1 /* ----------------------------------------------------------------------- *
2 *
3 * Copyright 2010 Intel Corporation; author: H. Peter Anvin
4 *
5 * Permission is hereby granted, free of charge, to any person
6 * obtaining a copy of this software and associated documentation
7 * files (the "Software"), to deal in the Software without
8 * restriction, including without limitation the rights to use,
9 * copy, modify, merge, publish, distribute, sublicense, and/or
10 * sell copies of the Software, and to permit persons to whom
11 * the Software is furnished to do so, subject to the following
12 * conditions:
13 *
14 * The above copyright notice and this permission notice shall
15 * be included in all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
18 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
19 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
20 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
21 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
22 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
23 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
24 * OTHER DEALINGS IN THE SOFTWARE.
25 *
26 * ----------------------------------------------------------------------- */
27
28 #ifndef _ILOG2_H
29 #define _ILOG2_H
30
31 /*
32 * Computes floor(log2(x)) -- undefined for x = 0.
33 */
34
35 #include <klibc/compiler.h>
36 #include <stdint.h>
37
ilog2(uint32_t __v)38 static inline __constfunc uint32_t ilog2(uint32_t __v)
39 {
40 # if __GNUC__ >= 4
41 return __builtin_clz(__v) ^ 31;
42 # else
43 asm("bsrl %1,%0" : "=r" (__v) : "rm" (__v));
44 return __v;
45 # endif
46 }
47
48 #endif /* _ILOG2_H */
49