1 | /* crc32.c -- compute the CRC-32 of a data stream |
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2 | * Copyright (C) 1995-2003 Mark Adler |
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3 | * For conditions of distribution and use, see copyright notice in zlib.h |
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4 | * |
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5 | * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster |
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6 | * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing |
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7 | * tables for updating the shift register in one step with three exclusive-ors |
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8 | * instead of four steps with four exclusive-ors. This results about a factor |
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9 | * of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. |
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10 | */ |
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11 | |
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12 | /* @(#) $Id: crc32.cc,v 1.1 2005/05/12 21:04:53 duns Exp $ */ |
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13 | |
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14 | /* |
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15 | Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore |
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16 | protection on the static variables used to control the first-use generation |
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17 | of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should |
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18 | first call get_crc_table() to initialize the tables before allowing more than |
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19 | one thread to use crc32(). |
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20 | */ |
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21 | |
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22 | #ifdef MAKECRCH |
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23 | # include <stdio.h> |
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24 | # ifndef DYNAMIC_CRC_TABLE |
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25 | # define DYNAMIC_CRC_TABLE |
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26 | # endif /* !DYNAMIC_CRC_TABLE */ |
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27 | #endif /* MAKECRCH */ |
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28 | |
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29 | #include "zutil.h" /* for STDC and FAR definitions */ |
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30 | |
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31 | #define local static |
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32 | |
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33 | /* Find a four-byte integer type for crc32_little() and crc32_big(). */ |
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34 | #ifndef NOBYFOUR |
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35 | # ifdef STDC /* need ANSI C limits.h to determine sizes */ |
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36 | # include <limits.h> |
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37 | # define BYFOUR |
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38 | # if (UINT_MAX == 0xffffffffUL) |
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39 | typedef unsigned int u4; |
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40 | # else |
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41 | # if (ULONG_MAX == 0xffffffffUL) |
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42 | typedef unsigned long u4; |
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43 | # else |
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44 | # if (USHRT_MAX == 0xffffffffUL) |
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45 | typedef unsigned short u4; |
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46 | # else |
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47 | # undef BYFOUR /* can't find a four-byte integer type! */ |
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48 | # endif |
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49 | # endif |
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50 | # endif |
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51 | # endif /* STDC */ |
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52 | #endif /* !NOBYFOUR */ |
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53 | |
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54 | /* Definitions for doing the crc four data bytes at a time. */ |
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55 | #ifdef BYFOUR |
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56 | # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ |
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57 | (((w)&0xff00)<<8)+(((w)&0xff)<<24)) |
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58 | local unsigned long crc32_little OF((unsigned long, |
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59 | const unsigned char FAR *, unsigned)); |
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60 | local unsigned long crc32_big OF((unsigned long, |
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61 | const unsigned char FAR *, unsigned)); |
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62 | # define TBLS 8 |
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63 | #else |
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64 | # define TBLS 1 |
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65 | #endif /* BYFOUR */ |
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66 | |
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67 | #ifdef DYNAMIC_CRC_TABLE |
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68 | |
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69 | local volatile int crc_table_empty = 1; |
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70 | local unsigned long FAR crc_table[TBLS][256]; |
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71 | local void make_crc_table OF((void)); |
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72 | #ifdef MAKECRCH |
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73 | local void write_table OF((FILE *, const unsigned long FAR *)); |
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74 | #endif /* MAKECRCH */ |
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75 | |
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76 | /* |
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77 | Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: |
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78 | 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. |
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79 | |
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80 | Polynomials over GF(2) are represented in binary, one bit per coefficient, |
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81 | with the lowest powers in the most significant bit. Then adding polynomials |
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82 | is just exclusive-or, and multiplying a polynomial by x is a right shift by |
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83 | one. If we call the above polynomial p, and represent a byte as the |
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84 | polynomial q, also with the lowest power in the most significant bit (so the |
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85 | byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, |
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86 | where a mod b means the remainder after dividing a by b. |
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87 | |
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88 | This calculation is done using the shift-register method of multiplying and |
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89 | taking the remainder. The register is initialized to zero, and for each |
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90 | incoming bit, x^32 is added mod p to the register if the bit is a one (where |
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91 | x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by |
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92 | x (which is shifting right by one and adding x^32 mod p if the bit shifted |
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93 | out is a one). We start with the highest power (least significant bit) of |
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94 | q and repeat for all eight bits of q. |
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95 | |
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96 | The first table is simply the CRC of all possible eight bit values. This is |
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97 | all the information needed to generate CRCs on data a byte at a time for all |
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98 | combinations of CRC register values and incoming bytes. The remaining tables |
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99 | allow for word-at-a-time CRC calculation for both big-endian and little- |
