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'lua_tointeger()' could easily be changed so that it does not allow non-integer numbers as input.

The LNUM patch actually does this, unless LUA_COMPAT_TOINTEGER is defined.

LUA_API lua_Integer lua_tointeger (lua_State *L, int idx) {
  TValue n;
/* Lua 5.1 documented behaviour is to return nonzero for non- integer: * "If the number is not an integer, it is truncated in some non- specified way."
  /* New suggestion */
  const TValue *o = index2adr(L, idx);
  if (tonumber(o, &n)) {
    lua_Integer i;
    if (ttisint(o)) return ivalue(o);
    if (tt_integer_valued(o,&i)) return i;
  return 0;

Also, a 'lua_isinteger()' would be needed to tell, if a value can be carried unchanged in 'lua_Integer'.

LUA_API int lua_isinteger (lua_State *L, int idx) {
  TValue tmp;
  lua_Integer dum;
  const TValue *o = index2adr(L, idx);
#ifdef LUA_TINT
  return tonumber(o,&tmp) && (ttisint(o) || tt_integer_valued(o,&dum));
  return tonumber(o,&tmp) && tt_integer_valued(o,&dum);


Mike Pall kirjoitti 25.9.2008 kello 15:56:

Cuero Bugot wrote:
Here is the code which revealed the unconsistency of the number to integer

  string.char(112+remaining/256, remaining%256)

where remaining was taken from 0 to 4095.

This code was done assuming that the string.char function was "correctly
truncating" the value as C would do it in such a case.

Passing non-integral numbers to library functions expecting
integral numbers is "undefined". There is no "correct rounding
mode" in this case -- Lua is not C.

Rewrite your example as:

 local r = remaining % 256
 string.char(112 + (remaining-r)/256, r)

Or better use the struct library:

 struct.pack(">H", 0x7000+remaining)

Get it from: