text: /*
  ** $Id: ltm.c,v 2.36 2015/11/03 15:47:30 roberto Exp $
  ** Tag methods
  ** See Copyright Notice in lua.h
  */
  
  #define ltm_cpp
  #define LUA_CORE
  
  #include "uvm/lprefix.h"
  
  
  #include <string.h>
  
  #include "uvm/lua.h"
  
  #include "uvm/ldebug.h"
  #include "uvm/ldo.h" 
  #include "uvm/lobject.h"
  #include "uvm/lstate.h"
  #include "uvm/lstring.h"
  #include "uvm/ltable.h"
  #include "uvm/ltm.h"
  #include "uvm/lvm.h"
  
  
  static const char udatatypename[] = "userdata";
  
  LUAI_DDEF const char *const luaT_typenames_[LUA_TOTALTAGS] = {
      "no value",
      "nil", "boolean", udatatypename, "number",
      "string", "table", "function", udatatypename, "thread",
      "proto" /* this last case is used for tests only */
  };
  
  
  void luaT_init(lua_State *L) {
      static const char *const luaT_eventname[] = {  /* ORDER TM */
          "__index", "__newindex",
          "__gc", "__mode", "__len", "__eq",
          "__add", "__sub", "__mul", "__mod", "__pow",
          "__div", "__idiv",
          "__band", "__bor", "__bxor", "__shl", "__shr",
          "__unm", "__bnot", "__lt", "__le",
          "__concat", "__call"
      };
      int i;
      for (i = 0; i < TM_N; i++) {
          L->tmname[i] = luaS_new(L, luaT_eventname[i]);
      }
  }
  
  
  /*
  ** function to be used with macro "fasttm": optimized for absence of
  ** tag methods
  */
  const TValue *luaT_gettm(uvm_types::GcTable *events, TMS event, uvm_types::GcString *ename) {
      const TValue *tm = luaH_getstr(events, ename);
      lua_assert(event <= TM_EQ);
      if (ttisnil(tm)) {  /* no tag method? */
  		events->flags |= cast_byte(1u << event);  /* cache this fact */
          return nullptr;
      }
      else return tm;
  }
  
  
  const TValue *luaT_gettmbyobj(lua_State *L, const TValue *o, TMS event) {
      uvm_types::GcTable *mt;
      switch (ttnov(o)) {
      case LUA_TTABLE:
          mt = hvalue(o)->metatable;
          break;
      case LUA_TUSERDATA:
          mt = uvalue(o)->metatable;
          break;
      default:
          mt = L->mt[ttnov(o)];
      }
      return (mt ? luaH_getshortstr(mt, L->tmname[event]) : luaO_nilobject);
  }
  
  
  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);
      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;
      if (!hasres)  /* no result? 'p3' is third argument */
          setobj2s(L, L->top++, p3);  /* 3rd argument */
      /* metamethod may yield only when called from Lua code */
      if (isLua(L->ci))
          luaD_call(L, func, hasres);
      else
          luaD_callnoyield(L, func, hasres);
      if (hasres) {  /* if has result, move it to its place */
          p3 = restorestack(L, result);
          setobjs2s(L, p3, --L->top);
      }
  }
  
  
  int luaT_callbinTM(lua_State *L, const TValue *p1, const TValue *p2,
      StkId res, TMS event) {
      const TValue *tm = luaT_gettmbyobj(L, p1, event);  /* try first operand */
      if (ttisnil(tm))
          tm = luaT_gettmbyobj(L, p2, event);  /* try second operand */
      if (ttisnil(tm)) return 0;
      luaT_callTM(L, tm, p1, p2, res, 1);
      return 1;
  }
  
  
  void luaT_trybinTM(lua_State *L, const TValue *p1, const TValue *p2,
      StkId res, TMS event) {
      if (!luaT_callbinTM(L, p1, p2, res, event)) {
          switch (event) {
          case TM_CONCAT:
              luaG_concaterror(L, p1, p2);
              /* call never returns, but to avoid warnings: *//* FALLTHROUGH */
          case TM_BAND: case TM_BOR: case TM_BXOR:
          case TM_SHL: case TM_SHR: case TM_BNOT: {
              lua_Number dummy;
              if (tonumber(p1, &dummy) && tonumber(p2, &dummy))
                  luaG_tointerror(L, p1, p2);
              else
                  luaG_opinterror(L, p1, p2, "perform bitwise operation on");
          }
                       /* calls never return, but to avoid warnings: *//* FALLTHROUGH */
          default:
              luaG_opinterror(L, p1, p2, "perform arithmetic on");
          }
      }
  }
  
  
  int luaT_callorderTM(lua_State *L, const TValue *p1, const TValue *p2,
      TMS event) {
      if (!luaT_callbinTM(L, p1, p2, L->top, event))
          return -1;  /* no metamethod */
      else
          return !l_isfalse(L->top);
  }
  
  