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/* ----------------------------------------------------------------------- *
*
* 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 */
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