Re: lua_number2integer

[Asko Kauppi <askok@...>]

'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."
     */
#ifdef LUA_COMPAT_TOINTEGER
	...
#else
  /* 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;
  }
#endif
  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));
#else
  return tonumber(o,&tmp) && tt_integer_valued(o,&dum);
#endif
}

-asko


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
> > process:
> >
> >   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: http://www.inf.puc-rio.br/~roberto/struct/
>
> --Mike