Inside Bitcoin

1// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file. See the AUTHORS file for names of contributors.
4
5#ifndef STORAGE_LEVELDB_UTIL_CRC32C_H_
6#define STORAGE_LEVELDB_UTIL_CRC32C_H_
7
8#include <stddef.h>
9#include <stdint.h>
10
11namespace leveldb {
12namespace crc32c {
13
14// Return the crc32c of concat(A, data[0,n-1]) where init_crc is the
15// crc32c of some string A.  Extend() is often used to maintain the
16// crc32c of a stream of data.
17uint32_t Extend(uint32_t init_crc, const char* data, size_t n);
18
19// Return the crc32c of data[0,n-1]
20inline uint32_t Value(const char* data, size_t n) { return Extend(0, data, n); }
21
22static const uint32_t kMaskDelta = 0xa282ead8ul;
23
24// Return a masked representation of crc.
25//
26// Motivation: it is problematic to compute the CRC of a string that
27// contains embedded CRCs.  Therefore we recommend that CRCs stored
28// somewhere (e.g., in files) should be masked before being stored.
29inline uint32_t Mask(uint32_t crc) {
30  // Rotate right by 15 bits and add a constant.
31  return ((crc >> 15) | (crc << 17)) + kMaskDelta;
32}
33
34// Return the crc whose masked representation is masked_crc.
35inline uint32_t Unmask(uint32_t masked_crc) {
36  uint32_t rot = masked_crc - kMaskDelta;
37  return ((rot >> 17) | (rot << 15));
38}
39
40}  // namespace crc32c
41}  // namespace leveldb
42
43#endif  // STORAGE_LEVELDB_UTIL_CRC32C_H_
44