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100 | endian machines, where a word is four bytes. |
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101 | */ |
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102 | local void make_crc_table() |
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103 | { |
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104 | unsigned long c; |
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105 | int n, k; |
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106 | unsigned long poly; /* polynomial exclusive-or pattern */ |
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107 | /* terms of polynomial defining this crc (except x^32): */ |
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108 | static volatile int first = 1; /* flag to limit concurrent making */ |
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109 | static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; |
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110 | |
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111 | /* See if another task is already doing this (not thread-safe, but better |
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112 | than nothing -- significantly reduces duration of vulnerability in |
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113 | case the advice about DYNAMIC_CRC_TABLE is ignored) */ |
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114 | if (first) { |
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115 | first = 0; |
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116 | |
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117 | /* make exclusive-or pattern from polynomial (0xedb88320UL) */ |
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118 | poly = 0UL; |
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119 | for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) |
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120 | poly |= 1UL << (31 - p[n]); |
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121 | |
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122 | /* generate a crc for every 8-bit value */ |
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123 | for (n = 0; n < 256; n++) { |
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124 | c = (unsigned long)n; |
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125 | for (k = 0; k < 8; k++) |
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126 | c = c & 1 ? poly ^ (c >> 1) : c >> 1; |
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127 | crc_table[0][n] = c; |
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128 | } |
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129 | |
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130 | #ifdef BYFOUR |
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131 | /* generate crc for each value followed by one, two, and three zeros, |
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132 | and then the byte reversal of those as well as the first table */ |
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133 | for (n = 0; n < 256; n++) { |
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134 | c = crc_table[0][n]; |
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135 | crc_table[4][n] = REV(c); |
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136 | for (k = 1; k < 4; k++) { |
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137 | c = crc_table[0][c & 0xff] ^ (c >> 8); |
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138 | crc_table[k][n] = c; |
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139 | crc_table[k + 4][n] = REV(c); |
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140 | } |
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141 | } |
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142 | #endif /* BYFOUR */ |
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143 | |
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144 | crc_table_empty = 0; |
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145 | } |
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146 | else { /* not first */ |
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147 | /* wait for the other guy to finish (not efficient, but rare) */ |
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148 | while (crc_table_empty) |
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149 | ; |
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150 | } |
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151 | |
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152 | #ifdef MAKECRCH |
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153 | /* write out CRC tables to crc32.h */ |
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154 | { |
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155 | FILE *out; |
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156 | |
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157 | out = fopen("crc32.h", "w"); |
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158 | if (out == NULL) return; |
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159 | fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); |
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160 | fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); |
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161 | fprintf(out, "local const unsigned long FAR "); |
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162 | fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); |
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163 | write_table(out, crc_table[0]); |
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164 | # ifdef BYFOUR |
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165 | fprintf(out, "#ifdef BYFOUR\n"); |
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166 | for (k = 1; k < 8; k++) { |
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167 | fprintf(out, " },\n {\n"); |
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168 | write_table(out, crc_table[k]); |
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169 | } |
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170 | fprintf(out, "#endif\n"); |
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171 | # endif /* BYFOUR */ |
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172 | fprintf(out, " }\n};\n"); |
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173 | fclose(out); |
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174 | } |
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175 | #endif /* MAKECRCH */ |
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176 | } |
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177 | |
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178 | #ifdef MAKECRCH |
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179 | local void write_table(FILE *out, const unsigned long FAR *table) |
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180 | { |
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181 | int n; |
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182 | |
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183 | for (n = 0; n < 256; n++) |
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184 | fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n], |
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185 | n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); |
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186 | } |
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187 | #endif /* MAKECRCH */ |
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188 | |
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189 | #else /* !DYNAMIC_CRC_TABLE */ |
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190 | /* ======================================================================== |
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191 | * Tables of CRC-32s of all single-byte values, made by make_crc_table(). |
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192 | */ |
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193 | #include "crc32.h" |
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194 | #endif /* DYNAMIC_CRC_TABLE */ |
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195 | |
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196 | /* ========================================================================= |
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197 | * This function can be used by asm versions of crc32() |
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198 | */ |
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199 | const unsigned long FAR * ZEXPORT get_crc_table() |
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200 | { |
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201 | #ifdef DYNAMIC_CRC_TABLE |
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202 | if (crc_table_empty) |
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203 | make_crc_table(); |
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204 | #endif /* DYNAMIC_CRC_TABLE */ |
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205 | return (const unsigned long FAR *)crc_table; |
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206 | } |
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207 | |
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208 | /* ========================================================================= */ |
