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70269b4845
David added the JamCRC implementation in r246590. More recently, Eugene added a CRC-32 implementation in r357901, which falls back to zlib's crc32 function if present. These checksums are essentially the same, so having multiple implementations seems unnecessary. This replaces the CRC-32 implementation with the simpler one from JamCRC, and implements the JamCRC interface in terms of CRC-32 since this means it can use zlib's implementation when available, saving a few bytes and potentially making it faster. JamCRC took an ArrayRef<char> argument, and CRC-32 took a StringRef. This patch changes it to ArrayRef<uint8_t> which I think is the best choice, and simplifies a few of the callers nicely. Differential revision: https://reviews.llvm.org/D68570 llvm-svn: 374148
61 lines
1.6 KiB
C++
61 lines
1.6 KiB
C++
//===-- llvm/Support/CRC.h - Cyclic Redundancy Check-------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains implementations of CRC functions.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_CRC_H
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#define LLVM_SUPPORT_CRC_H
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#include "llvm/Support/DataTypes.h"
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namespace llvm {
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template <typename T> class ArrayRef;
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// Compute the CRC-32 of Data.
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uint32_t crc32(ArrayRef<uint8_t> Data);
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// Compute the running CRC-32 of Data, with CRC being the previous value of the
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// checksum.
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uint32_t crc32(uint32_t CRC, ArrayRef<uint8_t> Data);
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// Class for computing the JamCRC.
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//
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// We will use the "Rocksoft^tm Model CRC Algorithm" to describe the properties
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// of this CRC:
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// Width : 32
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// Poly : 04C11DB7
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// Init : FFFFFFFF
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// RefIn : True
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// RefOut : True
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// XorOut : 00000000
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// Check : 340BC6D9 (result of CRC for "123456789")
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//
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// In other words, this is the same as CRC-32, except that XorOut is 0 instead
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// of FFFFFFFF.
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//
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// N.B. We permit flexibility of the "Init" value. Some consumers of this need
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// it to be zero.
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class JamCRC {
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public:
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JamCRC(uint32_t Init = 0xFFFFFFFFU) : CRC(Init) {}
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// Update the CRC calculation with Data.
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void update(ArrayRef<uint8_t> Data);
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uint32_t getCRC() const { return CRC; }
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private:
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uint32_t CRC;
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};
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} // end namespace llvm
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#endif
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