ceph/src/rocksdb/util/crc32c.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under the BSD-style license found in the
   3 //  LICENSE file in the root directory of this source tree. An additional grant
   4 //  of patent rights can be found in the PATENTS file in the same directory.
   5 //
   6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   7 // Use of this source code is governed by a BSD-style license that can be
   8 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   9
  10 #pragma once
  11 #include <stddef.h>
  12 #include <stdint.h>
  13
  14 namespace rocksdb {
  15 namespace crc32c {
  16
  17 extern bool IsFastCrc32Supported();
  18
  19 // Return the crc32c of concat(A, data[0,n-1]) where init_crc is the
  20 // crc32c of some string A.  Extend() is often used to maintain the
  21 // crc32c of a stream of data.
  22 extern uint32_t Extend(uint32_t init_crc, const char* data, size_t n);
  23
  24 // Return the crc32c of data[0,n-1]
  25 inline uint32_t Value(const char* data, size_t n) {
  26   return Extend(0, data, n);
  27 }
  28
  29 static const uint32_t kMaskDelta = 0xa282ead8ul;
  30
  31 // Return a masked representation of crc.
  32 //
  33 // Motivation: it is problematic to compute the CRC of a string that
  34 // contains embedded CRCs.  Therefore we recommend that CRCs stored
  35 // somewhere (e.g., in files) should be masked before being stored.
  36 inline uint32_t Mask(uint32_t crc) {
  37   // Rotate right by 15 bits and add a constant.
  38   return ((crc >> 15) | (crc << 17)) + kMaskDelta;
  39 }
  40
  41 // Return the crc whose masked representation is masked_crc.
  42 inline uint32_t Unmask(uint32_t masked_crc) {
  43   uint32_t rot = masked_crc - kMaskDelta;
  44   return ((rot >> 17) | (rot << 15));
  45 }
  46
  47 }  // namespace crc32c
  48 }  // namespace rocksdb