Differential D580 Diff 1484 src/leveldb/util/crc32c.cc

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src/leveldb/util/crc32c.cc

// Copyright (c) 2011 The LevelDB Authors. All rights reserved.		// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be		// 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.		// found in the LICENSE file. See the AUTHORS file for names of contributors.
//		//
// A portable implementation of crc32c, optimized to handle		// A portable implementation of crc32c, optimized to handle
// four bytes at a time.		// four bytes at a time.

#include "util/crc32c.h"		#include "util/crc32c.h"

#include <stdint.h>		#include <stdint.h>

		#include "port/port.h"
#include "util/coding.h"		#include "util/coding.h"

namespace leveldb {		namespace leveldb {
namespace crc32c {		namespace crc32c {

static const uint32_t table0_[256] = {		static const uint32_t table0_[256] = {
0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4,		0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4,
0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,		0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
▲ Show 20 Lines • Show All 259 Lines • ▼ Show 20 Lines	static const uint32_t table3_[256] = {
0x4a21617b, 0x9764cbc3, 0xf54642fa, 0x2803e842		0x4a21617b, 0x9764cbc3, 0xf54642fa, 0x2803e842
};		};

// Used to fetch a naturally-aligned 32-bit word in little endian byte-order		// Used to fetch a naturally-aligned 32-bit word in little endian byte-order
static inline uint32_t LE_LOAD32(const uint8_t *p) {		static inline uint32_t LE_LOAD32(const uint8_t *p) {
return DecodeFixed32(reinterpret_cast<const char*>(p));		return DecodeFixed32(reinterpret_cast<const char*>(p));
}		}

		// Determine if the CPU running this program can accelerate the CRC32C
		// calculation.
		static bool CanAccelerateCRC32C() {
		// port::AcceleretedCRC32C returns zero when unable to accelerate.
		static const char kTestCRCBuffer[] = "TestCRCBuffer";
		static const char kBufSize = sizeof(kTestCRCBuffer) - 1;
		static const uint32_t kTestCRCValue = 0xdcbc59fa;

		return port::AcceleratedCRC32C(0, kTestCRCBuffer, kBufSize) == kTestCRCValue;
		}

uint32_t Extend(uint32_t crc, const char* buf, size_t size) {		uint32_t Extend(uint32_t crc, const char* buf, size_t size) {
		static bool accelerate = CanAccelerateCRC32C();
		if (accelerate) {
		return port::AcceleratedCRC32C(crc, buf, size);
		}

const uint8_t p = reinterpret_cast<const uint8_t >(buf);		const uint8_t p = reinterpret_cast<const uint8_t >(buf);
const uint8_t *e = p + size;		const uint8_t *e = p + size;
uint32_t l = crc ^ 0xffffffffu;		uint32_t l = crc ^ 0xffffffffu;

#define STEP1 do { \		#define STEP1 do { \
int c = (l & 0xff) ^ *p++; \		int c = (l & 0xff) ^ *p++; \
l = table0_[c] ^ (l >> 8); \		l = table0_[c] ^ (l >> 8); \
} while (0)		} while (0)
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