git / moonbite-core / src/leveldb/util/crc32c.h · raw

// Copyright (c) 2011 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.#ifndef STORAGE_LEVELDB_UTIL_CRC32C_H_#define STORAGE_LEVELDB_UTIL_CRC32C_H_#include <stddef.h>#include <stdint.h>namespace leveldb {namespace crc32c {// Return the crc32c of concat(A, data[0,n-1]) where init_crc is the// crc32c of some string A.  Extend() is often used to maintain the// crc32c of a stream of data.uint32_t Extend(uint32_t init_crc, const char* data, size_t n);// Return the crc32c of data[0,n-1]inline uint32_t Value(const char* data, size_t n) { return Extend(0, data, n); }static const uint32_t kMaskDelta = 0xa282ead8ul;// Return a masked representation of crc.//// Motivation: it is problematic to compute the CRC of a string that// contains embedded CRCs.  Therefore we recommend that CRCs stored// somewhere (e.g., in files) should be masked before being stored.inline uint32_t Mask(uint32_t crc) {  // Rotate right by 15 bits and add a constant.  return ((crc >> 15) | (crc << 17)) + kMaskDelta;}// Return the crc whose masked representation is masked_crc.inline uint32_t Unmask(uint32_t masked_crc) {  uint32_t rot = masked_crc - kMaskDelta;  return ((rot >> 17) | (rot << 15));}}  // namespace crc32c}  // namespace leveldb#endif  // STORAGE_LEVELDB_UTIL_CRC32C_H_