ecccc63179
Summary: Implement a function to generate the crc32c of two combined strings. Suppose we have the string 1 (s1) with crc32c checksum crc32c_1 and string 2 (s2) with crc32c checksum crc32c_2, the new string is s1+s2 and its checksum is crc32c_new=Crc32cCombine(crc32c_1, crc32c_2, s2.size). Pull Request resolved: https://github.com/facebook/rocksdb/pull/8305 Test Plan: make check, added new testing case Reviewed By: pdillinger Differential Revision: D28651665 Pulled By: zhichao-cao fbshipit-source-id: c84116108388f11a81f6a217b49f99c70d4ffacf
58 lines
2.0 KiB
C++
58 lines
2.0 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include <stddef.h>
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#include <stdint.h>
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#include <string>
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#include "rocksdb/rocksdb_namespace.h"
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namespace ROCKSDB_NAMESPACE {
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namespace crc32c {
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extern std::string IsFastCrc32Supported();
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// Return the crc32c of concat(A, data[0,n-1]) where init_crc is the
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// crc32c of some string A. Extend() is often used to maintain the
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// crc32c of a stream of data.
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extern uint32_t Extend(uint32_t init_crc, const char* data, size_t n);
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// Takes two unmasked crc32c values, and the length of the string from
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// which `crc2` was computed, and computes a crc32c value for the
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// concatenation of the original two input strings. Running time is
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// ~ log(crc2len).
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extern uint32_t Crc32cCombine(uint32_t crc1, uint32_t crc2, size_t crc2len);
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// Return the crc32c of data[0,n-1]
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inline uint32_t Value(const char* data, size_t n) {
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return Extend(0, data, n);
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}
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static const uint32_t kMaskDelta = 0xa282ead8ul;
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// Return a masked representation of crc.
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//
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// Motivation: it is problematic to compute the CRC of a string that
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// contains embedded CRCs. Therefore we recommend that CRCs stored
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// somewhere (e.g., in files) should be masked before being stored.
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inline uint32_t Mask(uint32_t crc) {
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// Rotate right by 15 bits and add a constant.
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return ((crc >> 15) | (crc << 17)) + kMaskDelta;
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}
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// Return the crc whose masked representation is masked_crc.
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inline uint32_t Unmask(uint32_t masked_crc) {
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uint32_t rot = masked_crc - kMaskDelta;
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return ((rot >> 17) | (rot << 15));
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}
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} // namespace crc32c
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} // namespace ROCKSDB_NAMESPACE
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