Mercurial > repos > blastem
annotate zlib/crc32.c @ 1998:0740d90812ee
Enter debugger when a VDP data port read would cause a CPU lockup
author | Mike Pavone <pavone@retrodev.com> |
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date | Sun, 28 Jun 2020 22:53:52 -0700 |
parents | 00d788dac91a |
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1 /* crc32.c -- compute the CRC-32 of a data stream |
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2 * Copyright (C) 1995-2006, 2010, 2011, 2012, 2016 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 in about a |
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9 * factor 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 /* @(#) $Id$ */ |
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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 DYNAMIC_CRC_TABLE and MAKECRCH can be #defined to write out crc32.h. |
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22 */ |
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23 |
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24 #ifdef MAKECRCH |
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25 # include <stdio.h> |
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26 # ifndef DYNAMIC_CRC_TABLE |
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27 # define DYNAMIC_CRC_TABLE |
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28 # endif /* !DYNAMIC_CRC_TABLE */ |
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29 #endif /* MAKECRCH */ |
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30 |
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31 #include "zutil.h" /* for STDC and FAR definitions */ |
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32 |
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33 /* Definitions for doing the crc four data bytes at a time. */ |
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34 #if !defined(NOBYFOUR) && defined(Z_U4) |
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35 # define BYFOUR |
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36 #endif |
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37 #ifdef BYFOUR |
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38 local unsigned long crc32_little OF((unsigned long, |
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39 const unsigned char FAR *, z_size_t)); |
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40 local unsigned long crc32_big OF((unsigned long, |
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41 const unsigned char FAR *, z_size_t)); |
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42 # define TBLS 8 |
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43 #else |
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44 # define TBLS 1 |
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45 #endif /* BYFOUR */ |
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46 |
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47 /* Local functions for crc concatenation */ |
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48 local unsigned long gf2_matrix_times OF((unsigned long *mat, |
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49 unsigned long vec)); |
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50 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat)); |
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51 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2)); |
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52 |
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53 |
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54 #ifdef DYNAMIC_CRC_TABLE |
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55 |
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56 local volatile int crc_table_empty = 1; |
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57 local z_crc_t FAR crc_table[TBLS][256]; |
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58 local void make_crc_table OF((void)); |
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59 #ifdef MAKECRCH |
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60 local void write_table OF((FILE *, const z_crc_t FAR *)); |
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61 #endif /* MAKECRCH */ |
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62 /* |
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63 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: |
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64 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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65 |
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66 Polynomials over GF(2) are represented in binary, one bit per coefficient, |
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67 with the lowest powers in the most significant bit. Then adding polynomials |
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68 is just exclusive-or, and multiplying a polynomial by x is a right shift by |
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69 one. If we call the above polynomial p, and represent a byte as the |
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70 polynomial q, also with the lowest power in the most significant bit (so the |
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71 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, |
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72 where a mod b means the remainder after dividing a by b. |
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73 |
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74 This calculation is done using the shift-register method of multiplying and |
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75 taking the remainder. The register is initialized to zero, and for each |
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76 incoming bit, x^32 is added mod p to the register if the bit is a one (where |
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77 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by |
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78 x (which is shifting right by one and adding x^32 mod p if the bit shifted |
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79 out is a one). We start with the highest power (least significant bit) of |
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80 q and repeat for all eight bits of q. |
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81 |
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82 The first table is simply the CRC of all possible eight bit values. This is |
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83 all the information needed to generate CRCs on data a byte at a time for all |
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84 combinations of CRC register values and incoming bytes. The remaining tables |
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85 allow for word-at-a-time CRC calculation for both big-endian and little- |
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86 endian machines, where a word is four bytes. |
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87 */ |
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88 local void make_crc_table() |
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89 { |
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90 z_crc_t c; |
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91 int n, k; |
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92 z_crc_t poly; /* polynomial exclusive-or pattern */ |
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93 /* terms of polynomial defining this crc (except x^32): */ |
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94 static volatile int first = 1; /* flag to limit concurrent making */ |
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95 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; |
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96 |
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97 /* See if another task is already doing this (not thread-safe, but better |
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98 than nothing -- significantly reduces duration of vulnerability in |
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99 case the advice about DYNAMIC_CRC_TABLE is ignored) */ |
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100 if (first) { |
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101 first = 0; |
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102 |
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103 /* make exclusive-or pattern from polynomial (0xedb88320UL) */ |
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104 poly = 0; |
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105 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++) |
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106 poly |= (z_crc_t)1 << (31 - p[n]); |
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107 |
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108 /* generate a crc for every 8-bit value */ |
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109 for (n = 0; n < 256; n++) { |
