
    int lim = L->stacksize;
    lua_assert(newsize <= LUAI_MAXSTACK || newsize == ERRORSTACKSIZE);
    lua_assert(L->stack_last - L->stack == L->stacksize - EXTRA_STACK);
    luaM_reallocvector(L, L->stack, L->stacksize, newsize, TValue);
    for (; lim < newsize; lim++)
      setnilvalue(L->stack + lim); /* erase new segment */
    L->stacksize = newsize;
    L->stack_last = L->stack + newsize - EXTRA_STACK;
    correctstack(L, oldstack);
  }
  
  
  void luaD_growstack (lua_State *L, int n) {
    int size = L->stacksize;
    if (size > LUAI_MAXSTACK)  /* error after extra size? */
      luaD_throw(L, LUA_ERRERR);
    else {
      int needed = cast_int(L->top - L->stack) + n + EXTRA_STACK;
      int newsize = 2 * size;
      if (newsize > LUAI_MAXSTACK) newsize = LUAI_MAXSTACK;
      if (newsize < needed) newsize = needed;
      if (newsize > LUAI_MAXSTACK) {  /* stack overflow? */
        luaD_reallocstack(L, ERRORSTACKSIZE);
        luaG_runerror(L, "stack overflow");
      }
      else
        luaD_reallocstack(L, newsize);
    }
  }
  
  
  static int stackinuse (lua_State *L) {
    CallInfo *ci;
    StkId lim = L->top;
    for (ci = L->ci; ci != NULL; ci = ci->previous) {
      if (lim < ci->top) lim = ci->top;
    }
    lua_assert(lim <= L->stack_last);
    return cast_int(lim - L->stack) + 1;  /* part of stack in use */
  }
  
  
  void luaD_shrinkstack (lua_State *L) {
    int inuse = stackinuse(L);
    int goodsize = inuse + (inuse / 8) + 2*EXTRA_STACK;
    if (goodsize > LUAI_MAXSTACK)
      goodsize = LUAI_MAXSTACK;  /* respect stack limit */
    if (L->stacksize > LUAI_MAXSTACK)  /* had been handling stack overflow? */
      luaE_freeCI(L);  /* free all CIs (list grew because of an error) */
    else
      luaE_shrinkCI(L);  /* shrink list */
    /* if thread is currently not handling a stack overflow and its
       good size is smaller than current size, shrink its stack */
    if (inuse <= (LUAI_MAXSTACK - EXTRA_STACK) &&
        goodsize < L->stacksize)
      luaD_reallocstack(L, goodsize);
    else  /* don't change stack */
      condmovestack(L,{},{});  /* (change only for debugging) */
  }
  
  
  void luaD_inctop (lua_State *L) {
    luaD_checkstack(L, 1);
    L->top++;
  }
  
  /* }================================================================== */
  
  
  /*
  ** Call a hook for the given event. Make sure there is a hook to be
  ** called. (Both 'L->hook' and 'L->hookmask', which triggers this
  ** function, can be changed asynchronously by signals.)
  */
  void luaD_hook (lua_State *L, int event, int line) {
    lua_Hook hook = L->hook;
    if (hook && L->allowhook) {  /* make sure there is a hook */
      CallInfo *ci = L->ci;
      ptrdiff_t top = savestack(L, L->top);
      ptrdiff_t ci_top = savestack(L, ci->top);
      lua_Debug ar;
      ar.event = event;
      ar.currentline = line;
      ar.i_ci = ci;
      luaD_checkstack(L, LUA_MINSTACK);  /* ensure minimum stack size */
      ci->top = L->top + LUA_MINSTACK;
      lua_assert(ci->top <= L->stack_last);
      L->allowhook = 0;  /* cannot call hooks inside a hook */
      ci->callstatus |= CIST_HOOKED;
      lua_unlock(L);
      (*hook)(L, &ar);
      lua_lock(L);
      lua_assert(!L->allowhook);
      L->allowhook = 1;
      ci->top = restorestack(L, ci_top);
      L->top = restorestack(L, top);
      ci->callstatus &= ~CIST_HOOKED;
    }
  }
  
