1 | /* crc32.c -- compute the CRC-32 of a data stream
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2 | * Copyright (C) 1995-2022 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 | * This interleaved implementation of a CRC makes use of pipelined multiple
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6 | * arithmetic-logic units, commonly found in modern CPU cores. It is due to
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7 | * Kadatch and Jenkins (2010). See doc/crc-doc.1.0.pdf in this distribution.
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8 | */
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9 |
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10 | /* @(#) $Id$ */
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11 |
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12 | /*
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13 | Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
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14 | protection on the static variables used to control the first-use generation
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15 | of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
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16 | first call get_crc_table() to initialize the tables before allowing more than
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17 | one thread to use crc32().
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18 |
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19 | MAKECRCH can be #defined to write out crc32.h. A main() routine is also
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20 | produced, so that this one source file can be compiled to an executable.
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21 | */
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22 |
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23 | #ifdef MAKECRCH
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24 | # include <stdio.h>
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25 | # ifndef DYNAMIC_CRC_TABLE
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26 | # define DYNAMIC_CRC_TABLE
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27 | # endif /* !DYNAMIC_CRC_TABLE */
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28 | #endif /* MAKECRCH */
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29 |
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30 | #include "zutil.h" /* for Z_U4, Z_U8, z_crc_t, and FAR definitions */
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31 |
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32 | /*
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33 | A CRC of a message is computed on N braids of words in the message, where
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34 | each word consists of W bytes (4 or 8). If N is 3, for example, then three
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35 | running sparse CRCs are calculated respectively on each braid, at these
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36 | indices in the array of words: 0, 3, 6, ..., 1, 4, 7, ..., and 2, 5, 8, ...
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37 | This is done starting at a word boundary, and continues until as many blocks
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38 | of N * W bytes as are available have been processed. The results are combined
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39 | into a single CRC at the end. For this code, N must be in the range 1..6 and
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40 | W must be 4 or 8. The upper limit on N can be increased if desired by adding
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41 | more #if blocks, extending the patterns apparent in the code. In addition,
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42 | crc32.h would need to be regenerated, if the maximum N value is increased.
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43 |
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44 | N and W are chosen empirically by benchmarking the execution time on a given
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45 | processor. The choices for N and W below were based on testing on Intel Kaby
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46 | Lake i7, AMD Ryzen 7, ARM Cortex-A57, Sparc64-VII, PowerPC POWER9, and MIPS64
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47 | Octeon II processors. The Intel, AMD, and ARM processors were all fastest
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48 | with N=5, W=8. The Sparc, PowerPC, and MIPS64 were all fastest at N=5, W=4.
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49 | They were all tested with either gcc or clang, all using the -O3 optimization
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50 | level. Your mileage may vary.
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51 | */
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52 |
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53 | /* Define N */
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54 | #ifdef Z_TESTN
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55 | # define N Z_TESTN
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56 | #else
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57 | # define N 5
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58 | #endif
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59 | #if N < 1 || N > 6
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60 | # error N must be in 1..6
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61 | #endif
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62 |
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63 | /*
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64 | z_crc_t must be at least 32 bits. z_word_t must be at least as long as
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65 | z_crc_t. It is assumed here that z_word_t is either 32 bits or 64 bits, and
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66 | that bytes are eight bits.
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67 | */
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68 |
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69 | /*
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70 | Define W and the associated z_word_t type. If W is not defined, then a
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71 | braided calculation is not used, and the associated tables and code are not
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72 | compiled.
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73 | */
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74 | #ifdef Z_TESTW
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75 | # if Z_TESTW-1 != -1
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76 | # define W Z_TESTW
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77 | # endif
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78 | #else
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79 | # ifdef MAKECRCH
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80 | # define W 8 /* required for MAKECRCH */
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81 | # else
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82 | # if defined(__x86_64__) || defined(__aarch64__)
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83 | # define W 8
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84 | # else
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85 | # define W 4
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86 | # endif
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87 | # endif
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88 | #endif
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89 | #ifdef W
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90 | # if W == 8 && defined(Z_U8)
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91 | typedef Z_U8 z_word_t;
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92 | # elif defined(Z_U4)
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93 | # undef W
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94 | # define W 4
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95 | typedef Z_U4 z_word_t;
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96 | # else
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97 | # undef W
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98 | # endif
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99 | #endif
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100 |
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101 | /* If available, use the ARM processor CRC32 instruction. */
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102 | #if defined(__aarch64__) && defined(__ARM_FEATURE_CRC32) && W == 8
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103 | # define ARMCRC32
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104 | #endif
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105 |
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106 | /* Local functions. */
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107 | local z_crc_t multmodp OF((z_crc_t a, z_crc_t b));
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108 | local z_crc_t x2nmodp OF((z_off64_t n, unsigned k));
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109 |
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110 | #if defined(W) && (!defined(ARMCRC32) || defined(DYNAMIC_CRC_TABLE))
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111 | local z_word_t byte_swap OF((z_word_t word));
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112 | #endif
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113 |
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114 | #if defined(W) && !defined(ARMCRC32)
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115 | local z_crc_t crc_word OF((z_word_t data));
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116 | local z_word_t crc_word_big OF((z_word_t data));
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117 | #endif
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118 |
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119 | #if defined(W) && (!defined(ARMCRC32) || defined(DYNAMIC_CRC_TABLE))
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120 | /*
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121 | Swap the bytes in a z_word_t to convert between little and big endian. Any
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122 | self-respecting compiler will optimize this to a single machine byte-swap
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123 | instruction, if one is available. This assumes that word_t is either 32 bits
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124 | or 64 bits.
