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simpler log2 implementation

This commit is contained in:
Roberto Ierusalimschy 2003-04-28 10:30:14 -03:00
parent 762c737037
commit 01b303c87e
1 changed files with 11 additions and 20 deletions
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31
lobject.c
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@ -1,5 +1,5 @@
/*
** $Id: lobject.c,v 1.96 2003/02/18 16:02:56 roberto Exp roberto $
** $Id: lobject.c,v 1.97 2003/04/03 13:35:34 roberto Exp roberto $
** Some generic functions over Lua objects
** See Copyright Notice in lua.h
*/
@ -45,29 +45,20 @@ int luaO_int2fb (unsigned int x) {
int luaO_log2 (unsigned int x) {
static const lu_byte log_8[255] = {
0,
1,1,
2,2,2,2,
3,3,3,3,3,3,3,3,
4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
static const lu_byte log_2[256] = {
0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8
};
if (x >= 0x00010000) {
if (x >= 0x01000000) return log_8[((x>>24) & 0xff) - 1]+24;
else return log_8[((x>>16) & 0xff) - 1]+16;
}
else {
if (x >= 0x00000100) return log_8[((x>>8) & 0xff) - 1]+8;
else if (x) return log_8[(x & 0xff) - 1];
return -1; /* special `log' for 0 */
}
int l = -1;
while (x >= 256) { l += 8; x >>= 8; }
return l + log_2[x];
}