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209 | #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) |
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210 | #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 |
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211 | |
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212 | /* ========================================================================= */ |
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213 | unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
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214 | { |
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215 | if (buf == Z_NULL) return 0UL; |
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216 | |
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217 | #ifdef DYNAMIC_CRC_TABLE |
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218 | if (crc_table_empty) |
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219 | make_crc_table(); |
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220 | #endif /* DYNAMIC_CRC_TABLE */ |
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221 | |
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222 | #ifdef BYFOUR |
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223 | if (sizeof(void *) == sizeof(ptrdiff_t)) { |
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224 | u4 endian; |
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225 | |
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226 | endian = 1; |
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227 | if (*((unsigned char *)(&endian))) |
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228 | return crc32_little(crc, buf, len); |
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229 | else |
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230 | return crc32_big(crc, buf, len); |
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231 | } |
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232 | #endif /* BYFOUR */ |
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233 | crc = crc ^ 0xffffffffUL; |
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234 | while (len >= 8) { |
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235 | DO8; |
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236 | len -= 8; |
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237 | } |
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238 | if (len) do { |
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239 | DO1; |
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240 | } while (--len); |
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241 | return crc ^ 0xffffffffUL; |
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242 | } |
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243 | |
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244 | #ifdef BYFOUR |
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245 | |
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246 | /* ========================================================================= */ |
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247 | #define DOLIT4 c ^= *buf4++; \ |
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248 | c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ |
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249 | crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] |
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250 | #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 |
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251 | |
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252 | /* ========================================================================= */ |
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253 | local unsigned long crc32_little(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
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254 | { |
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255 | register u4 c; |
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256 | register const u4 FAR *buf4; |
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257 | |
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258 | c = (u4)crc; |
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259 | c = ~c; |
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260 | while (len && ((ptrdiff_t)buf & 3)) { |
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261 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
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262 | len--; |
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263 | } |
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264 | |
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265 | buf4 = (const u4 FAR *)buf; |
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266 | while (len >= 32) { |
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267 | DOLIT32; |
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268 | len -= 32; |
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269 | } |
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270 | while (len >= 4) { |
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271 | DOLIT4; |
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272 | len -= 4; |
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273 | } |
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274 | buf = (const unsigned char FAR *)buf4; |
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275 | |
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276 | if (len) do { |
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277 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
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278 | } while (--len); |
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279 | c = ~c; |
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280 | return (unsigned long)c; |
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281 | } |
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282 | |
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283 | /* ========================================================================= */ |
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284 | #define DOBIG4 c ^= *++buf4; \ |
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285 | c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ |
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286 | crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] |
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287 | #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 |
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288 | |
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289 | /* ========================================================================= */ |
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290 | local unsigned long crc32_big(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
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291 | { |
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292 | register u4 c; |
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293 | register const u4 FAR *buf4; |
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294 | |
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295 | c = REV((u4)crc); |
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296 | c = ~c; |
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297 | while (len && ((ptrdiff_t)buf & 3)) { |
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298 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
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299 | len--; |
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300 | } |
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301 | |
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302 | buf4 = (const u4 FAR *)buf; |
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303 | buf4--; |
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304 | while (len >= 32) { |
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305 | DOBIG32; |
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306 | len -= 32; |
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307 | } |
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308 | while (len >= 4) { |
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309 | DOBIG4; |
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310 | len -= 4; |
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311 | } |
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312 | buf4++; |
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313 | buf = (const unsigned char FAR *)buf4; |
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314 | |
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315 | if (len) do { |
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316 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
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317 | } while (--len); |
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318 | c = ~c; |
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319 | return (unsigned long)(REV(c)); |
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320 | } |
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321 | |
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322 | #endif /* BYFOUR */ |
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