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125 | */
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126 | local z_word_t byte_swap(word)
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127 | z_word_t word;
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128 | {
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129 | # if W == 8
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130 | return
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131 | (word & 0xff00000000000000) >> 56 |
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132 | (word & 0xff000000000000) >> 40 |
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133 | (word & 0xff0000000000) >> 24 |
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134 | (word & 0xff00000000) >> 8 |
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135 | (word & 0xff000000) << 8 |
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136 | (word & 0xff0000) << 24 |
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137 | (word & 0xff00) << 40 |
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138 | (word & 0xff) << 56;
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139 | # else /* W == 4 */
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140 | return
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141 | (word & 0xff000000) >> 24 |
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142 | (word & 0xff0000) >> 8 |
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143 | (word & 0xff00) << 8 |
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144 | (word & 0xff) << 24;
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145 | # endif
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146 | }
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147 | #endif
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148 |
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149 | /* CRC polynomial. */
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150 | #define POLY 0xedb88320 /* p(x) reflected, with x^32 implied */
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151 |
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152 | #ifdef DYNAMIC_CRC_TABLE
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153 |
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154 | local z_crc_t FAR crc_table[256];
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155 | local z_crc_t FAR x2n_table[32];
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156 | local void make_crc_table OF((void));
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157 | #ifdef W
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158 | local z_word_t FAR crc_big_table[256];
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159 | local z_crc_t FAR crc_braid_table[W][256];
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160 | local z_word_t FAR crc_braid_big_table[W][256];
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161 | local void braid OF((z_crc_t [][256], z_word_t [][256], int, int));
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162 | #endif
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163 | #ifdef MAKECRCH
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164 | local void write_table OF((FILE *, const z_crc_t FAR *, int));
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165 | local void write_table32hi OF((FILE *, const z_word_t FAR *, int));
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166 | local void write_table64 OF((FILE *, const z_word_t FAR *, int));
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167 | #endif /* MAKECRCH */
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168 |
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169 | /*
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170 | Define a once() function depending on the availability of atomics. If this is
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171 | compiled with DYNAMIC_CRC_TABLE defined, and if CRCs will be computed in
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172 | multiple threads, and if atomics are not available, then get_crc_table() must
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173 | be called to initialize the tables and must return before any threads are
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174 | allowed to compute or combine CRCs.
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175 | */
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176 |
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177 | /* Definition of once functionality. */
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178 | typedef struct once_s once_t;
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179 | local void once OF((once_t *, void (*)(void)));
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180 |
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181 | /* Check for the availability of atomics. */
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182 | #if defined(__STDC__) && __STDC_VERSION__ >= 201112L && \
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183 | !defined(__STDC_NO_ATOMICS__)
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184 |
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185 | #include <stdatomic.h>
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186 |
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187 | /* Structure for once(), which must be initialized with ONCE_INIT. */
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188 | struct once_s {
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189 | atomic_flag begun;
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190 | atomic_int done;
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191 | };
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192 | #define ONCE_INIT {ATOMIC_FLAG_INIT, 0}
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193 |
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194 | /*
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195 | Run the provided init() function exactly once, even if multiple threads
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196 | invoke once() at the same time. The state must be a once_t initialized with
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197 | ONCE_INIT.
