You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
43 lines
1.4 KiB
43 lines
1.4 KiB
// 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 <cstddef>
|
|
#include <cstdint>
|
|
|
|
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_
|