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110 c = (z_crc_t)n; |
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111 for (k = 0; k < 8; k++) |
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112 c = c & 1 ? poly ^ (c >> 1) : c >> 1; |
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113 crc_table[0][n] = c; |
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114 } |
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115 |
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116 #ifdef BYFOUR |
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117 /* generate crc for each value followed by one, two, and three zeros, |
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118 and then the byte reversal of those as well as the first table */ |
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119 for (n = 0; n < 256; n++) { |
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120 c = crc_table[0][n]; |
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121 crc_table[4][n] = ZSWAP32(c); |
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122 for (k = 1; k < 4; k++) { |
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123 c = crc_table[0][c & 0xff] ^ (c >> 8); |
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124 crc_table[k][n] = c; |
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125 crc_table[k + 4][n] = ZSWAP32(c); |
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126 } |
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127 } |
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128 #endif /* BYFOUR */ |
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129 |
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130 crc_table_empty = 0; |
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131 } |
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132 else { /* not first */ |
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133 /* wait for the other guy to finish (not efficient, but rare) */ |
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134 while (crc_table_empty) |
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135 ; |
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136 } |
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137 |
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138 #ifdef MAKECRCH |
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139 /* write out CRC tables to crc32.h */ |
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140 { |
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141 FILE *out; |
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142 |
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143 out = fopen("crc32.h", "w"); |
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144 if (out == NULL) return; |
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145 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); |
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146 fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); |
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147 fprintf(out, "local const z_crc_t FAR "); |
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148 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); |
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149 write_table(out, crc_table[0]); |
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150 # ifdef BYFOUR |
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151 fprintf(out, "#ifdef BYFOUR\n"); |
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152 for (k = 1; k < 8; k++) { |
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153 fprintf(out, " },\n {\n"); |
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154 write_table(out, crc_table[k]); |
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155 } |
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156 fprintf(out, "#endif\n"); |
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157 # endif /* BYFOUR */ |
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158 fprintf(out, " }\n};\n"); |
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159 fclose(out); |
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160 } |
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161 #endif /* MAKECRCH */ |
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162 } |
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163 |
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164 #ifdef MAKECRCH |
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165 local void write_table(out, table) |
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166 FILE *out; |
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167 const z_crc_t FAR *table; |
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168 { |
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169 int n; |
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170 |
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171 for (n = 0; n < 256; n++) |
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172 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", |
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173 (unsigned long)(table[n]), |
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174 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); |
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175 } |
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176 #endif /* MAKECRCH */ |
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177 |
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178 #else /* !DYNAMIC_CRC_TABLE */ |
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179 /* ======================================================================== |
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180 * Tables of CRC-32s of all single-byte values, made by make_crc_table(). |
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181 */ |
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182 #include "crc32.h" |
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183 #endif /* DYNAMIC_CRC_TABLE */ |
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184 |
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185 /* ========================================================================= |
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186 * This function can be used by asm versions of crc32() |
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187 */ |
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188 const z_crc_t FAR * ZEXPORT get_crc_table() |
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189 { |
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190 #ifdef DYNAMIC_CRC_TABLE |
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191 if (crc_table_empty) |
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192 make_crc_table(); |
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193 #endif /* DYNAMIC_CRC_TABLE */ |
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194 return (const z_crc_t FAR *)crc_table; |
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195 } |
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196 |
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197 /* ========================================================================= */ |
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198 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) |
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199 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 |
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200 |
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201 /* ========================================================================= */ |
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202 unsigned long ZEXPORT crc32_z(crc, buf, len) |
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203 unsigned long crc; |
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204 const unsigned char FAR *buf; |
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205 z_size_t len; |
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206 { |
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207 if (buf == Z_NULL) return 0UL; |
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208 |
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209 #ifdef DYNAMIC_CRC_TABLE |
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210 if (crc_table_empty) |
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211 make_crc_table(); |
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212 #endif /* DYNAMIC_CRC_TABLE */ |
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213 |
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214 #ifdef BYFOUR |
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215 if (sizeof(void *) == sizeof(ptrdiff_t)) { |
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216 z_crc_t endian; |
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217 |
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218 endian = 1; |
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219 if (*((unsigned char *)(&endian))) |