  
  static void callhook (lua_State *L, CallInfo *ci) {
    int hook = LUA_HOOKCALL;
    ci->u.l.savedpc++;  /* hooks assume 'pc' is already incremented */
    if (isLua(ci->previous) &&
        GET_OPCODE(*(ci->previous->u.l.savedpc - 1)) == OP_TAILCALL) {
      ci->callstatus |= CIST_TAIL;
      hook = LUA_HOOKTAILCALL;
    }
    luaD_hook(L, hook, -1);
    ci->u.l.savedpc--;  /* correct 'pc' */
  }
  
  
  static StkId adjust_varargs (lua_State *L, Proto *p, int actual) {
    int i;
    int nfixargs = p->numparams;
    StkId base, fixed;
    /* move fixed parameters to final position */
    fixed = L->top - actual;  /* first fixed argument */
    base = L->top;  /* final position of first argument */
    for (i = 0; i < nfixargs && i < actual; i++) {
      setobjs2s(L, L->top++, fixed + i);
      setnilvalue(fixed + i);  /* erase original copy (for GC) */
    }
    for (; i < nfixargs; i++)
      setnilvalue(L->top++);  /* complete missing arguments */
    return base;
  }
  
  
  /*
  ** Check whether __call metafield of 'func' is a function. If so, put
  ** it in stack below original 'func' so that 'luaD_precall' can call
  ** it. Raise an error if __call metafield is not a function.
  */
  static void tryfuncTM (lua_State *L, StkId func) {
    const TValue *tm = luaT_gettmbyobj(L, func, TM_CALL);
    StkId p;
    if (!ttisfunction(tm))
      luaG_typeerror(L, func, "call");
    /* Open a hole inside the stack at 'func' */
    for (p = L->top; p > func; p--)
      setobjs2s(L, p, p-1);
    L->top++;  /* slot ensured by caller */
    setobj2s(L, func, tm);  /* tag method is the new function to be called */
  }
  
  
  /*
  ** Given 'nres' results at 'firstResult', move 'wanted' of them to 'res'.
  ** Handle most typical cases (zero results for commands, one result for
  ** expressions, multiple results for tail calls/single parameters)
  ** separated.
  */
  static int moveresults (lua_State *L, const TValue *firstResult, StkId res,
                                        int nres, int wanted) {
    switch (wanted) {  /* handle typical cases separately */
      case 0: break;  /* nothing to move */
      case 1: {  /* one result needed */
        if (nres == 0)   /* no results? */
          firstResult = luaO_nilobject;  /* adjust with nil */
        setobjs2s(L, res, firstResult);  /* move it to proper place */
        break;
      }
      case LUA_MULTRET: {
        int i;
        for (i = 0; i < nres; i++)  /* move all results to correct place */
          setobjs2s(L, res + i, firstResult + i);
        L->top = res + nres;
        return 0;  /* wanted == LUA_MULTRET */
      }
      default: {
        int i;
        if (wanted <= nres) {  /* enough results? */
          for (i = 0; i < wanted; i++)  /* move wanted results to correct place */
            setobjs2s(L, res + i, firstResult + i);
        }
        else {  /* not enough results; use all of them plus nils */
          for (i = 0; i < nres; i++)  /* move all results to correct place */
            setobjs2s(L, res + i, firstResult + i);
          for (; i < wanted; i++)  /* complete wanted number of results */
            setnilvalue(res + i);
        }
        break;
      }
    }
    L->top = res + wanted;  /* top points after the last result */
    return 1;
  }
  
  
  /*
  ** Finishes a function call: calls hook if necessary, removes CallInfo,
  ** moves current number of results to proper place; returns 0 iff call
  ** wanted multiple (variable number of) results.
  */
  int luaD_poscall (lua_State *L, CallInfo *ci, StkId firstResult, int nres) {
    StkId res;
    int wanted = ci->nresults;
    if (L->hookmask & (LUA_MASKRET | LUA_MASKLINE)) {
      if (L->hookmask & LUA_MASKRET) {
        ptrdiff_t fr = savestack(L, firstResult);  /* hook may change stack */
        luaD_hook(L, LUA_HOOKRET, -1);
        firstResult = restorestack(L, fr);
      }
      L->oldpc = ci->previous->u.l.savedpc;  /* 'oldpc' for caller function */
    }
    res = ci->func;  /* res == final position of 1st result */
    L->ci = ci->previous;  /* back to caller */
    /* move results to proper place */
    return moveresults(L, firstResult, res, nres, wanted);
  }
  
