text: /*
  ** $Id: ldo.c $
  ** Stack and Call structure of Lua
  ** See Copyright Notice in lua.h
  */
  
  #define ldo_c
  #define LUA_CORE
  
  #include "lprefix.h"
  
  
  #include <setjmp.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "lua.h"
  
  #include "lapi.h"
  #include "ldebug.h"
  #include "ldo.h"
  #include "lfunc.h"
  #include "lgc.h"
  #include "lmem.h"
  #include "lobject.h"
  #include "lopcodes.h"
  #include "lparser.h"
  #include "lstate.h"
  #include "lstring.h"
  #include "ltable.h"
  #include "ltm.h"
  #include "lundump.h"
  #include "lvm.h"
  #include "lzio.h"
  
  
  
  #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 */
  };
  
  
  void luaD_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;
      }
      case CLOSEPROTECT: {
        setnilvalue(s2v(oldtop));  /* no error message */
        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);
      errcode = luaF_close(L, L->stack, errcode);  /* close all upvalues */
      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? */
          luaD_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) {
    global_State *g = G(L);
    l_uint32 oldnCcalls = g->Cstacklimit - (L->nCcalls + L->nci);
    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 = g->Cstacklimit - oldnCcalls - L->nci;
    return lj.status;
  }
  
  /* }====================================================== */
  
  
  /*
  ** {==================================================================
  ** Stack reallocation
  ** ===================================================================
  */
  static void correctstack (lua_State *L, StkId oldstack, StkId newstack) {
    CallInfo *ci;
    UpVal *up;
    if (oldstack == newstack)
      return;  /* stack address did not change */
    L->top = (L->top - oldstack) + newstack;
    for (up = L->openupval; up != NULL; up = up->u.open.next)
      up->v = s2v((uplevel(up) - oldstack) + newstack);
    for (ci = L->ci; ci != NULL; ci = ci->previous) {
      ci->top = (ci->top - oldstack) + newstack;
      ci->func = (ci->func - oldstack) + newstack;
      if (isLua(ci))
        ci->u.l.trap = 1;  /* signal to update 'trap' in 'luaV_execute' */
    }
  }
  
  
  /* some space for error handling */
  #define ERRORSTACKSIZE	(LUAI_MAXSTACK + 200)
  
  
  int luaD_reallocstack (lua_State *L, int newsize, int raiseerror) {
    int lim = L->stacksize;
    StkId newstack = luaM_reallocvector(L, L->stack, lim, newsize, StackValue);
    lua_assert(newsize <= LUAI_MAXSTACK || newsize == ERRORSTACKSIZE);
    lua_assert(L->stack_last - L->stack == L->stacksize - EXTRA_STACK);
    if (unlikely(newstack == NULL)) {  /* reallocation failed? */
      if (raiseerror)
        luaM_error(L);
      else return 0;  /* do not raise an error */
    }
    for (; lim < newsize; lim++)
      setnilvalue(s2v(newstack + lim)); /* erase new segment */
    correctstack(L, L->stack, newstack);
    L->stack = newstack;
    L->stacksize = newsize;
    L->stack_last = L->stack + newsize - EXTRA_STACK;
    return 1;
  }
  
  
  /*
  ** Try to grow the stack by at least 'n' elements. when 'raiseerror'
  ** is true, raises any error; otherwise, return 0 in case of errors.
  */
  int luaD_growstack (lua_State *L, int n, int raiseerror) {
    int size = L->stacksize;
    int newsize = 2 * size;  /* tentative new size */
    if (unlikely(size > LUAI_MAXSTACK)) {  /* need more space after extra size? */
      if (raiseerror)
        luaD_throw(L, LUA_ERRERR);  /* error inside message handler */
      else return 0;
    }
    else {
      int needed = cast_int(L->top - L->stack) + n + EXTRA_STACK;
      if (newsize > LUAI_MAXSTACK)  /* cannot cross the limit */
        newsize = LUAI_MAXSTACK;
      if (newsize < needed)  /* but must respect what was asked for */
        newsize = needed;
      if (unlikely(newsize > LUAI_MAXSTACK)) {  /* stack overflow? */
        /* add extra size to be able to handle the error message */
        luaD_reallocstack(L, ERRORSTACKSIZE, raiseerror);
        if (raiseerror)
          luaG_runerror(L, "stack overflow");
        else return 0;
      }
    }  /* else no errors */
    return luaD_reallocstack(L, newsize, raiseerror);
  }
  
  
  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 + BASIC_STACK_SIZE;
    if (goodsize > LUAI_MAXSTACK)
      goodsize = LUAI_MAXSTACK;  /* respect stack limit */
    /* 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, 0);  /* ok if that fails */
    else  /* don't change stack */
      condmovestack(L,{},{});  /* (change only for debugging) */
    luaE_shrinkCI(L);  /* shrink CI list */
  }
  
