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      1 //===-- llvm/Support/CRC.h - Cyclic Redundancy Check-------------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 //
      9 // This file contains implementations of CRC functions.
     10 //
     11 //===----------------------------------------------------------------------===//
     12 
     13 #ifndef LLVM_SUPPORT_CRC_H
     14 #define LLVM_SUPPORT_CRC_H
     15 
     16 #include "llvm/Support/DataTypes.h"
     17 
     18 namespace llvm {
     19 template <typename T> class ArrayRef;
     20 
     21 // Compute the CRC-32 of Data.
     22 uint32_t crc32(ArrayRef<uint8_t> Data);
     23 
     24 // Compute the running CRC-32 of Data, with CRC being the previous value of the
     25 // checksum.
     26 uint32_t crc32(uint32_t CRC, ArrayRef<uint8_t> Data);
     27 
     28 // Class for computing the JamCRC.
     29 //
     30 // We will use the "Rocksoft^tm Model CRC Algorithm" to describe the properties
     31 // of this CRC:
     32 //   Width  : 32
     33 //   Poly   : 04C11DB7
     34 //   Init   : FFFFFFFF
     35 //   RefIn  : True
     36 //   RefOut : True
     37 //   XorOut : 00000000
     38 //   Check  : 340BC6D9 (result of CRC for "123456789")
     39 //
     40 // In other words, this is the same as CRC-32, except that XorOut is 0 instead
     41 // of FFFFFFFF.
     42 //
     43 // N.B.  We permit flexibility of the "Init" value.  Some consumers of this need
     44 //       it to be zero.
     45 class JamCRC {
     46 public:
     47   JamCRC(uint32_t Init = 0xFFFFFFFFU) : CRC(Init) {}
     48 
     49   // Update the CRC calculation with Data.
     50   void update(ArrayRef<uint8_t> Data);
     51 
     52   uint32_t getCRC() const { return CRC; }
     53 
     54 private:
     55   uint32_t CRC;
     56 };
     57 
     58 } // end namespace llvm
     59 
     60 #endif
     61