  
  
  #define next_ci(L) (L->ci = (L->ci->next ? L->ci->next : luaE_extendCI(L)))
  
  
  /* macro to check stack size, preserving 'p' */
  #define checkstackp(L,n,p)  \
    luaD_checkstackaux(L, n, \
      ptrdiff_t t__ = savestack(L, p);  /* save 'p' */ \
      luaC_checkGC(L),  /* stack grow uses memory */ \
      p = restorestack(L, t__))  /* 'pos' part: restore 'p' */
  
  
  /*
  ** Prepares a function call: checks the stack, creates a new CallInfo
  ** entry, fills in the relevant information, calls hook if needed.
  ** If function is a C function, does the call, too. (Otherwise, leave
  ** the execution ('luaV_execute') to the caller, to allow stackless
  ** calls.) Returns true iff function has been executed (C function).
  */
  int luaD_precall (lua_State *L, StkId func, int nresults) {
    lua_CFunction f;
    CallInfo *ci;
    switch (ttype(func)) {
      case LUA_TCCL:  /* C closure */
        f = clCvalue(func)->f;
        goto Cfunc;
      case LUA_TLCF:  /* light C function */
        f = fvalue(func);
       Cfunc: {
        int n;  /* number of returns */
        checkstackp(L, LUA_MINSTACK, func);  /* ensure minimum stack size */
        ci = next_ci(L);  /* now 'enter' new function */
        ci->nresults = nresults;
        ci->func = func;
        ci->top = L->top + LUA_MINSTACK;
        lua_assert(ci->top <= L->stack_last);
        ci->callstatus = 0;
        if (L->hookmask & LUA_MASKCALL)
          luaD_hook(L, LUA_HOOKCALL, -1);
        lua_unlock(L);
        n = (*f)(L);  /* do the actual call */
        lua_lock(L);
        api_checknelems(L, n);
        luaD_poscall(L, ci, L->top - n, n);
        return 1;
      }
      case LUA_TLCL: {  /* Lua function: prepare its call    准备呼叫LUA 函数*/
        StkId base;
        Proto *p = clLvalue(func)->p;
        int n = cast_int(L->top - func) - 1;  /* number of real arguments   实参个数*/
        int fsize = p->maxstacksize;  /* frame size */
        checkstackp(L, fsize, func);
        if (p->is_vararg)              //   是否是可变参数
          base = adjust_varargs(L, p, n);
        else {  /* non vararg function */
          for (; n < p->numparams; n++)
            setnilvalue(L->top++);  /* complete missing arguments   完善 缺失的 参数 */
          base = func + 1;
        }
        ci = next_ci(L);  /* now 'enter' new function 进入新的函数*/
        ci->nresults = nresults;  /* 可能的返回值个数 */
        ci->func = func;
        ci->u.l.base = base;
        L->top = ci->top = base + fsize;
        lua_assert(ci->top <= L->stack_last);
        ci->u.l.savedpc = p->code;  /* starting point */
        ci->callstatus = CIST_LUA;
        if (L->hookmask & LUA_MASKCALL)
          callhook(L, ci);
        return 0;
      }
      default: {  /* not a function */
        checkstackp(L, 1, func);  /* ensure space for metamethod */
        tryfuncTM(L, func);  /* try to get '__call' metamethod */
        return luaD_precall(L, func, nresults);  /* now it must be a function */
      }
    }
  }
  
  
  /*
  ** Check appropriate error for stack overflow ("regular" overflow or
  ** overflow while handling stack overflow). If 'nCalls' is larger than
  ** LUAI_MAXCCALLS (which means it is handling a "regular" overflow) but
  ** smaller than 9/8 of LUAI_MAXCCALLS, does not report an error (to
  ** allow overflow handling to work)
  */
  static void stackerror (lua_State *L) {
    if (L->nCcalls == LUAI_MAXCCALLS)
      luaG_runerror(L, "C stack overflow");
    else if (L->nCcalls >= (LUAI_MAXCCALLS + (LUAI_MAXCCALLS>>3)))
      luaD_throw(L, LUA_ERRERR);  /* error while handing stack error */
  }
  