  
  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 trigger this
  ** function, can be changed asynchronously by signals.)
  */
  void luaD_hook (lua_State *L, int event, int line,
                                int ftransfer, int ntransfer) {
    lua_Hook hook = L->hook;
    if (hook && L->allowhook) {  /* make sure there is a hook */
      int mask = CIST_HOOKED;
      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;
      if (ntransfer != 0) {
        mask |= CIST_TRAN;  /* 'ci' has transfer information */
        ci->u2.transferinfo.ftransfer = ftransfer;
        ci->u2.transferinfo.ntransfer = ntransfer;
      }
      luaD_checkstack(L, LUA_MINSTACK);  /* ensure minimum stack size */
      if (L->top + LUA_MINSTACK > ci->top)
        ci->top = L->top + LUA_MINSTACK;
      L->allowhook = 0;  /* cannot call hooks inside a hook */
      ci->callstatus |= mask;
      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 &= ~mask;
    }
  }
  
  
  /*
  ** Executes a call hook for Lua functions. This function is called
  ** whenever 'hookmask' is not zero, so it checks whether call hooks are
  ** active.
  */
  void luaD_hookcall (lua_State *L, CallInfo *ci) {
    int hook = (ci->callstatus & CIST_TAIL) ? LUA_HOOKTAILCALL : LUA_HOOKCALL;
    Proto *p;
    if (!(L->hookmask & LUA_MASKCALL))  /* some other hook? */
      return;  /* don't call hook */
    p = clLvalue(s2v(ci->func))->p;
    L->top = ci->top;  /* prepare top */
    ci->u.l.savedpc++;  /* hooks assume 'pc' is already incremented */
    luaD_hook(L, hook, -1, 1, p->numparams);
    ci->u.l.savedpc--;  /* correct 'pc' */
  }
  
  
  static StkId rethook (lua_State *L, CallInfo *ci, StkId firstres, int nres) {
    ptrdiff_t oldtop = savestack(L, L->top);  /* hook may change top */
    int delta = 0;
    if (isLuacode(ci)) {
      Proto *p = ci_func(ci)->p;
      if (p->is_vararg)
        delta = ci->u.l.nextraargs + p->numparams + 1;
      if (L->top < ci->top)
        L->top = ci->top;  /* correct top to run hook */
    }
    if (L->hookmask & LUA_MASKRET) {  /* is return hook on? */
      int ftransfer;
      ci->func += delta;  /* if vararg, back to virtual 'func' */
      ftransfer = cast(unsigned short, firstres - ci->func);
      luaD_hook(L, LUA_HOOKRET, -1, ftransfer, nres);  /* call it */
      ci->func -= delta;
    }
    if (isLua(ci = ci->previous))
      L->oldpc = pcRel(ci->u.l.savedpc, ci_func(ci)->p);  /* update 'oldpc' */
    return restorestack(L, oldtop);
  }
  
  
  /*
  ** Check whether 'func' has a '__call' metafield. If so, put it in the
  ** stack, below original 'func', so that 'luaD_call' can call it. Raise
  ** an error if there is no '__call' metafield.
  */
  void luaD_tryfuncTM (lua_State *L, StkId func) {
    const TValue *tm = luaT_gettmbyobj(L, s2v(func), TM_CALL);
    StkId p;
    if (unlikely(ttisnil(tm)))
      luaG_typeerror(L, s2v(func), "call");  /* nothing to call */
    for (p = L->top; p > func; p--)  /* open space for metamethod */
      setobjs2s(L, p, p-1);
    L->top++;  /* stack space pre-allocated by the caller */
    setobj2s(L, func, tm);  /* metamethod 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 void moveresults (lua_State *L, StkId res, int nres, int wanted) {
    StkId firstresult;
    int i;
    switch (wanted) {  /* handle typical cases separately */
      case 0:  /* no values needed */
        L->top = res;
        return;
      case 1:  /* one value needed */
        if (nres == 0)   /* no results? */
          setnilvalue(s2v(res));  /* adjust with nil */
        else
          setobjs2s(L, res, L->top - nres);  /* move it to proper place */
        L->top = res + 1;
        return;
      case LUA_MULTRET:
        wanted = nres;  /* we want all results */
        break;
      default:  /* multiple results (or to-be-closed variables) */
        if (hastocloseCfunc(wanted)) {  /* to-be-closed variables? */
          ptrdiff_t savedres = savestack(L, res);
          luaF_close(L, res, LUA_OK);  /* may change the stack */
          res = restorestack(L, savedres);
          wanted = codeNresults(wanted);  /* correct value */
          if (wanted == LUA_MULTRET)
            wanted = nres;
        }
        break;
    }
    firstresult = L->top - nres;  /* index of first result */
    /* move all results to correct place */
    for (i = 0; i < nres && i < wanted; i++)
      setobjs2s(L, res + i, firstresult + i);
    for (; i < wanted; i++)  /* complete wanted number of results */
      setnilvalue(s2v(res + i));
    L->top = res + wanted;  /* top points after the last result */
  }
  