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198 | */
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199 | local void once(state, init)
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200 | once_t *state;
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201 | void (*init)(void);
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202 | {
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203 | if (!atomic_load(&state->done)) {
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204 | if (atomic_flag_test_and_set(&state->begun))
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205 | while (!atomic_load(&state->done))
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206 | ;
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207 | else {
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208 | init();
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209 | atomic_store(&state->done, 1);
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210 | }
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211 | }
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212 | }
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213 |
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214 | #else /* no atomics */
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215 |
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216 | /* Structure for once(), which must be initialized with ONCE_INIT. */
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217 | struct once_s {
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218 | volatile int begun;
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219 | volatile int done;
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220 | };
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221 | #define ONCE_INIT {0, 0}
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222 |
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223 | /* Test and set. Alas, not atomic, but tries to minimize the period of
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224 | vulnerability. */
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225 | local int test_and_set OF((int volatile *));
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226 | local int test_and_set(flag)
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227 | int volatile *flag;
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228 | {
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229 | int was;
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230 |
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231 | was = *flag;
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232 | *flag = 1;
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233 | return was;
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234 | }
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235 |
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236 | /* Run the provided init() function once. This is not thread-safe. */
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237 | local void once(state, init)
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238 | once_t *state;
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239 | void (*init)(void);
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240 | {
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241 | if (!state->done) {
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242 | if (test_and_set(&state->begun))
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243 | while (!state->done)
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244 | ;
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245 | else {
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246 | init();
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247 | state->done = 1;
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248 | }
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249 | }
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250 | }
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251 |
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252 | #endif
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253 |
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254 | /* State for once(). */
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255 | local once_t made = ONCE_INIT;
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256 |
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257 | /*
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258 | Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
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259 | 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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260 |
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261 | Polynomials over GF(2) are represented in binary, one bit per coefficient,
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262 | with the lowest powers in the most significant bit. Then adding polynomials
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263 | is just exclusive-or, and multiplying a polynomial by x is a right shift by
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264 | one. If we call the above polynomial p, and represent a byte as the
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265 | polynomial q, also with the lowest power in the most significant bit (so the
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266 | byte 0xb1 is the polynomial x^7+x^3+x^2+1), then the CRC is (q*x^32) mod p,
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267 | where a mod b means the remainder after dividing a by b.
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268 |
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269 | This calculation is done using the shift-register method of multiplying and
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270 | taking the remainder. The register is initialized to zero, and for each
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271 | incoming bit, x^32 is added mod p to the register if the bit is a one (where
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272 | x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by x
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273 | (which is shifting right by one and adding x^32 mod p if the bit shifted out
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274 | is a one). We start with the highest power (least significant bit) of q and
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275 | repeat for all eight bits of q.
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276 |
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277 | The table is simply the CRC of all possible eight bit values. This is all the
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278 | information needed to generate CRCs on data a byte at a time for all
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279 | combinations of CRC register values and incoming bytes.
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280 | */
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281 |
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282 | local void make_crc_table()
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283 | {
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284 | unsigned i, j, n;
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285 | z_crc_t p;
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286 |
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287 | /* initialize the CRC of bytes tables */
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288 | for (i = 0; i < 256; i++) {
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289 | p = i;
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290 | for (j = 0; j < 8; j++)
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291 | p = p & 1 ? (p >> 1) ^ POLY : p >> 1;
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292 | crc_table[i] = p;
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293 | #ifdef W
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294 | crc_big_table[i] = byte_swap(p);
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295 | #endif
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296 | }
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297 |
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298 | /* initialize the x^2^n mod p(x) table */
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299 | p = (z_crc_t)1 << 30; /* x^1 */
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300 | x2n_table[0] = p;
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301 | for (n = 1; n < 32; n++)
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302 | x2n_table[n] = p = multmodp(p, p);
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303 |
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304 | #ifdef W
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305 | /* initialize the braiding tables -- needs x2n_table[] */
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306 | braid(crc_braid_table, crc_braid_big_table, N, W);
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307 | #endif
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308 |
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309 | #ifdef MAKECRCH
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310 | {
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311 | /*
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312 | The crc32.h header file contains tables for both 32-bit and 64-bit
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313 | z_word_t's, and so requires a 64-bit type be available. In that case,
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314 | z_word_t must be defined to be 64-bits. This code then also generates
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315 | and writes out the tables for the case that z_word_t is 32 bits.
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316 | */
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317 | #if !defined(W) || W != 8
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318 | # error Need a 64-bit integer type in order to generate crc32.h.
