1 | /**********************************************************************
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2 | *
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3 | * CRC32.cpp
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4 | * Copyright (C) 2003 UNESCO
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5 | *
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6 | * A component of the Greenstone digital library software
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7 | * from the New Zealand Digital Library Project at the
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8 | * University of Waikato, New Zealand.
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9 | *
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10 | * This program is free software; you can redistribute it and/or modify
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11 | * it under the terms of the GNU General Public License as published by
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12 | * the Free Software Foundation; either version 2 of the License, or
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13 | * (at your option) any later version.
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14 | *
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15 | * This program is distributed in the hope that it will be useful,
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16 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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17 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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18 | * GNU General Public License for more details.
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19 | *
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20 | * You should have received a copy of the GNU General Public License
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21 | * along with this program; if not, write to the Free Software
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22 | * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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23 | *
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24 | *********************************************************************/
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25 |
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26 | ////////////////////////////////////////////////////////////////////////////////////
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27 | // CRC32.cpp --
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28 | //
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29 | // The CRC32 functions (Cyclic Redundancy Check) are used to
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30 | // calculate a sophisticated checksum based on the algebra of
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31 | // polynomials. The Cyclic Redundancy Check, is a way to detect
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32 | // bit errors that occur during data storage or transmission.
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33 | // The CRC-32 algorithm operates on a block of data as a single
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34 | // large numerical value. The algorithm divides this large value
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35 | // by the CRC-32 polynomial or generator polynomial, leaving the
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36 | // remainder 32-bit, which is the checksum.
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37 | //
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38 | // #include "stdafx.h"
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39 | #include <iomanip>
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40 | #include "CRC32.h"
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41 | #include "CRCTab.h"
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42 |
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43 | unsigned long CalcCRC32(const char *buf, unsigned len)
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44 | // Calculate a 32-bit CRC for a raw pattern of bytes.
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45 | // Returns a 32-bit checksum.
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46 | {
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47 | unsigned long CRC=0xffffffffL;
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48 | unsigned int n = len;
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49 |
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50 | while(n--)
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51 | CRC=crc32tab[(CRC ^ (*buf++)) & 0xFF] ^ ((CRC>>8) & 0x00ffffffL);
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52 |
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53 | return CRC ^ 0xffffffffL;
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54 | }
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55 |
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56 | unsigned long CalcCRC32(char *buf, unsigned len)
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57 | // Calculate a 32-bit CRC for a raw pattern of bytes.
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58 | // Returns a 32-bit checksum.
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59 | {
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60 | unsigned long CRC=0xffffffffL;
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61 | unsigned int n = len;
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62 | char *p = (char *)buf;
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63 | while(n--)
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64 | CRC=crc32tab[(CRC ^ (*p++)) & 0xFF] ^ ((CRC>>8) & 0x00ffffffL);
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65 |
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66 | return CRC ^ 0xffffffffL;
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67 | }
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68 |
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69 | unsigned long CalcCRC32(unsigned char c, unsigned long CRC)
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70 | // Calculate a 32-bit CRC table value for a single byte.
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71 | // NOTE: The initial CRC value must be set to 0xffffffffL
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72 | // and the final 32-bit value that must be XOR'ed with
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73 | // 0xffffffffL to obtain the checksum.
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74 | {
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75 | unsigned int i;
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76 | i = (unsigned int)c;
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77 | i &= 0xFF; // Reset all the bits
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78 | CRC=crc32tab[(CRC ^ i) & 0xFF] ^ ((CRC>>8) & 0x00ffffffL);
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79 | return CRC;
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80 | }
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81 |
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82 | unsigned long CalcCRC32(std::fstream &infile)
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83 | // Calculate a 32-bit CRC for a file. Assumes the stream
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84 | // is already open. Returns a 32-bit checksum.
