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129 lines
3.4 KiB
129 lines
3.4 KiB
// Copyright 2016 The LevelDB Authors. All rights reserved. |
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// Use of this source code is governed by a BSD-style license that can be |
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// found in the LICENSE file. See the AUTHORS file for names of contributors. |
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// |
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// A portable implementation of crc32c, optimized to handle |
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// four bytes at a time. |
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// |
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// In a separate source file to allow this accelerated CRC32C function to be |
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// compiled with the appropriate compiler flags to enable x86 SSE 4.2 |
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// instructions. |
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#include <stdint.h> |
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#include <string.h> |
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#include "port/port.h" |
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#if defined(LEVELDB_PLATFORM_POSIX_SSE) |
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#if defined(_MSC_VER) |
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#include <intrin.h> |
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#elif defined(__GNUC__) && defined(__SSE4_2__) |
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#include <nmmintrin.h> |
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#include <cpuid.h> |
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#endif |
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#endif // defined(LEVELDB_PLATFORM_POSIX_SSE) |
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namespace leveldb { |
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namespace port { |
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#if defined(LEVELDB_PLATFORM_POSIX_SSE) |
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// Used to fetch a naturally-aligned 32-bit word in little endian byte-order |
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static inline uint32_t LE_LOAD32(const uint8_t *p) { |
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// SSE is x86 only, so ensured that |p| is always little-endian. |
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uint32_t word; |
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memcpy(&word, p, sizeof(word)); |
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return word; |
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} |
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#if defined(_M_X64) || defined(__x86_64__) // LE_LOAD64 is only used on x64. |
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// Used to fetch a naturally-aligned 64-bit word in little endian byte-order |
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static inline uint64_t LE_LOAD64(const uint8_t *p) { |
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uint64_t dword; |
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memcpy(&dword, p, sizeof(dword)); |
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return dword; |
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} |
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#endif // defined(_M_X64) || defined(__x86_64__) |
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static inline bool HaveSSE42() { |
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#if defined(_MSC_VER) |
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int cpu_info[4]; |
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__cpuid(cpu_info, 1); |
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return (cpu_info[2] & (1 << 20)) != 0; |
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#elif defined(__GNUC__) |
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unsigned int eax, ebx, ecx, edx; |
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__get_cpuid(1, &eax, &ebx, &ecx, &edx); |
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return (ecx & (1 << 20)) != 0; |
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#else |
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return false; |
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#endif |
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} |
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#endif // defined(LEVELDB_PLATFORM_POSIX_SSE) |
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// For further improvements see Intel publication at: |
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// http://download.intel.com/design/intarch/papers/323405.pdf |
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uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size) { |
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#if !defined(LEVELDB_PLATFORM_POSIX_SSE) |
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return 0; |
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#else |
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static bool have = HaveSSE42(); |
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if (!have) { |
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return 0; |
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} |
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const uint8_t *p = reinterpret_cast<const uint8_t *>(buf); |
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const uint8_t *e = p + size; |
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uint32_t l = crc ^ 0xffffffffu; |
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#define STEP1 do { \ |
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l = _mm_crc32_u8(l, *p++); \ |
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} while (0) |
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#define STEP4 do { \ |
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l = _mm_crc32_u32(l, LE_LOAD32(p)); \ |
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p += 4; \ |
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} while (0) |
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#define STEP8 do { \ |
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l = _mm_crc32_u64(l, LE_LOAD64(p)); \ |
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p += 8; \ |
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} while (0) |
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if (size > 16) { |
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// Process unaligned bytes |
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for (unsigned int i = reinterpret_cast<uintptr_t>(p) % 8; i; --i) { |
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STEP1; |
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} |
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// _mm_crc32_u64 is only available on x64. |
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#if defined(_M_X64) || defined(__x86_64__) |
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// Process 8 bytes at a time |
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while ((e-p) >= 8) { |
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STEP8; |
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} |
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// Process 4 bytes at a time |
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if ((e-p) >= 4) { |
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STEP4; |
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} |
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#else // !(defined(_M_X64) || defined(__x86_64__)) |
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// Process 4 bytes at a time |
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while ((e-p) >= 4) { |
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STEP4; |
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} |
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#endif // defined(_M_X64) || defined(__x86_64__) |
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} |
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// Process the last few bytes |
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while (p != e) { |
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STEP1; |
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} |
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#undef STEP8 |
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#undef STEP4 |
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#undef STEP1 |
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return l ^ 0xffffffffu; |
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#endif // defined(LEVELDB_PLATFORM_POSIX_SSE) |
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} |
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} // namespace port |
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} // namespace leveldb
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