  
  /*
  ** Call a function (C or Lua). The function to be called is at *func.
  ** The arguments are on the stack, right after the function.
  ** When returns, all the results are on the stack, starting at the original
  ** function position.
  */
  void luaD_call (lua_State *L, StkId func, int nResults) {
    if (++L->nCcalls >= LUAI_MAXCCALLS)
      stackerror(L);
    if (!luaD_precall(L, func, nResults))  /* is a Lua function? */
      luaV_execute(L);  /* call it *///  执行函数  
    L->nCcalls--;
  }
  
  
  /*
  ** Similar to 'luaD_call', but does not allow yields during the call
  */
  void luaD_callnoyield (lua_State *L, StkId func, int nResults) {
    L->nny++;
    luaD_call(L, func, nResults);
    L->nny--;
  }
  
  
  /*
  ** Completes the execution of an interrupted C function, calling its
  ** continuation function.
  */
  static void finishCcall (lua_State *L, int status) {
    CallInfo *ci = L->ci;
    int n;
    /* must have a continuation and must be able to call it */
    lua_assert(ci->u.c.k != NULL && L->nny == 0);
    /* error status can only happen in a protected call */
    lua_assert((ci->callstatus & CIST_YPCALL) || status == LUA_YIELD);
    if (ci->callstatus & CIST_YPCALL) {  /* was inside a pcall? */
      ci->callstatus &= ~CIST_YPCALL;  /* continuation is also inside it */
      L->errfunc = ci->u.c.old_errfunc;  /* with the same error function */
    }
    /* finish 'lua_callk'/'lua_pcall'; CIST_YPCALL and 'errfunc' already
       handled */
    adjustresults(L, ci->nresults);
    lua_unlock(L);
    n = (*ci->u.c.k)(L, status, ci->u.c.ctx);  /* call continuation function */
    lua_lock(L);
    api_checknelems(L, n);
    luaD_poscall(L, ci, L->top - n, n);  /* finish 'luaD_precall' */
  }
  
  
  /*
  ** Executes "full continuation" (everything in the stack) of a
  ** previously interrupted coroutine until the stack is empty (or another
  ** interruption long-jumps out of the loop). If the coroutine is
  ** recovering from an error, 'ud' points to the error status, which must
  ** be passed to the first continuation function (otherwise the default
  ** status is LUA_YIELD).
  */
  static void unroll (lua_State *L, void *ud) {
    if (ud != NULL)  /* error status? */
      finishCcall(L, *(int *)ud);  /* finish 'lua_pcallk' callee */
    while (L->ci != &L->base_ci) {  /* something in the stack */
      if (!isLua(L->ci))  /* C function? */
        finishCcall(L, LUA_YIELD);  /* complete its execution */
      else {  /* Lua function */
        luaV_finishOp(L);  /* finish interrupted instruction */
        luaV_execute(L);  /* execute down to higher C 'boundary' */
      }
    }
  }
  
  
  /*
  ** Try to find a suspended protected call (a "recover point") for the
  ** given thread.
  */
  static CallInfo *findpcall (lua_State *L) {
    CallInfo *ci;
    for (ci = L->ci; ci != NULL; ci = ci->previous) {  /* search for a pcall */
      if (ci->callstatus & CIST_YPCALL)
        return ci;
    }
    return NULL;  /* no pending pcall */
  }
  
  
  /*
  ** Recovers from an error in a coroutine. Finds a recover point (if
  ** there is one) and completes the execution of the interrupted
  ** 'luaD_pcall'. If there is no recover point, returns zero.
  */
  static int recover (lua_State *L, int status) {
    StkId oldtop;
    CallInfo *ci = findpcall(L);
    if (ci == NULL) return 0;  /* no recovery point */
    /* "finish" luaD_pcall */
    oldtop = restorestack(L, ci->extra);
    luaF_close(L, oldtop);
    seterrorobj(L, status, oldtop);
    L->ci = ci;
    L->allowhook = getoah(ci->callstatus);  /* restore original 'allowhook' */
    L->nny = 0;  /* should be zero to be yieldable */
    luaD_shrinkstack(L);
    L->errfunc = ci->u.c.old_errfunc;
    return 1;  /* continue running the coroutine */
  }
  