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319 | #endif
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320 | FILE *out;
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321 | int k, n;
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322 | z_crc_t ltl[8][256];
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323 | z_word_t big[8][256];
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324 |
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325 | out = fopen("crc32.h", "w");
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326 | if (out == NULL) return;
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327 |
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328 | /* write out little-endian CRC table to crc32.h */
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329 | fprintf(out,
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330 | "/* crc32.h -- tables for rapid CRC calculation\n"
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331 | " * Generated automatically by crc32.c\n */\n"
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332 | "\n"
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333 | "local const z_crc_t FAR crc_table[] = {\n"
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334 | " ");
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335 | write_table(out, crc_table, 256);
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336 | fprintf(out,
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337 | "};\n");
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338 |
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339 | /* write out big-endian CRC table for 64-bit z_word_t to crc32.h */
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340 | fprintf(out,
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341 | "\n"
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342 | "#ifdef W\n"
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343 | "\n"
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344 | "#if W == 8\n"
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345 | "\n"
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346 | "local const z_word_t FAR crc_big_table[] = {\n"
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347 | " ");
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348 | write_table64(out, crc_big_table, 256);
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349 | fprintf(out,
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350 | "};\n");
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351 |
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352 | /* write out big-endian CRC table for 32-bit z_word_t to crc32.h */
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353 | fprintf(out,
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354 | "\n"
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355 | "#else /* W == 4 */\n"
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356 | "\n"
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357 | "local const z_word_t FAR crc_big_table[] = {\n"
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358 | " ");
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359 | write_table32hi(out, crc_big_table, 256);
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360 | fprintf(out,
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361 | "};\n"
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362 | "\n"
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363 | "#endif\n");
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364 |
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365 | /* write out braid tables for each value of N */
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366 | for (n = 1; n <= 6; n++) {
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367 | fprintf(out,
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368 | "\n"
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369 | "#if N == %d\n", n);
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370 |
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371 | /* compute braid tables for this N and 64-bit word_t */
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372 | braid(ltl, big, n, 8);
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373 |
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374 | /* write out braid tables for 64-bit z_word_t to crc32.h */
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375 | fprintf(out,
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376 | "\n"
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377 | "#if W == 8\n"
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378 | "\n"
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379 | "local const z_crc_t FAR crc_braid_table[][256] = {\n");
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380 | for (k = 0; k < 8; k++) {
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381 | fprintf(out, " {");
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382 | write_table(out, ltl[k], 256);
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383 | fprintf(out, "}%s", k < 7 ? ",\n" : "");
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384 | }
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385 | fprintf(out,
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386 | "};\n"
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387 | "\n"
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388 | "local const z_word_t FAR crc_braid_big_table[][256] = {\n");
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389 | for (k = 0; k < 8; k++) {
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390 | fprintf(out, " {");
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391 | write_table64(out, big[k], 256);
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392 | fprintf(out, "}%s", k < 7 ? ",\n" : "");
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393 | }
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394 | fprintf(out,
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395 | "};\n");
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396 |
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397 | /* compute braid tables for this N and 32-bit word_t */
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398 | braid(ltl, big, n, 4);
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399 |
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400 | /* write out braid tables for 32-bit z_word_t to crc32.h */
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401 | fprintf(out,
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402 | "\n"
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403 | "#else /* W == 4 */\n"
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404 | "\n"
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405 | "local const z_crc_t FAR crc_braid_table[][256] = {\n");
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406 | for (k = 0; k < 4; k++) {
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407 | fprintf(out, " {");
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408 | write_table(out, ltl[k], 256);
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409 | fprintf(out, "}%s", k < 3 ? ",\n" : "");
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410 | }
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411 | fprintf(out,
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412 | "};\n"
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413 | "\n"
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414 | "local const z_word_t FAR crc_braid_big_table[][256] = {\n");
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415 | for (k = 0; k < 4; k++) {
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416 | fprintf(out, " {");
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417 | write_table32hi(out, big[k], 256);
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418 | fprintf(out, "}%s", k < 3 ? ",\n" : "");
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419 | }
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420 | fprintf(out,
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421 | "};\n"
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422 | "\n"
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423 | "#endif\n"
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424 | "\n"
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425 | "#endif\n");
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426 | }
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427 | fprintf(out,
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428 | "\n"
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429 | "#endif\n");
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430 |
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431 | /* write out zeros operator table to crc32.h */
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432 | fprintf(out,
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433 | "\n"
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434 | "local const z_crc_t FAR x2n_table[] = {\n"
|
---|
435 | " ");
|
---|
436 | write_table(out, x2n_table, 32);
|
---|
437 | fprintf(out,
|
---|
438 | "};\n");
|
---|
439 | fclose(out);
|
---|
440 | }
|
---|
441 | #endif /* MAKECRCH */
|
---|
442 | }
|
---|
443 |
|
---|
444 | #ifdef MAKECRCH
|
---|
445 |
|
---|
446 | /*
|
---|
447 | Write the 32-bit values in table[0..k-1] to out, five per line in
|
---|
448 | hexadecimal separated by commas.
|
---|
449 | */
|
---|
450 | local void write_table(out, table, k)
|
---|
451 | FILE *out;
|
---|
452 | const z_crc_t FAR *table;
|
---|
453 | int k;
|
---|
454 | {
|
---|
455 | int n;
|
---|
456 |
|
---|
457 | for (n = 0; n < k; n++)
|
---|
458 | fprintf(out, "%s0x%08lx%s", n == 0 || n % 5 ? "" : " ",
|
---|
459 | (unsigned long)(table[n]),
|
---|
460 | n == k - 1 ? "" : (n % 5 == 4 ? ",\n" : ", "));
|
---|
461 | }
|
---|
462 |
|
---|
463 | /*
|
---|
464 | Write the high 32-bits of each value in table[0..k-1] to out, five per line
|
---|
465 | in hexadecimal separated by commas.