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220 return crc32_little(crc, buf, len); |
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221 else |
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222 return crc32_big(crc, buf, len); |
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223 } |
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224 #endif /* BYFOUR */ |
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225 crc = crc ^ 0xffffffffUL; |
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226 while (len >= 8) { |
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227 DO8; |
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228 len -= 8; |
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229 } |
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230 if (len) do { |
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231 DO1; |
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232 } while (--len); |
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233 return crc ^ 0xffffffffUL; |
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234 } |
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235 |
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236 /* ========================================================================= */ |
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237 unsigned long ZEXPORT crc32(crc, buf, len) |
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238 unsigned long crc; |
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239 const unsigned char FAR *buf; |
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240 uInt len; |
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241 { |
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242 return crc32_z(crc, buf, len); |
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243 } |
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244 |
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245 #ifdef BYFOUR |
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246 |
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247 /* |
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248 This BYFOUR code accesses the passed unsigned char * buffer with a 32-bit |
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249 integer pointer type. This violates the strict aliasing rule, where a |
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250 compiler can assume, for optimization purposes, that two pointers to |
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251 fundamentally different types won't ever point to the same memory. This can |
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252 manifest as a problem only if one of the pointers is written to. This code |
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253 only reads from those pointers. So long as this code remains isolated in |
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254 this compilation unit, there won't be a problem. For this reason, this code |
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255 should not be copied and pasted into a compilation unit in which other code |
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256 writes to the buffer that is passed to these routines. |
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257 */ |
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258 |
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259 /* ========================================================================= */ |
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260 #define DOLIT4 c ^= *buf4++; \ |
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261 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ |
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262 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] |
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263 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 |
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264 |
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265 /* ========================================================================= */ |
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266 local unsigned long crc32_little(crc, buf, len) |
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267 unsigned long crc; |
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268 const unsigned char FAR *buf; |
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269 z_size_t len; |
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270 { |
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271 register z_crc_t c; |
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272 register const z_crc_t FAR *buf4; |
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273 |
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274 c = (z_crc_t)crc; |
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275 c = ~c; |
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276 while (len && ((ptrdiff_t)buf & 3)) { |
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277 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
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278 len--; |
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279 } |
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280 |
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281 buf4 = (const z_crc_t FAR *)(const void FAR *)buf; |
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282 while (len >= 32) { |
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283 DOLIT32; |
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284 len -= 32; |
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285 } |
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286 while (len >= 4) { |
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287 DOLIT4; |
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288 len -= 4; |
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289 } |
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290 buf = (const unsigned char FAR *)buf4; |
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291 |
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292 if (len) do { |
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293 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
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294 } while (--len); |
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295 c = ~c; |
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296 return (unsigned long)c; |
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297 } |
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298 |
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299 /* ========================================================================= */ |
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300 #define DOBIG4 c ^= *buf4++; \ |
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301 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ |
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302 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] |
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303 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 |
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304 |
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305 /* ========================================================================= */ |
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306 local unsigned long crc32_big(crc, buf, len) |
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307 unsigned long crc; |
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308 const unsigned char FAR *buf; |
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309 z_size_t len; |
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310 { |
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311 register z_crc_t c; |
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312 register const z_crc_t FAR *buf4; |
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313 |
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314 c = ZSWAP32((z_crc_t)crc); |
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315 c = ~c; |
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316 while (len && ((ptrdiff_t)buf & 3)) { |
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317 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
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318 len--; |
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319 } |
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320 |
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321 buf4 = (const z_crc_t FAR *)(const void FAR *)buf; |
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322 while (len >= 32) { |
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323 DOBIG32; |
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324 len -= 32; |
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325 } |
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326 while (len >= 4) { |
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327 DOBIG4; |
