Re: math.random() when lua_Number is int

[Lisa Parratt <lisa@...>]

Lisa Parratt wrote:
> I vaguely remember having got around this problem  in a manner that  
> works with both reals and integers - I'll look it up when I get to work.

This is the version I'm using, based on the Lua 5.0 random function:

static int math_random (lua_State *L) {
   /* the `%' avoids the (rare) case of r==1, and is needed also because on
      some systems (SunOS!) `rand()' may return a value larger than 
RAND_MAX */
   lua_Number r = (lua_Number)(rand()%RAND_MAX);
   switch (lua_gettop(L)) {  /* check number of arguments */
     case 0: {  /* no arguments */
       lua_pushnumber(L, (lua_Number)(((int)r) / RAND_MAX));  /* Number 
between 0 and 1 */
       break;
     }
     case 1: {  /* only upper limit */
       int u = luaL_checkint(L, 1);
       luaL_argcheck(L, 1<=u, 1, "interval is empty");
       lua_pushnumber(L, (lua_Number)((int)(((int)r) / (int)((RAND_MAX 
/ (u-1))))+1));  /* int between 1 and `u' */
       break;
     }
     case 2: {  /* lower and upper limits */
       int l = luaL_checkint(L, 1);
       int u = luaL_checkint(L, 2);
       luaL_argcheck(L, l<=u, 2, "interval is empty");
       lua_pushnumber(L, (lua_Number)((int)(((int)r) / (int)((RAND_MAX 
/ (u-l))))+l));  /* int between 'l' and `u' */
       break;
     }
     default: return luaL_error(L, "wrong number of arguments");
   }
   return 1;
 }


--
Lisa
http://www.thecommune.org.uk/~lisa/