|
---|
466 | */
|
---|
467 | local void write_table32hi(out, table, k)
|
---|
468 | FILE *out;
|
---|
469 | const z_word_t FAR *table;
|
---|
470 | int k;
|
---|
471 | {
|
---|
472 | int n;
|
---|
473 |
|
---|
474 | for (n = 0; n < k; n++)
|
---|
475 | fprintf(out, "%s0x%08lx%s", n == 0 || n % 5 ? "" : " ",
|
---|
476 | (unsigned long)(table[n] >> 32),
|
---|
477 | n == k - 1 ? "" : (n % 5 == 4 ? ",\n" : ", "));
|
---|
478 | }
|
---|
479 |
|
---|
480 | /*
|
---|
481 | Write the 64-bit values in table[0..k-1] to out, three per line in
|
---|
482 | hexadecimal separated by commas. This assumes that if there is a 64-bit
|
---|
483 | type, then there is also a long long integer type, and it is at least 64
|
---|
484 | bits. If not, then the type cast and format string can be adjusted
|
---|
485 | accordingly.
|
---|
486 | */
|
---|
487 | local void write_table64(out, table, k)
|
---|
488 | FILE *out;
|
---|
489 | const z_word_t FAR *table;
|
---|
490 | int k;
|
---|
491 | {
|
---|
492 | int n;
|
---|
493 |
|
---|
494 | for (n = 0; n < k; n++)
|
---|
495 | fprintf(out, "%s0x%016llx%s", n == 0 || n % 3 ? "" : " ",
|
---|
496 | (unsigned long long)(table[n]),
|
---|
497 | n == k - 1 ? "" : (n % 3 == 2 ? ",\n" : ", "));
|
---|
498 | }
|
---|
499 |
|
---|
500 | /* Actually do the deed. */
|
---|
501 | int main()
|
---|
502 | {
|
---|
503 | make_crc_table();
|
---|
504 | return 0;
|
---|
505 | }
|
---|
506 |
|
---|
507 | #endif /* MAKECRCH */
|
---|
508 |
|
---|
509 | #ifdef W
|
---|
510 | /*
|
---|
511 | Generate the little and big-endian braid tables for the given n and z_word_t
|
---|
512 | size w. Each array must have room for w blocks of 256 elements.
|
---|
513 | */
|
---|
514 | local void braid(ltl, big, n, w)
|
---|
515 | z_crc_t ltl[][256];
|
---|
516 | z_word_t big[][256];
|
---|
517 | int n;
|
---|
518 | int w;
|
---|
519 | {
|
---|
520 | int k;
|
---|
521 | z_crc_t i, p, q;
|
---|
522 | for (k = 0; k < w; k++) {
|
---|
523 | p = x2nmodp((n * w + 3 - k) << 3, 0);
|
---|
524 | ltl[k][0] = 0;
|
---|
525 | big[w - 1 - k][0] = 0;
|
---|
526 | for (i = 1; i < 256; i++) {
|
---|
527 | ltl[k][i] = q = multmodp(i << 24, p);
|
---|
528 | big[w - 1 - k][i] = byte_swap(q);
|
---|
529 | }
|
---|
530 | }
|
---|
531 | }
|
---|
532 | #endif
|
---|
533 |
|
---|
534 | #else /* !DYNAMIC_CRC_TABLE */
|
---|
535 | /* ========================================================================
|
---|
536 | * Tables for byte-wise and braided CRC-32 calculations, and a table of powers
|
---|
537 | * of x for combining CRC-32s, all made by make_crc_table().
|
---|
538 | */
|
---|
539 | #include "crc32.h"
|
---|
540 | #endif /* DYNAMIC_CRC_TABLE */
|
---|
541 |
|
---|
542 | /* ========================================================================
|
---|
543 | * Routines used for CRC calculation. Some are also required for the table
|
---|
544 | * generation above.
|
---|
545 | */
|
---|
546 |
|
---|
547 | /*
|
---|
548 | Return a(x) multiplied by b(x) modulo p(x), where p(x) is the CRC polynomial,
|
---|
549 | reflected. For speed, this requires that a not be zero.
|
---|
550 | */
|
---|
551 | local z_crc_t multmodp(a, b)
|
---|
552 | z_crc_t a;
|
---|
553 | z_crc_t b;
|
---|
554 | {
|
---|
555 | z_crc_t m, p;
|
---|
556 |
|
---|
557 | m = (z_crc_t)1 << 31;
|
---|
558 | p = 0;
|
---|
559 | for (;;) {
|
---|
560 | if (a & m) {
|
---|
561 | p ^= b;
|
---|
562 | if ((a & (m - 1)) == 0)
|
---|
563 | break;
|
---|
564 | }
|
---|
565 | m >>= 1;
|
---|
566 | b = b & 1 ? (b >> 1) ^ POLY : b >> 1;
|
---|
567 | }
|
---|
568 | return p;
|
---|
569 | }
|
---|
570 |
|
---|
571 | /*
|
---|
572 | Return x^(n * 2^k) modulo p(x). Requires that x2n_table[] has been
|
---|
573 | initialized.