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328 len -= 4; |
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329 } |
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330 buf = (const unsigned char FAR *)buf4; |
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331 |
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332 if (len) do { |
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333 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
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334 } while (--len); |
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335 c = ~c; |
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336 return (unsigned long)(ZSWAP32(c)); |
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337 } |
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338 |
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339 #endif /* BYFOUR */ |
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340 |
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341 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */ |
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342 |
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343 /* ========================================================================= */ |
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344 local unsigned long gf2_matrix_times(mat, vec) |
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345 unsigned long *mat; |
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346 unsigned long vec; |
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347 { |
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348 unsigned long sum; |
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349 |
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350 sum = 0; |
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351 while (vec) { |
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352 if (vec & 1) |
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353 sum ^= *mat; |
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354 vec >>= 1; |
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355 mat++; |
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356 } |
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357 return sum; |
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358 } |
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359 |
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360 /* ========================================================================= */ |
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361 local void gf2_matrix_square(square, mat) |
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362 unsigned long *square; |
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363 unsigned long *mat; |
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364 { |
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365 int n; |
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366 |
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367 for (n = 0; n < GF2_DIM; n++) |
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368 square[n] = gf2_matrix_times(mat, mat[n]); |
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369 } |
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370 |
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371 /* ========================================================================= */ |
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372 local uLong crc32_combine_(crc1, crc2, len2) |
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373 uLong crc1; |
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374 uLong crc2; |
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375 z_off64_t len2; |
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376 { |
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377 int n; |
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378 unsigned long row; |
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379 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */ |
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380 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */ |
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381 |
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382 /* degenerate case (also disallow negative lengths) */ |
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383 if (len2 <= 0) |
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384 return crc1; |
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385 |
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386 /* put operator for one zero bit in odd */ |
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387 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */ |
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388 row = 1; |
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389 for (n = 1; n < GF2_DIM; n++) { |
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390 odd[n] = row; |
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391 row <<= 1; |
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392 } |
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393 |
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394 /* put operator for two zero bits in even */ |
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395 gf2_matrix_square(even, odd); |
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396 |
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397 /* put operator for four zero bits in odd */ |
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398 gf2_matrix_square(odd, even); |
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399 |
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400 /* apply len2 zeros to crc1 (first square will put the operator for one |
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401 zero byte, eight zero bits, in even) */ |
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402 do { |
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403 /* apply zeros operator for this bit of len2 */ |
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404 gf2_matrix_square(even, odd); |
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405 if (len2 & 1) |
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406 crc1 = gf2_matrix_times(even, crc1); |
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407 len2 >>= 1; |
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408 |
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409 /* if no more bits set, then done */ |
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410 if (len2 == 0) |
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411 break; |
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412 |
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413 /* another iteration of the loop with odd and even swapped */ |
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414 gf2_matrix_square(odd, even); |
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415 if (len2 & 1) |
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416 crc1 = gf2_matrix_times(odd, crc1); |
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417 len2 >>= 1; |
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418 |
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419 /* if no more bits set, then done */ |
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420 } while (len2 != 0); |
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421 |
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422 /* return combined crc */ |
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423 crc1 ^= crc2; |
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424 return crc1; |
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425 } |
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426 |
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427 /* ========================================================================= */ |
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428 uLong ZEXPORT crc32_combine(crc1, crc2, len2) |
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429 uLong crc1; |
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430 uLong crc2; |
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431 z_off_t len2; |
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432 { |
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433 return crc32_combine_(crc1, crc2, len2); |
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434 } |
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435 |
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436 uLong ZEXPORT crc32_combine64(crc1, crc2, len2) |
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437 uLong crc1; |
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438 uLong crc2; |
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439 z_off64_t len2; |
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440 { |
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441 return crc32_combine_(crc1, crc2, len2); |
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442 } |