| /* ----------------------------------------------------------------------- * |
| * |
| * Copyright 2010 Intel Corporation; author: H. Peter Anvin |
| * |
| * Permission is hereby granted, free of charge, to any person |
| * obtaining a copy of this software and associated documentation |
| * files (the "Software"), to deal in the Software without |
| * restriction, including without limitation the rights to use, |
| * copy, modify, merge, publish, distribute, sublicense, and/or |
| * sell copies of the Software, and to permit persons to whom |
| * the Software is furnished to do so, subject to the following |
| * conditions: |
| * |
| * The above copyright notice and this permission notice shall |
| * be included in all copies or substantial portions of the Software. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, |
| * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES |
| * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND |
| * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT |
| * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, |
| * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING |
| * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR |
| * OTHER DEALINGS IN THE SOFTWARE. |
| * |
| * ----------------------------------------------------------------------- */ |
| |
| #ifndef _ILOG2_H |
| #define _ILOG2_H |
| |
| /* |
| * Computes floor(log2(x)) -- undefined for x = 0. |
| */ |
| |
| #include <klibc/compiler.h> |
| #include <stdint.h> |
| |
| static inline __constfunc uint32_t ilog2(uint32_t __v) |
| { |
| # if __GNUC__ >= 4 |
| return __builtin_clz(__v) ^ 31; |
| # else |
| asm("bsrl %1,%0" : "=r" (__v) : "rm" (__v)); |
| return __v; |
| # endif |
| } |
| |
| #endif /* _ILOG2_H */ |