simpler log2 implementation

author: Roberto Ierusalimschy <roberto@inf.puc-rio.br> 2003-04-28 10:30:14 -0300
committer: Roberto Ierusalimschy <roberto@inf.puc-rio.br> 2003-04-28 10:30:14 -0300
commit: 01b303c87e4b3d3c9daed6312658bb73638498a6 (patch)
tree: 53fb6d2bf92795333ca5501501094667ede0f6d4
parent: 762c7370376dbd13cd8aeb4d8c8da0bb153269c3 (diff)
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1 files changed, 11 insertions, 20 deletions
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] = {
+  static const lu_byte log_2[256] = {
-    0,
+    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,
-    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,
-    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) {
+  int l = -1;
-    if (x >= 0x01000000) return log_8[((x>>24) & 0xff) - 1]+24;
+  while (x >= 256) { l += 8; x >>= 8; }
-    else return log_8[((x>>16) & 0xff) - 1]+16;
+  return l + log_2[x];
-  }
-  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 */
-  }
 }
author	Roberto Ierusalimschy <roberto@inf.puc-rio.br>	2003-04-28 10:30:14 -0300
committer	Roberto Ierusalimschy <roberto@inf.puc-rio.br>	2003-04-28 10:30:14 -0300
commit	01b303c87e4b3d3c9daed6312658bb73638498a6 (patch)
tree	53fb6d2bf92795333ca5501501094667ede0f6d4
parent	762c7370376dbd13cd8aeb4d8c8da0bb153269c3 (diff)
download	lua-01b303c87e4b3d3c9daed6312658bb73638498a6.tar.gz lua-01b303c87e4b3d3c9daed6312658bb73638498a6.tar.bz2 lua-01b303c87e4b3d3c9daed6312658bb73638498a6.zip

diff --git a/lobject.c b/lobject.c index 7106478a..26accff2 100644 --- a/lobject.c +++ b/lobject.c
@@ -1,5 +1,5 @@
1	/*	1	/*
2	** $Id: lobject.c,v 1.96 2003/02/18 16:02:56 roberto Exp roberto $	2	** $Id: lobject.c,v 1.97 2003/04/03 13:35:34 roberto Exp roberto $
3	** Some generic functions over Lua objects	3	** Some generic functions over Lua objects
4	** See Copyright Notice in lua.h	4	** See Copyright Notice in lua.h
5	*/	5	*/
@@ -45,29 +45,20 @@ int luaO_int2fb (unsigned int x) {
45		45
46		46
47	int luaO_log2 (unsigned int x) {	47	int luaO_log2 (unsigned int x) {
48	static const lu_byte log_8[255] = {	48	static const lu_byte log_2[256] = {
49	0,	49	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,
50	1,1,
51	2,2,2,2,
52	3,3,3,3,3,3,3,3,
53	4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
54	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,
55	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,	50	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,
56	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,
57	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,
58	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,	51	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,
59	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,	52	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,
60	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	53	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,
		54	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,
		55	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,
		56	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
61	};	57	};
62	if (x >= 0x00010000) {	58	int l = -1;
63	if (x >= 0x01000000) return log_8[((x>>24) & 0xff) - 1]+24;	59	while (x >= 256) { l += 8; x >>= 8; }
64	else return log_8[((x>>16) & 0xff) - 1]+16;	60	return l + log_2[x];
65	}	61
66	else {
67	if (x >= 0x00000100) return log_8[((x>>8) & 0xff) - 1]+8;
68	else if (x) return log_8[(x & 0xff) - 1];
69	return -1; /* special `log' for 0 */
70	}
71	}	62	}
72		63
73		64