  
  /*
  ** Signal an error in the call to 'lua_resume', not in the execution
  ** of the coroutine itself. (Such errors should not be handled by any
  ** coroutine error handler and should not kill the coroutine.)
  */
  static int resume_error (lua_State *L, const char *msg, int narg) {
    L->top -= narg;  /* remove args from the stack */
    setsvalue2s(L, L->top, luaS_new(L, msg));  /* push error message */
    api_incr_top(L);
    lua_unlock(L);
    return LUA_ERRRUN;
  }
  
  
  /*
  ** Do the work for 'lua_resume' in protected mode. Most of the work
  ** depends on the status of the coroutine: initial state, suspended
  ** inside a hook, or regularly suspended (optionally with a continuation
  ** function), plus erroneous cases: non-suspended coroutine or dead
  ** coroutine.
  */
  static void resume (lua_State *L, void *ud) {
    int n = *(cast(int*, ud));  /* number of arguments */
    StkId firstArg = L->top - n;  /* first argument */
    CallInfo *ci = L->ci;
    if (L->status == LUA_OK) {  /* starting a coroutine? */
      if (!luaD_precall(L, firstArg - 1, LUA_MULTRET))  /* Lua function? */
        luaV_execute(L);  /* call it */
    }
    else {  /* resuming from previous yield */
      lua_assert(L->status == LUA_YIELD);
      L->status = LUA_OK;  /* mark that it is running (again) */
      ci->func = restorestack(L, ci->extra);
      if (isLua(ci))  /* yielded inside a hook? */
        luaV_execute(L);  /* just continue running Lua code */
      else {  /* 'common' yield */
        if (ci->u.c.k != NULL) {  /* does it have a continuation function? */
          lua_unlock(L);
          n = (*ci->u.c.k)(L, LUA_YIELD, ci->u.c.ctx); /* call continuation */
          lua_lock(L);
          api_checknelems(L, n);
          firstArg = L->top - n;  /* yield results come from continuation */
        }
        luaD_poscall(L, ci, firstArg, n);  /* finish 'luaD_precall' */
      }
      unroll(L, NULL);  /* run continuation */
    }
  }
  
  
  LUA_API int lua_resume (lua_State *L, lua_State *from, int nargs) {
    int status;
    unsigned short oldnny = L->nny;  /* save "number of non-yieldable" calls */
    lua_lock(L);
    if (L->status == LUA_OK) {  /* may be starting a coroutine */
      if (L->ci != &L->base_ci)  /* not in base level? */
        return resume_error(L, "cannot resume non-suspended coroutine", nargs);
    }
    else if (L->status != LUA_YIELD)
      return resume_error(L, "cannot resume dead coroutine", nargs);
    L->nCcalls = (from) ? from->nCcalls + 1 : 1;
    if (L->nCcalls >= LUAI_MAXCCALLS)
      return resume_error(L, "C stack overflow", nargs);
    luai_userstateresume(L, nargs);
    L->nny = 0;  /* allow yields */
    api_checknelems(L, (L->status == LUA_OK) ? nargs + 1 : nargs);
    status = luaD_rawrunprotected(L, resume, &nargs);
    if (status == -1)  /* error calling 'lua_resume'? */
      status = LUA_ERRRUN;
    else {  /* continue running after recoverable errors */
      while (errorstatus(status) && recover(L, status)) {
        /* unroll continuation */
        status = luaD_rawrunprotected(L, unroll, &status);
      }
      if (errorstatus(status)) {  /* unrecoverable error? */
        L->status = cast_byte(status);  /* mark thread as 'dead' */
        seterrorobj(L, status, L->top);  /* push error message */
        L->ci->top = L->top;
      }
      else lua_assert(status == L->status);  /* normal end or yield */
    }
    L->nny = oldnny;  /* restore 'nny' */
    L->nCcalls--;
    lua_assert(L->nCcalls == ((from) ? from->nCcalls : 0));
    lua_unlock(L);
    return status;
  }
  
