memcmplen.h

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//
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
 
#ifndef LZMA_MEMCMPLEN_H
#define LZMA_MEMCMPLEN_H
 
#include "common.h"
 
#ifdef HAVE_IMMINTRIN_H
#   include <immintrin.h>
#endif
 
 
static inline uint32_t lzma_attribute((__always_inline__))
lzma_memcmplen(const uint8_t *buf1, const uint8_t *buf2,
        uint32_t len, uint32_t limit)
{
    assert(len <= limit);
    assert(limit <= UINT32_MAX / 2);
 
#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
        && ((TUKLIB_GNUC_REQ(3, 4) && defined(__x86_64__)) \
            || (defined(__INTEL_COMPILER) && defined(__x86_64__)) \
            || (defined(__INTEL_COMPILER) && defined(_M_X64)) \
            || (defined(_MSC_VER) && defined(_M_X64)))
    // NOTE: This will use 64-bit unaligned access which
    // TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit, but
    // it's convenient here at least as long as it's x86-64 only.
    //
    // I keep this x86-64 only for now since that's where I know this
    // to be a good method. This may be fine on other 64-bit CPUs too.
    // On big endian one should use xor instead of subtraction and switch
    // to __builtin_clzll().
#define LZMA_MEMCMPLEN_EXTRA 8
    while (len < limit) {
        const uint64_t x = read64ne(buf1 + len) - read64ne(buf2 + len);
        if (x != 0) {
#   if defined(_M_X64) // MSVC or Intel C compiler on Windows
            unsigned long tmp;
            _BitScanForward64(&tmp, x);
            len += (uint32_t)tmp >> 3;
#   else // GCC, clang, or Intel C compiler
            len += (uint32_t)__builtin_ctzll(x) >> 3;
#   endif
            return my_min(len, limit);
        }
 
        len += 8;
    }
 
    return limit;
 
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
        && defined(HAVE__MM_MOVEMASK_EPI8) \
        && ((defined(__GNUC__) && defined(__SSE2_MATH__)) \
            || (defined(__INTEL_COMPILER) && defined(__SSE2__)) \
            || (defined(_MSC_VER) && defined(_M_IX86_FP) \
                && _M_IX86_FP >= 2))
    // NOTE: Like above, this will use 128-bit unaligned access which
    // TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit.
    //
    // SSE2 version for 32-bit and 64-bit x86. On x86-64 the above
    // version is sometimes significantly faster and sometimes
    // slightly slower than this SSE2 version, so this SSE2
    // version isn't used on x86-64.
#   define LZMA_MEMCMPLEN_EXTRA 16
    while (len < limit) {
        const uint32_t x = 0xFFFF ^ _mm_movemask_epi8(_mm_cmpeq_epi8(
            _mm_loadu_si128((const __m128i *)(buf1 + len)),
            _mm_loadu_si128((const __m128i *)(buf2 + len))));
 
        if (x != 0) {
            len += ctz32(x);
            return my_min(len, limit);
        }
 
        len += 16;
    }
 
    return limit;
 
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && !defined(WORDS_BIGENDIAN)
    // Generic 32-bit little endian method
#   define LZMA_MEMCMPLEN_EXTRA 4
    while (len < limit) {
        uint32_t x = read32ne(buf1 + len) - read32ne(buf2 + len);
        if (x != 0) {
            if ((x & 0xFFFF) == 0) {
                len += 2;
                x >>= 16;
            }
 
            if ((x & 0xFF) == 0)
                ++len;
 
            return my_min(len, limit);
        }
 
        len += 4;
    }
 
    return limit;
 
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && defined(WORDS_BIGENDIAN)
    // Generic 32-bit big endian method
#   define LZMA_MEMCMPLEN_EXTRA 4
    while (len < limit) {
        uint32_t x = read32ne(buf1 + len) ^ read32ne(buf2 + len);
        if (x != 0) {
            if ((x & 0xFFFF0000) == 0) {
                len += 2;
                x <<= 16;
            }
 
            if ((x & 0xFF000000) == 0)
                ++len;
 
            return my_min(len, limit);
        }
 
        len += 4;
    }
 
    return limit;
 
#else
    // Simple portable version that doesn't use unaligned access.
#   define LZMA_MEMCMPLEN_EXTRA 0
    while (len < limit && buf1[len] == buf2[len])
        ++len;
 
    return len;
#endif
}
 
#endif