"legal" way to convert a float to an integer in C

lvm.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lvm.c,v 2.169 2013/05/06 17:17:09 roberto Exp roberto $
+** $Id: lvm.c,v 2.170 2013/05/26 14:47:51 roberto Exp roberto $
 ** Lua virtual machine
 ** See Copyright Notice in lua.h
 */
@@ -58,17 +58,25 @@ int luaV_tostring (lua_State *L, StkId obj) {
 }
 
 
+/*
+** Check whether a float number is within the range of a lua_Integer.
+** (The comparisons are tricky because of rounding, which can or
+** not occur depending on the relative sizes of floats and integers.)
+** This function is called only when 'n' has an integer value.
+*/
 int luaV_numtointeger (lua_Number n, lua_Integer *p) {
-  lua_Integer k;
-  lua_number2integer(k, n);
-  if (luai_numeq(cast_num(k), n)) {  /* 'k' is int? */
-    *p = k;
+  if (cast_num(MIN_INTEGER) <= n && n < (MAX_INTEGER + cast_num(1))) {
+    *p = cast_integer(n);
+    lua_assert(cast_num(*p) == n);
     return 1;
   }
-  return 0;
+  return 0;  /* number is outside integer limits */
 }
 
 
+/*
+** try to convert a non-integer value to an integer
+*/
 int luaV_tointeger_ (const TValue *obj, lua_Integer *p) {
   lua_Number n;
   lua_assert(!ttisinteger(obj));