|
---|
574 | */
|
---|
575 | local z_crc_t x2nmodp(n, k)
|
---|
576 | z_off64_t n;
|
---|
577 | unsigned k;
|
---|
578 | {
|
---|
579 | z_crc_t p;
|
---|
580 |
|
---|
581 | p = (z_crc_t)1 << 31; /* x^0 == 1 */
|
---|
582 | while (n) {
|
---|
583 | if (n & 1)
|
---|
584 | p = multmodp(x2n_table[k & 31], p);
|
---|
585 | n >>= 1;
|
---|
586 | k++;
|
---|
587 | }
|
---|
588 | return p;
|
---|
589 | }
|
---|
590 |
|
---|
591 | /* =========================================================================
|
---|
592 | * This function can be used by asm versions of crc32(), and to force the
|
---|
593 | * generation of the CRC tables in a threaded application.
|
---|
594 | */
|
---|
595 | const z_crc_t FAR * ZEXPORT get_crc_table()
|
---|
596 | {
|
---|
597 | #ifdef DYNAMIC_CRC_TABLE
|
---|
598 | once(&made, make_crc_table);
|
---|
599 | #endif /* DYNAMIC_CRC_TABLE */
|
---|
600 | return (const z_crc_t FAR *)crc_table;
|
---|
601 | }
|
---|
602 |
|
---|
603 | /* =========================================================================
|
---|
604 | * Use ARM machine instructions if available. This will compute the CRC about
|
---|
605 | * ten times faster than the braided calculation. This code does not check for
|
---|
606 | * the presence of the CRC instruction at run time. __ARM_FEATURE_CRC32 will
|
---|
607 | * only be defined if the compilation specifies an ARM processor architecture
|
---|
608 | * that has the instructions. For example, compiling with -march=armv8.1-a or
|
---|
609 | * -march=armv8-a+crc, or -march=native if the compile machine has the crc32
|
---|
610 | * instructions.
|
---|
611 | */
|
---|
612 | #ifdef ARMCRC32
|
---|
613 |
|
---|
614 | /*
|
---|
615 | Constants empirically determined to maximize speed. These values are from
|
---|
616 | measurements on a Cortex-A57. Your mileage may vary.
|
---|
617 | */
|
---|
618 | #define Z_BATCH 3990 /* number of words in a batch */
|
---|
619 | #define Z_BATCH_ZEROS 0xa10d3d0c /* computed from Z_BATCH = 3990 */
|
---|
620 | #define Z_BATCH_MIN 800 /* fewest words in a final batch */
|
---|
621 |
|
---|
622 | unsigned long ZEXPORT crc32_z(crc, buf, len)
|
---|
623 | unsigned long crc;
|
---|
624 | const unsigned char FAR *buf;
|
---|
625 | z_size_t len;
|
---|
626 | {
|
---|
627 | z_crc_t val;
|
---|
628 | z_word_t crc1, crc2;
|
---|
629 | const z_word_t *word;
|
---|
630 | z_word_t val0, val1, val2;
|
---|
631 | z_size_t last, last2, i;
|
---|
632 | z_size_t num;
|
---|
633 |
|
---|
634 | /* Return initial CRC, if requested. */
|
---|
635 | if (buf == Z_NULL) return 0;
|
---|
636 |
|
---|
637 | #ifdef DYNAMIC_CRC_TABLE
|
---|
638 | once(&made, make_crc_table);
|
---|
639 | #endif /* DYNAMIC_CRC_TABLE */
|
---|
640 |
|
---|
641 | /* Pre-condition the CRC */
|
---|
642 | crc = (~crc) & 0xffffffff;
|
---|
643 |
|
---|
644 | /* Compute the CRC up to a word boundary. */
|
---|
645 | while (len && ((z_size_t)buf & 7) != 0) {
|
---|
646 | len--;
|
---|
647 | val = *buf++;
|
---|
648 | __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
|
---|
649 | }
|
---|
650 |
|
---|
651 | /* Prepare to compute the CRC on full 64-bit words word[0..num-1]. */
|
---|
652 | word = (z_word_t const *)buf;
|
---|
653 | num = len >> 3;
|
---|
654 | len &= 7;
|
---|
655 |
|
---|
656 | /* Do three interleaved CRCs to realize the throughput of one crc32x
|
---|
657 | instruction per cycle. Each CRC is calculated on Z_BATCH words. The
|
---|
658 | three CRCs are combined into a single CRC after each set of batches. */
|
---|
659 | while (num >= 3 * Z_BATCH) {
|
---|
660 | crc1 = 0;
|
---|
661 | crc2 = 0;
|
---|
662 | for (i = 0; i < Z_BATCH; i++) {
|
---|
663 | val0 = word[i];
