1/* Copyright 2015 The TensorFlow Authors. All Rights Reserved.
2
3Licensed under the Apache License, Version 2.0 (the "License");
4you may not use this file except in compliance with the License.
5You may obtain a copy of the License at
6
7    http://www.apache.org/licenses/LICENSE-2.0
8
9Unless required by applicable law or agreed to in writing, software
10distributed under the License is distributed on an "AS IS" BASIS,
11WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12See the License for the specific language governing permissions and
13limitations under the License.
14==============================================================================*/
15
16#ifndef TENSORFLOW_LIB_HASH_CRC32C_H_
17#define TENSORFLOW_LIB_HASH_CRC32C_H_
18
19#include <stddef.h>
20#include "tensorflow/core/platform/types.h"
21
22namespace tensorflow {
23namespace crc32c {
24
25// Return the crc32c of concat(A, data[0,n-1]) where init_crc is the
26// crc32c of some string A.  Extend() is often used to maintain the
27// crc32c of a stream of data.
28extern uint32 Extend(uint32 init_crc, const char* data, size_t n);
29
30// Return the crc32c of data[0,n-1]
31inline uint32 Value(const char* data, size_t n) { return Extend(0, data, n); }
32
33static const uint32 kMaskDelta = 0xa282ead8ul;
34
35// Return a masked representation of crc.
36//
37// Motivation: it is problematic to compute the CRC of a string that
38// contains embedded CRCs.  Therefore we recommend that CRCs stored
39// somewhere (e.g., in files) should be masked before being stored.
40inline uint32 Mask(uint32 crc) {
41  // Rotate right by 15 bits and add a constant.
42  return ((crc >> 15) | (crc << 17)) + kMaskDelta;
43}
44
45// Return the crc whose masked representation is masked_crc.
46inline uint32 Unmask(uint32 masked_crc) {
47  uint32 rot = masked_crc - kMaskDelta;
48  return ((rot >> 17) | (rot << 15));
49}
50
51}  // namespace crc32c
52}  // namespace tensorflow
53
54#endif  // TENSORFLOW_LIB_HASH_CRC32C_H_
55