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