  
  /*
  ** Finishes a function call: calls hook if necessary, removes CallInfo,
  ** moves current number of results to proper place.
  */
  void luaD_poscall (lua_State *L, CallInfo *ci, int nres) {
    if (L->hookmask)
      L->top = rethook(L, ci, L->top - nres, nres);
    L->ci = ci->previous;  /* back to caller */
    /* move results to proper place */
    moveresults(L, ci->func, nres, ci->nresults);
  }
  
  
  
  #define next_ci(L)  (L->ci->next ? L->ci->next : luaE_extendCI(L))
  
  
  /*
  ** Prepare a function for a tail call, building its call info on top
  ** of the current call info. 'narg1' is the number of arguments plus 1
  ** (so that it includes the function itself).
  */
  void luaD_pretailcall (lua_State *L, CallInfo *ci, StkId func, int narg1) {
    Proto *p = clLvalue(s2v(func))->p;
    int fsize = p->maxstacksize;  /* frame size */
    int nfixparams = p->numparams;
    int i;
    for (i = 0; i < narg1; i++)  /* move down function and arguments */
      setobjs2s(L, ci->func + i, func + i);
    checkstackGC(L, fsize);
    func = ci->func;  /* moved-down function */
    for (; narg1 <= nfixparams; narg1++)
      setnilvalue(s2v(func + narg1));  /* complete missing arguments */
    ci->top = func + 1 + fsize;  /* top for new function */
    lua_assert(ci->top <= L->stack_last);
    ci->u.l.savedpc = p->code;  /* starting point */
    ci->callstatus |= CIST_TAIL;
    L->top = func + narg1;  /* set top */
  }
  
  
  /*
  ** 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) {
    lua_CFunction f;
   retry:
    switch (ttypetag(s2v(func))) {
      case LUA_VCCL:  /* C closure */
        f = clCvalue(s2v(func))->f;
        goto Cfunc;
      case LUA_VLCF:  /* light C function */
        f = fvalue(s2v(func));
       Cfunc: {
        int n;  /* number of returns */
        CallInfo *ci;
        checkstackGCp(L, LUA_MINSTACK, func);  /* ensure minimum stack size */
        L->ci = ci = next_ci(L);
        ci->nresults = nresults;
        ci->callstatus = CIST_C;
        ci->top = L->top + LUA_MINSTACK;
        ci->func = func;
        lua_assert(ci->top <= L->stack_last);
        if (L->hookmask & LUA_MASKCALL) {
          int narg = cast_int(L->top - func) - 1;
          luaD_hook(L, LUA_HOOKCALL, -1, 1, narg);
        }
        lua_unlock(L);
        n = (*f)(L);  /* do the actual call */
        lua_lock(L);
        api_checknelems(L, n);
        luaD_poscall(L, ci, n);
        break;
      }
      case LUA_VLCL: {  /* Lua function */
        CallInfo *ci;
        Proto *p = clLvalue(s2v(func))->p;
        int narg = cast_int(L->top - func) - 1;  /* number of real arguments */
        int nfixparams = p->numparams;
        int fsize = p->maxstacksize;  /* frame size */
        checkstackGCp(L, fsize, func);
        L->ci = ci = next_ci(L);
        ci->nresults = nresults;
        ci->u.l.savedpc = p->code;  /* starting point */
        ci->callstatus = 0;
        ci->top = func + 1 + fsize;
        ci->func = func;
        L->ci = ci;
        for (; narg < nfixparams; narg++)
          setnilvalue(s2v(L->top++));  /* complete missing arguments */
        lua_assert(ci->top <= L->stack_last);
        luaV_execute(L, ci);  /* run the function */
        break;
      }
      default: {  /* not a function */
        checkstackGCp(L, 1, func);  /* space for metamethod */
        luaD_tryfuncTM(L, func);  /* try to get '__call' metamethod */
        goto retry;  /* try again with metamethod */
      }
    }
  }
  
  
  /*
  ** Similar to 'luaD_call', but does not allow yields during the call.
  */
  void luaD_callnoyield (lua_State *L, StkId func, int nResults) {
    incXCcalls(L);
    if (getCcalls(L) <= CSTACKERR) {  /* possible C stack overflow? */
      luaE_exitCcall(L);  /* to compensate decrement in next call */
      luaE_enterCcall(L);  /* check properly */
    }
    luaD_call(L, func, nResults);
    decXCcalls(L);
  }
  
  
  /*
  ** 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 && yieldable(L));
    /* 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, n);  /* finish 'luaD_call' */
  }
  
