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 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
