// 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.

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_