1 /////////////////////////////////////////////////////////////////////////////// 2 // 3 /// \file memcmplen.h 4 /// \brief Optimized comparison of two buffers 5 // 6 // Author: Lasse Collin 7 // 8 // This file has been put into the public domain. 9 // You can do whatever you want with this file. 10 // 11 /////////////////////////////////////////////////////////////////////////////// 12 13 #ifndef LZMA_MEMCMPLEN_H 14 #define LZMA_MEMCMPLEN_H 15 16 #include "common.h" 17 18 #ifdef HAVE_IMMINTRIN_H 19 # include <immintrin.h> 20 #endif 21 22 23 /// Find out how many equal bytes the two buffers have. 24 /// 25 /// \param buf1 First buffer 26 /// \param buf2 Second buffer 27 /// \param len How many bytes have already been compared and will 28 /// be assumed to match 29 /// \param limit How many bytes to compare at most, including the 30 /// already-compared bytes. This must be significantly 31 /// smaller than UINT32_MAX to avoid integer overflows. 32 /// Up to LZMA_MEMCMPLEN_EXTRA bytes may be read past 33 /// the specified limit from both buf1 and buf2. 34 /// 35 /// \return Number of equal bytes in the buffers is returned. 36 /// This is always at least len and at most limit. 37 /// 38 /// \note LZMA_MEMCMPLEN_EXTRA defines how many extra bytes may be read. 39 /// It's rounded up to 2^n. This extra amount needs to be 40 /// allocated in the buffers being used. It needs to be 41 /// initialized too to keep Valgrind quiet. 42 static inline uint32_t lzma_attribute((__always_inline__)) 43 lzma_memcmplen(const uint8_t *buf1, const uint8_t *buf2, 44 uint32_t len, uint32_t limit) 45 { 46 assert(len <= limit); 47 assert(limit <= UINT32_MAX / 2); 48 49 #if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ 50 && ((TUKLIB_GNUC_REQ(3, 4) && defined(__x86_64__)) \ 51 || (defined(__INTEL_COMPILER) && defined(__x86_64__)) \ 52 || (defined(__INTEL_COMPILER) && defined(_M_X64)) \ 53 || (defined(_MSC_VER) && defined(_M_X64))) 54 // NOTE: This will use 64-bit unaligned access which 55 // TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit, but 56 // it's convenient here at least as long as it's x86-64 only. 57 // 58 // I keep this x86-64 only for now since that's where I know this 59 // to be a good method. This may be fine on other 64-bit CPUs too. 60 // On big endian one should use xor instead of subtraction and switch 61 // to __builtin_clzll(). 62 #define LZMA_MEMCMPLEN_EXTRA 8 63 while (len < limit) { 64 const uint64_t x = *(const uint64_t *)(buf1 + len) 65 - *(const uint64_t *)(buf2 + len); 66 if (x != 0) { 67 # if defined(_M_X64) // MSVC or Intel C compiler on Windows 68 unsigned long tmp; 69 _BitScanForward64(&tmp, x); 70 len += (uint32_t)tmp >> 3; 71 # else // GCC, clang, or Intel C compiler 72 len += (uint32_t)__builtin_ctzll(x) >> 3; 73 # endif 74 return my_min(len, limit); 75 } 76 77 len += 8; 78 } 79 80 return limit; 81 82 #elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) \ 83 && defined(HAVE__MM_MOVEMASK_EPI8) \ 84 && ((defined(__GNUC__) && defined(__SSE2_MATH__)) \ 85 || (defined(__INTEL_COMPILER) && defined(__SSE2__)) \ 86 || (defined(_MSC_VER) && defined(_M_IX86_FP) \ 87 && _M_IX86_FP >= 2)) 88 // NOTE: Like above, this will use 128-bit unaligned access which 89 // TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit. 90 // 91 // SSE2 version for 32-bit and 64-bit x86. On x86-64 the above 92 // version is sometimes significantly faster and sometimes 93 // slightly slower than this SSE2 version, so this SSE2 94 // version isn't used on x86-64. 95 # define LZMA_MEMCMPLEN_EXTRA 16 96 while (len < limit) { 97 const uint32_t x = 0xFFFF ^ _mm_movemask_epi8(_mm_cmpeq_epi8( 98 _mm_loadu_si128((const __m128i *)(buf1 + len)), 99 _mm_loadu_si128((const __m128i *)(buf2 + len)))); 100 101 if (x != 0) { 102 # if defined(__INTEL_COMPILER) 103 len += _bit_scan_forward(x); 104 # elif defined(_MSC_VER) 105 unsigned long tmp; 106 _BitScanForward(&tmp, x); 107 len += tmp; 108 # else 109 len += __builtin_ctz(x); 110 # endif 111 return my_min(len, limit); 112 } 113 114 len += 16; 115 } 116 117 return limit; 118 119 #elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && !defined(WORDS_BIGENDIAN) 120 // Generic 32-bit little endian method 121 # define LZMA_MEMCMPLEN_EXTRA 4 122 while (len < limit) { 123 uint32_t x = *(const uint32_t *)(buf1 + len) 124 - *(const uint32_t *)(buf2 + len); 125 if (x != 0) { 126 if ((x & 0xFFFF) == 0) { 127 len += 2; 128 x >>= 16; 129 } 130 131 if ((x & 0xFF) == 0) 132 ++len; 133 134 return my_min(len, limit); 135 } 136 137 len += 4; 138 } 139 140 return limit; 141 142 #elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && defined(WORDS_BIGENDIAN) 143 // Generic 32-bit big endian method 144 # define LZMA_MEMCMPLEN_EXTRA 4 145 while (len < limit) { 146 uint32_t x = *(const uint32_t *)(buf1 + len) 147 ^ *(const uint32_t *)(buf2 + len); 148 if (x != 0) { 149 if ((x & 0xFFFF0000) == 0) { 150 len += 2; 151 x <<= 16; 152 } 153 154 if ((x & 0xFF000000) == 0) 155 ++len; 156 157 return my_min(len, limit); 158 } 159 160 len += 4; 161 } 162 163 return limit; 164 165 #else 166 // Simple portable version that doesn't use unaligned access. 167 # define LZMA_MEMCMPLEN_EXTRA 0 168 while (len < limit && buf1[len] == buf2[len]) 169 ++len; 170 171 return len; 172 #endif 173 } 174 175 #endif 176