| // Copyright (c) 2011-present, Facebook, Inc. All rights reserved. |
| // This source code is licensed under both the GPLv2 (found in the |
| // COPYING file in the root directory) and Apache 2.0 License |
| // (found in the LICENSE.Apache file in the root directory). |
| // |
| // 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. |
| |
| #pragma once |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| namespace rocksdb { |
| namespace crc32c { |
| |
| extern bool IsFastCrc32Supported(); |
| |
| // 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. |
| extern 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 rocksdb |