tomFlowee
c63519fa47
The leveldb and univalue 3rd party libraries are not installed and not needed by anyone outside of the Hub. So move them there, making it easier for 3rd party usage.
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));
|
|
}
|
|
|
|
} // namespace crc32c
|
|
} // namespace leveldb
|
|
|
|
#endif // STORAGE_LEVELDB_UTIL_CRC32C_H_
|