rusefi
/
lua
mirror of https://github.com/rusefi/lua.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

'math.random(n,m)' interval restricted in size, to avoid using conversion 

between 'double' and 'unsigned' (which can be slow and unreliable)
This commit is contained in:
Roberto Ierusalimschy 2014-04-17 13:09:40 -03:00
parent 0172c9552c
commit cbe4998bc2
1 changed files with 12 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
lmathlib.c
View File

@ -1,5 +1,5 @@
/*
** $Id: lmathlib.c,v 1.95 2014/04/03 14:18:19 roberto Exp roberto $
** $Id: lmathlib.c,v 1.97 2014/04/10 17:53:33 roberto Exp roberto $
** Standard mathematical library
** See Copyright Notice in lua.h
*/
@ -228,12 +228,14 @@ static int math_max (lua_State *L) {
return 1;
}
/*
** This function uses 'double' (instead of 'lua_Number') to ensure that
** all bits from 'l_rand' can be represented, and that 'RAND_MAX + 1.0'
** will keep full precision (ensuring that 'r' is always less than 1.0.)
*/
static int math_random (lua_State *L) {
lua_Integer low, up;
lua_Number r = (lua_Number)l_rand() * (1.0 / ((lua_Number)RAND_MAX + 1.0));
if (r >= 1.0) /* can occur if lua_Number has no precision for RAND_MAX */
r = 0.0; /* statistically irrelevant; avoids out-of-range results */
double r = (double)l_rand() * (1.0 / ((double)RAND_MAX + 1.0));
switch (lua_gettop(L)) { /* check number of arguments */
case 0: { /* no arguments */
lua_pushnumber(L, r); /* Number between 0 and 1 */
@ -252,9 +254,11 @@ static int math_random (lua_State *L) {
default: return luaL_error(L, "wrong number of arguments");
}
/* random integer in the interval [low, up] */
luaL_argcheck(L, low <= up, 1, "interval is empty");
r *= ((lua_Number)((lua_Unsigned)up - (lua_Unsigned)low) + 1.0);
lua_pushinteger(L, (lua_Integer)((lua_Unsigned)r + (lua_Unsigned)low));
luaL_argcheck(L, low <= up, 1, "interval is empty");
luaL_argcheck(L, (lua_Unsigned)up - low <= (lua_Unsigned)LUA_MAXINTEGER,
1, "interval too large");
r *= (double)(up - low) + 1.0;
lua_pushinteger(L, (lua_Integer)r + low);
return 1;
}