|
---|
664 | val1 = word[i + Z_BATCH];
|
---|
665 | val2 = word[i + 2 * Z_BATCH];
|
---|
666 | __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
|
---|
667 | __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
|
---|
668 | __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
|
---|
669 | }
|
---|
670 | word += 3 * Z_BATCH;
|
---|
671 | num -= 3 * Z_BATCH;
|
---|
672 | crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc1;
|
---|
673 | crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc2;
|
---|
674 | }
|
---|
675 |
|
---|
676 | /* Do one last smaller batch with the remaining words, if there are enough
|
---|
677 | to pay for the combination of CRCs. */
|
---|
678 | last = num / 3;
|
---|
679 | if (last >= Z_BATCH_MIN) {
|
---|
680 | last2 = last << 1;
|
---|
681 | crc1 = 0;
|
---|
682 | crc2 = 0;
|
---|
683 | for (i = 0; i < last; i++) {
|
---|
684 | val0 = word[i];
|
---|
685 | val1 = word[i + last];
|
---|
686 | val2 = word[i + last2];
|
---|
687 | __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
|
---|
688 | __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
|
---|
689 | __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
|
---|
690 | }
|
---|
691 | word += 3 * last;
|
---|
692 | num -= 3 * last;
|
---|
693 | val = x2nmodp(last, 6);
|
---|
694 | crc = multmodp(val, crc) ^ crc1;
|
---|
695 | crc = multmodp(val, crc) ^ crc2;
|
---|
696 | }
|
---|
697 |
|
---|
698 | /* Compute the CRC on any remaining words. */
|
---|
699 | for (i = 0; i < num; i++) {
|
---|
700 | val0 = word[i];
|
---|
701 | __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
|
---|
702 | }
|
---|
703 | word += num;
|
---|
704 |
|
---|
705 | /* Complete the CRC on any remaining bytes. */
|
---|
706 | buf = (const unsigned char FAR *)word;
|
---|
707 | while (len) {
|
---|
708 | len--;
|
---|
709 | val = *buf++;
|
---|
710 | __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
|
---|
711 | }
|
---|
712 |
|
---|
713 | /* Return the CRC, post-conditioned. */
|
---|
714 | return crc ^ 0xffffffff;
|
---|
715 | }
|
---|
716 |
|
---|
717 | #else
|
---|
718 |
|
---|
719 | #ifdef W
|
---|
720 |
|
---|
721 | /*
|
---|
722 | Return the CRC of the W bytes in the word_t data, taking the
|
---|
723 | least-significant byte of the word as the first byte of data, without any pre
|
---|
724 | or post conditioning. This is used to combine the CRCs of each braid.
|
---|
725 | */
|
---|
726 | local z_crc_t crc_word(data)
|
---|
727 | z_word_t data;
|
---|
728 | {
|
---|
729 | int k;
|
---|
730 | for (k = 0; k < W; k++)
|
---|
731 | data = (data >> 8) ^ crc_table[data & 0xff];
|
---|
732 | return (z_crc_t)data;
|
---|
733 | }
|
---|
734 |
|
---|
735 | local z_word_t crc_word_big(data)
|
---|
736 | z_word_t data;
|
---|
737 | {
|
---|
738 | int k;
|
---|
739 | for (k = 0; k < W; k++)
|
---|
740 | data = (data << 8) ^
|
---|
741 | crc_big_table[(data >> ((W - 1) << 3)) & 0xff];
|
---|
742 | return data;
|
---|
743 | }
|
---|
744 |
|
---|
745 | #endif
|
---|
746 |
|
---|
747 | /* ========================================================================= */
|
---|
748 | unsigned long ZEXPORT crc32_z(crc, buf, len)
|
---|
749 | unsigned long crc;
|
---|
750 | const unsigned char FAR *buf;
|
---|
751 | z_size_t len;
|
---|
752 | {
|
---|
753 | /* Return initial CRC, if requested. */
|
---|
754 | if (buf == Z_NULL) return 0;
|
---|
755 |
|
---|
756 | #ifdef DYNAMIC_CRC_TABLE
|
---|
757 | once(&made, make_crc_table);
|
---|
758 | #endif /* DYNAMIC_CRC_TABLE */
|
---|
759 |
|
---|
760 | /* Pre-condition the CRC */
|
---|
761 | crc = (~crc) & 0xffffffff;
|
---|
762 |
|
---|
763 | #ifdef W
|
---|
764 |
|
---|