  
  /*
  ** 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) {
    CallInfo *ci;
    if (ud != NULL)  /* error status? */
      finishCcall(L, *(int *)ud);  /* finish 'lua_pcallk' callee */
    while ((ci = L->ci) != &L->base_ci) {  /* something in the stack */
      if (!isLua(ci))  /* C function? */
        finishCcall(L, LUA_YIELD);  /* complete its execution */
      else {  /* Lua function */
        luaV_finishOp(L);  /* finish interrupted instruction */
        luaV_execute(L, ci);  /* 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->u2.funcidx);
    luaF_close(L, oldtop, status);  /* may change the stack */
    oldtop = restorestack(L, ci->u2.funcidx);
    luaD_seterrorobj(L, status, oldtop);
    L->ci = ci;
    L->allowhook = getoah(ci->callstatus);  /* restore original 'allowhook' */
    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? */
      luaD_call(L, firstArg - 1, LUA_MULTRET);
    }
    else {  /* resuming from previous yield */
      lua_assert(L->status == LUA_YIELD);
      L->status = LUA_OK;  /* mark that it is running (again) */
      if (isLua(ci))  /* yielded inside a hook? */
        luaV_execute(L, ci);  /* 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);
        }
        luaD_poscall(L, ci, n);  /* finish 'luaD_call' */
      }
      unroll(L, NULL);  /* run continuation */
    }
  }
  
  LUA_API int lua_resume (lua_State *L, lua_State *from, int nargs,
                                        int *nresults) {
    int status;
    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->top - (L->ci->func + 1) == nargs)  /* no function? */
        return resume_error(L, "cannot resume dead coroutine", nargs);
    }
    else if (L->status != LUA_YIELD)  /* ended with errors? */
      return resume_error(L, "cannot resume dead coroutine", nargs);
    if (from == NULL)
      L->nCcalls = CSTACKTHREAD;
    else  /* correct 'nCcalls' for this thread */
      L->nCcalls = getCcalls(from) - L->nci - CSTACKCF;
    if (L->nCcalls <= CSTACKERR)
      return resume_error(L, "C stack overflow", nargs);
    luai_userstateresume(L, nargs);
    api_checknelems(L, (L->status == LUA_OK) ? nargs + 1 : nargs);
    status = luaD_rawrunprotected(L, resume, &nargs);
     /* continue running after recoverable errors */
    while (errorstatus(status) && recover(L, status)) {
      /* unroll continuation */
      status = luaD_rawrunprotected(L, unroll, &status);
    }
    if (likely(!errorstatus(status)))
      lua_assert(status == L->status);  /* normal end or yield */
    else {  /* unrecoverable error */
      L->status = cast_byte(status);  /* mark thread as 'dead' */
      luaD_seterrorobj(L, status, L->top);  /* push error message */
      L->ci->top = L->top;
    }
    *nresults = (status == LUA_YIELD) ? L->ci->u2.nyield
                                      : cast_int(L->top - (L->ci->func + 1));
    lua_unlock(L);
    return status;
  }
  
  
  LUA_API int lua_isyieldable (lua_State *L) {
    return yieldable(L);
  }
  
  
  LUA_API int lua_yieldk (lua_State *L, int nresults, lua_KContext ctx,
                          lua_KFunction k) {
    CallInfo *ci;
    luai_userstateyield(L, nresults);
    lua_lock(L);
    ci = L->ci;
    api_checknelems(L, nresults);
    if (unlikely(!yieldable(L))) {
      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;
    if (isLua(ci)) {  /* inside a hook? */
      lua_assert(!isLuacode(ci));
      api_check(L, k == NULL, "hooks cannot continue after yielding");
      ci->u2.nyield = 0;  /* no results */
    }
    else {
      if ((ci->u.c.k = k) != NULL)  /* is there a continuation? */
        ci->u.c.ctx = ctx;  /* save context */
      ci->u2.nyield = nresults;  /* save number of 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' */
  }
  
  
  /*
  ** Call the C function 'func' in protected mode, restoring basic
  ** thread information ('allowhook', etc.) and in particular
  ** its stack level in case of errors.
  */
  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;
    ptrdiff_t old_errfunc = L->errfunc;
    L->errfunc = ef;
    status = luaD_rawrunprotected(L, func, u);
    if (unlikely(status != LUA_OK)) {  /* an error occurred? */
      StkId oldtop = restorestack(L, old_top);
      L->ci = old_ci;
      L->allowhook = old_allowhooks;
      status = luaF_close(L, oldtop, status);
      oldtop = restorestack(L, old_top);  /* previous call may change stack */
      luaD_seterrorobj(L, status, oldtop);
      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;
    incnny(L);  /* 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);
    decnny(L);
    return status;
  }
  
  
  