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85 | {
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86 | unsigned long CRC=0xffffffffL;
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87 | #ifdef _WIN32
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88 | char c;
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89 | #else
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90 | unsigned char c;
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91 | #endif
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92 | unsigned int i;
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93 |
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94 | // Rewind to the start of the stream
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95 | infile.clear();
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96 | infile.seekg(0, std::ios::beg);
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97 | infile.seekp(0, std::ios::beg);
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98 |
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99 | while(!infile.eof()) {
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100 | c=infile.get();
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101 | i = (unsigned int)c;
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102 | i &= 0xFF; // Reset all the bits
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103 | if(infile.eof()) break;
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104 | CRC=crc32tab[(CRC ^ i) & 0xFF] ^ ((CRC>>8) & 0x00ffffffL);
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105 | }
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106 | return CRC ^ 0xffffffffL;
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107 | }
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108 |
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109 | #ifdef __USE_CRC32_TABLE_FUNCTIONS__
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110 | int MakeCRC32(ostream &stream)
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111 | // Write a CRC 32 table for a byte-wise 32-bit CRC calculation
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112 | // based on the Autodin/Ethernet/ADCCP polynomial of 0x4C11DB7:
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113 | // 0000 0100 1100 0001 0001 1101 1011 0111 (binary) or a poly of
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114 | // x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7 +x^5+x^4+x^2+x^1+x^0
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115 | // In this representation the coefficient of x^0 is stored in the
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116 | // MSB of the 32-bit word and the coefficient of x^31 is stored in
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117 | // the LSB. Thus 0x4C11DB7 becomes 0xEDB88320:
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118 | // 1110 1101 1011 1000 1000 0011 0010 0000 (binary)
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119 |
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120 | // Adding the polynomials is performed using an exclusive-or, and
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121 | // multiplying a polynomial by x is a right shift by one. If the
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122 | // polynomial is called "p", and each byte is represented as polynomial
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123 | // "q", with the lowest power in the most significant bit (so the byte
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124 | // 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32)
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125 | // mod "p", where "a" mod "b" means the remainder after dividing "a" by
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126 | // "b". This calculation is done using the shift-register method of
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127 | // multiplying and taking the remainder. The register is initialized
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128 | // to zero, and for each incoming bit, x^32 is added mod "p" to the
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129 | // register if the bit is a one (where x^32 mod p is p+x^32 = x^26+...+1),
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130 | // and the register is multiplied mod "p" by "x" (which is shifting right
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131 | // by one and adding x^32 mod "p" if the bit shifted out is a one.) This
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132 | // algorithm starts with the highest power (least significant bit) of "q"
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133 | // and repeats for all eight bits of "q".
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134 | {
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135 | unsigned long c; // CRC shift register
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136 | unsigned long e; // Polynomial exclusive-or pattern
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137 | int i; // Counter for all possible eight bit values
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138 | int k; // Byte being shifted into crc apparatus
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139 |
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140 | // Terms of polynomial defining this crc (except x^32):
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141 | static const int p[14] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
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142 |
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143 | // Make exclusive-or pattern from polynomial
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144 | e = 0;
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145 | for (i = 0; i < sizeof(p)/sizeof(int); i++)
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146 | e |= 1L << (31 - p[i]);
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147 |
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148 | // Compute and print table of CRC's, five per line
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149 | stream << endl;
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150 | stream << " 0x00000000U";
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151 | for (i = 1; i < 256; i++)
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152 | {
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153 | c = 0;
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154 | for (k = i | 256; k != 1; k >>= 1)
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155 | {
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156 | c = c & 1 ? (c >> 1) ^ e : c >> 1;
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157 | if (k & 1)
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158 | c ^= e;
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159 | }
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160 |
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161 | if(i % 5)
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162 | stream << ", 0x" << setfill('0') << setw(8) << hex << c << "U";
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163 | else
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164 | stream << "," << endl << " 0x" << setfill('0') << setw(8) << hex
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165 | << c << "U";
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166 | }
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167 | stream << endl;
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168 | return 1;
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169 | }
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170 | #endif // __USE_CRC32_TABLE_FUNCTIONS__
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