  
  LUA_API int lua_isyieldable (lua_State *L) {
    return (L->nny == 0);
  }
  
  
  LUA_API int lua_yieldk (lua_State *L, int nresults, lua_KContext ctx,
                          lua_KFunction k) {
    CallInfo *ci = L->ci;
    luai_userstateyield(L, nresults);
    lua_lock(L);
    api_checknelems(L, nresults);
    if (L->nny > 0) {
      if (L != G(L)->mainthread)
        luaG_runerror(L, "attempt to yield across a C-call boundary");
      else
        luaG_runerror(L, "attempt to yield from outside a coroutine");
    }
    L->status = LUA_YIELD;
    ci->extra = savestack(L, ci->func);  /* save current 'func' */
    if (isLua(ci)) {  /* inside a hook? */
      api_check(L, k == NULL, "hooks cannot continue after yielding");
    }
    else {
      if ((ci->u.c.k = k) != NULL)  /* is there a continuation? */
        ci->u.c.ctx = ctx;  /* save context */
      ci->func = L->top - nresults - 1;  /* protect stack below results */
      luaD_throw(L, LUA_YIELD);
    }
    lua_assert(ci->callstatus & CIST_HOOKED);  /* must be inside a hook */
    lua_unlock(L);
    return 0;  /* return to 'luaD_hook' */
  }
  
  
  int luaD_pcall (lua_State *L, Pfunc func, void *u,
                  ptrdiff_t old_top, ptrdiff_t ef) {
    int status;
    CallInfo *old_ci = L->ci;
    lu_byte old_allowhooks = L->allowhook;
    unsigned short old_nny = L->nny;
    ptrdiff_t old_errfunc = L->errfunc;
    L->errfunc = ef;
    status = luaD_rawrunprotected(L, func, u);
    if (status != LUA_OK) {  /* an error occurred? */
      StkId oldtop = restorestack(L, old_top);
      luaF_close(L, oldtop);  /* close possible pending closures */
      seterrorobj(L, status, oldtop);
      L->ci = old_ci;
      L->allowhook = old_allowhooks;
      L->nny = old_nny;
      luaD_shrinkstack(L);
    }
    L->errfunc = old_errfunc;
    return status;
  }
  
  
  
  /*
  ** Execute a protected parser.
  */
  struct SParser {  /* data to 'f_parser' */
    ZIO *z;
    Mbuffer buff;  /* dynamic structure used by the scanner */
    Dyndata dyd;  /* dynamic structures used by the parser */
    const char *mode;
    const char *name;
  };
  
  
  static void checkmode (lua_State *L, const char *mode, const char *x) {
    if (mode && strchr(mode, x[0]) == NULL) {
      luaO_pushfstring(L,
         "attempt to load a %s chunk (mode is '%s')", x, mode);
      luaD_throw(L, LUA_ERRSYNTAX);
    }
  }
  
  
  static void f_parser (lua_State *L, void *ud) {
    LClosure *cl;
    struct SParser *p = cast(struct SParser *, ud);
    int c = zgetc(p->z);  /* read first character */
    if (c == LUA_SIGNATURE[0]) {
      checkmode(L, p->mode, "binary");
      cl = luaU_undump(L, p->z, p->name);
    }
    else {
      checkmode(L, p->mode, "text");
      cl = luaY_parser(L, p->z, &p->buff, &p->dyd, p->name, c);
    }
    lua_assert(cl->nupvalues == cl->p->sizeupvalues);
    luaF_initupvals(L, cl);
  }
  
  
  int luaD_protectedparser (lua_State *L, ZIO *z, const char *name,
                                          const char *mode) {
    struct SParser p;
    int status;
    L->nny++;  /* cannot yield during parsing */
    p.z = z; p.name = name; p.mode = mode;
    p.dyd.actvar.arr = NULL; p.dyd.actvar.size = 0;
    p.dyd.gt.arr = NULL; p.dyd.gt.size = 0;
    p.dyd.label.arr = NULL; p.dyd.label.size = 0;
    luaZ_initbuffer(L, &p.buff);
    status = luaD_pcall(L, f_parser, &p, savestack(L, L->top), L->errfunc);
    luaZ_freebuffer(L, &p.buff);
    luaM_freearray(L, p.dyd.actvar.arr, p.dyd.actvar.size);
    luaM_freearray(L, p.dyd.gt.arr, p.dyd.gt.size);
    luaM_freearray(L, p.dyd.label.arr, p.dyd.label.size);
    L->nny--;
    return status;
  }
  
  
  