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:
CRC(Init)47   JamCRC(uint32_t Init = 0xFFFFFFFFU) : CRC(Init) {}
48 
49   // Update the CRC calculation with Data.
50   void update(ArrayRef<uint8_t> Data);
51 
getCRC()52   uint32_t getCRC() const { return CRC; }
53 
54 private:
55   uint32_t CRC;
56 };
57 
58 } // end namespace llvm
59 
60 #endif
61