mirror of https://git.tukaani.org/xz.git
61 lines
1.1 KiB
C
61 lines
1.1 KiB
C
///////////////////////////////////////////////////////////////////////////////
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//
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/// \file bsr.h
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/// \brief Bit scan reverse
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//
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// Author: Lasse Collin
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//
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// This file has been put into the public domain.
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// You can do whatever you want with this file.
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//
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///////////////////////////////////////////////////////////////////////////////
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#ifndef LZMA_BSR_H
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#define LZMA_BSR_H
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// NOTE: Both input and output variables for lzma_bsr must be uint32_t.
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#if defined(__GNUC__) && (defined (HAVE_ASM_X86) || defined(HAVE_ASM_X86_64))
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# define lzma_bsr(dest, n) \
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__asm__("bsrl %1, %0" : "=r" (dest) : "rm" (n))
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#else
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# define lzma_bsr(dest, n) dest = lzma_bsr_helper(n)
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static inline uint32_t
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lzma_bsr_helper(uint32_t n)
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{
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assert(n != 0);
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uint32_t i = 31;
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if ((n & UINT32_C(0xFFFF0000)) == 0) {
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n <<= 16;
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i = 15;
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}
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if ((n & UINT32_C(0xFF000000)) == 0) {
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n <<= 8;
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i -= 8;
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}
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if ((n & UINT32_C(0xF0000000)) == 0) {
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n <<= 4;
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i -= 4;
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}
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if ((n & UINT32_C(0xC0000000)) == 0) {
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n <<= 2;
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i -= 2;
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}
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if ((n & UINT32_C(0x80000000)) == 0)
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--i;
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return i;
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}
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#endif
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#endif
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