mirror of
https://github.com/facebook/rocksdb.git
synced 2024-12-01 16:15:59 +00:00
46 lines
1.4 KiB
C
46 lines
1.4 KiB
C
|
// 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.
|
||
|
|
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));
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif // STORAGE_LEVELDB_UTIL_CRC32C_H_
|