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// Copyright 2016 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
//
// A portable implementation of crc32c, optimized to handle
// four bytes at a time.
//
// In a separate source file to allow this accelerated CRC32C function to be
// compiled with the appropriate compiler flags to enable x86 SSE 4.2
// instructions.
#include <stdint.h>
#include <string.h>
#include "port/port.h"
#if defined(LEVELDB_PLATFORM_POSIX_SSE)
#if defined(_MSC_VER)
#include <intrin.h>
#elif defined(__GNUC__) && defined(__SSE4_2__)
#include <nmmintrin.h>
#include <cpuid.h>
#endif
#endif // defined(LEVELDB_PLATFORM_POSIX_SSE)
namespace leveldb {
namespace port {
#if defined(LEVELDB_PLATFORM_POSIX_SSE)
// Used to fetch a naturally-aligned 32-bit word in little endian byte-order
static inline uint32_t LE_LOAD32(const uint8_t *p) {
// SSE is x86 only, so ensured that |p| is always little-endian.
uint32_t word;
memcpy(&word, p, sizeof(word));
return word;
}
#if defined(_M_X64) || defined(__x86_64__) // LE_LOAD64 is only used on x64.
// Used to fetch a naturally-aligned 64-bit word in little endian byte-order
static inline uint64_t LE_LOAD64(const uint8_t *p) {
uint64_t dword;
memcpy(&dword, p, sizeof(dword));
return dword;
}
#endif // defined(_M_X64) || defined(__x86_64__)
static inline bool HaveSSE42() {
#if defined(_MSC_VER)
int cpu_info[4];
__cpuid(cpu_info, 1);
return (cpu_info[2] & (1 << 20)) != 0;
#elif defined(__GNUC__)
unsigned int eax, ebx, ecx, edx;
__get_cpuid(1, &eax, &ebx, &ecx, &edx);
return (ecx & (1 << 20)) != 0;
#else
return false;
#endif
}
#endif // defined(LEVELDB_PLATFORM_POSIX_SSE)
// For further improvements see Intel publication at:
// http://download.intel.com/design/intarch/papers/323405.pdf
uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size) {
#if !defined(LEVELDB_PLATFORM_POSIX_SSE)
return 0;
#else
static bool have = HaveSSE42();
if (!have) {
return 0;
}
const uint8_t *p = reinterpret_cast<const uint8_t *>(buf);
const uint8_t *e = p + size;
uint32_t l = crc ^ 0xffffffffu;
#define STEP1 do { \
l = _mm_crc32_u8(l, *p++); \
} while (0)
#define STEP4 do { \
l = _mm_crc32_u32(l, LE_LOAD32(p)); \
p += 4; \
} while (0)
#define STEP8 do { \
l = _mm_crc32_u64(l, LE_LOAD64(p)); \
p += 8; \
} while (0)
if (size > 16) {
// Point x at first 8-byte aligned byte in string. This must be inside the
// string, due to the size check above.
const uintptr_t pval = reinterpret_cast<uintptr_t>(p);
const uint8_t* x = reinterpret_cast<const uint8_t*>(((pval + 7) >> 3) << 3);
// Process bytes until p is 8-byte aligned.
while (p != x) {
STEP1;
}
// _mm_crc32_u64 is only available on x64.
#if defined(_M_X64) || defined(__x86_64__)
// Process 8 bytes at a time
while ((e-p) >= 8) {
STEP8;
}
// Process 4 bytes at a time
if ((e-p) >= 4) {
STEP4;
}
#else // !(defined(_M_X64) || defined(__x86_64__))
// Process 4 bytes at a time
while ((e-p) >= 4) {
STEP4;
}
#endif // defined(_M_X64) || defined(__x86_64__)
}
// Process the last few bytes
while (p != e) {
STEP1;
}
#undef STEP8
#undef STEP4
#undef STEP1
return l ^ 0xffffffffu;
#endif // defined(LEVELDB_PLATFORM_POSIX_SSE)
}
} // namespace port
} // namespace leveldb
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