From 01b303c87e4b3d3c9daed6312658bb73638498a6 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Mon, 28 Apr 2003 10:30:14 -0300
Subject: simpler log2 implementation
---
lobject.c | 31 +++++++++++--------------------
1 file changed, 11 insertions(+), 20 deletions(-)
(limited to 'lobject.c')
diff --git a/lobject.c b/lobject.c
index 7106478a..26accff2 100644
--- a/lobject.c
+++ b/lobject.c
@@ -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,
+ 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,
- 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];
+
}
--
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