75 lines
1.4 KiB
C
75 lines
1.4 KiB
C
/*! \file
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* \brief log2comp.h - various base 2 log computation versions
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*
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* Asterisk -- A telephony toolkit for Linux.
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*
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* \author Alex Volkov <codepro@usa.net>
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*
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* Copyright (c) 2004 - 2005, Digium Inc.
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License
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*
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* Define WANT_ASM before including this file to use assembly
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* whenever possible
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*/
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#if defined(_MSC_VER)
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# define inline __inline
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#elif defined(__GNUC__)
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# define inline __inline__
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#else
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# define inline
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#endif
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#if defined(WANT_ASM) && defined(_MSC_VER) && defined(_M_IX86)
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/* MS C Inline Asm */
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# pragma warning( disable : 4035 )
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static inline int ilog2(int val) { __asm
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{
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xor eax, eax
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dec eax
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bsr eax, val
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}}
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# pragma warning( default : 4035 )
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#elif defined(WANT_ASM) && defined(__GNUC__) && (defined(__i386__) || defined(i386))
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/* GNU Inline Asm */
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static inline int ilog2(int val)
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{
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int a;
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__asm__
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("\
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xorl %0, %0 ;\
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decl %0 ;\
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bsrl %1, %0 ;\
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"
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: "=&r" (a)
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: "mr" (val)
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: "cc"
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);
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return a;
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}
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#elif defined(WANT_ASM) && defined(__GNUC__) && defined(__powerpc__)
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static inline int ilog2(int val)
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{
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int a;
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__asm__ ("cntlzw %0,%1"
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: "=r" (a)
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: "r" (val)
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);
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return 31-a;
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}
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#else
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/* no ASM for this compiler and/or platform */
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/* rather slow base 2 log computation
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* Using looped shift.
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*/
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static inline int ilog2(int val)
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{
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int i;
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for (i = -1; val; ++i, val >>= 1)
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;
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return (i);
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}
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#endif
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