765 | /* If provided enough bytes, do a braided CRC calculation. */
|
---|
766 | if (len >= N * W + W - 1) {
|
---|
767 | z_size_t blks;
|
---|
768 | z_word_t const *words;
|
---|
769 | unsigned endian;
|
---|
770 | int k;
|
---|
771 |
|
---|
772 | /* Compute the CRC up to a z_word_t boundary. */
|
---|
773 | while (len && ((z_size_t)buf & (W - 1)) != 0) {
|
---|
774 | len--;
|
---|
775 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
776 | }
|
---|
777 |
|
---|
778 | /* Compute the CRC on as many N z_word_t blocks as are available. */
|
---|
779 | blks = len / (N * W);
|
---|
780 | len -= blks * N * W;
|
---|
781 | words = (z_word_t const *)buf;
|
---|
782 |
|
---|
783 | /* Do endian check at execution time instead of compile time, since ARM
|
---|
784 | processors can change the endianess at execution time. If the
|
---|
785 | compiler knows what the endianess will be, it can optimize out the
|
---|
786 | check and the unused branch. */
|
---|
787 | endian = 1;
|
---|
788 | if (*(unsigned char *)&endian) {
|
---|
789 | /* Little endian. */
|
---|
790 |
|
---|
791 | z_crc_t crc0;
|
---|
792 | z_word_t word0;
|
---|
793 | #if N > 1
|
---|
794 | z_crc_t crc1;
|
---|
795 | z_word_t word1;
|
---|
796 | #if N > 2
|
---|
797 | z_crc_t crc2;
|
---|
798 | z_word_t word2;
|
---|
799 | #if N > 3
|
---|
800 | z_crc_t crc3;
|
---|
801 | z_word_t word3;
|
---|
802 | #if N > 4
|
---|
803 | z_crc_t crc4;
|
---|
804 | z_word_t word4;
|
---|
805 | #if N > 5
|
---|
806 | z_crc_t crc5;
|
---|
807 | z_word_t word5;
|
---|
808 | #endif
|
---|
809 | #endif
|
---|
810 | #endif
|
---|
811 | #endif
|
---|
812 | #endif
|
---|
813 |
|
---|
814 | /* Initialize the CRC for each braid. */
|
---|
815 | crc0 = crc;
|
---|
816 | #if N > 1
|
---|
817 | crc1 = 0;
|
---|
818 | #if N > 2
|
---|
819 | crc2 = 0;
|
---|
820 | #if N > 3
|
---|
821 | crc3 = 0;
|
---|
822 | #if N > 4
|
---|
823 | crc4 = 0;
|
---|
824 | #if N > 5
|
---|
825 | crc5 = 0;
|
---|
826 | #endif
|
---|
827 | #endif
|
---|
828 | #endif
|
---|
829 | #endif
|
---|
830 | #endif
|
---|
831 |
|
---|
832 | /*
|
---|
833 | Process the first blks-1 blocks, computing the CRCs on each braid
|
---|
834 | independently.
|
---|
835 | */
|
---|
836 | while (--blks) {
|
---|
837 | /* Load the word for each braid into registers. */
|
---|
838 | word0 = crc0 ^ words[0];
|
---|
839 | #if N > 1
|
---|
840 | word1 = crc1 ^ words[1];
|
---|
841 | #if N > 2
|
---|
842 | word2 = crc2 ^ words[2];
|
---|
843 | #if N > 3
|
---|
844 | word3 = crc3 ^ words[3];
|
---|
845 | #if N > 4
|
---|
846 | word4 = crc4 ^ words[4];
|
---|
847 | #if N > 5
|
---|
848 | word5 = crc5 ^ words[5];
|
---|
849 | #endif
|
---|
850 | #endif
|
---|
851 | #endif
|
---|
852 | #endif
|
---|
853 | #endif
|
---|
854 | words += N;
|
---|
855 |
|
---|
856 | /* Compute and update the CRC for each word. The loop should
|
---|
857 | get unrolled. */
|
---|
858 | crc0 = crc_braid_table[0][word0 & 0xff];
|
---|
859 | #if N > 1
|
---|
860 | crc1 = crc_braid_table[0][word1 & 0xff];
|
---|
861 | #if N > 2
|
---|
862 | crc2 = crc_braid_table[0][word2 & 0xff];
|
---|
863 | #if N > 3
|
---|
864 | crc3 = crc_braid_table[0][word3 & 0xff];
|
---|
865 | #if N > 4
|
---|
866 | crc4 = crc_braid_table[0][word4 & 0xff];
|
---|
867 | #if N > 5
|
---|
868 | crc5 = crc_braid_table[0][word5 & 0xff];
|
---|
869 | #endif
|
---|
870 | #endif
|
---|
871 | #endif
|
---|
872 | #endif
|
---|
873 | #endif
|
---|
874 | for (k = 1; k < W; k++) {
|
---|
875 | crc0 ^= crc_braid_table[k][(word0 >> (k << 3)) & 0xff];
|
---|
876 | #if N > 1
|
---|
877 | crc1 ^= crc_braid_table[k][(word1 >> (k << 3)) & 0xff];
|
---|
878 | #if N > 2
|
---|
879 | crc2 ^= crc_braid_table[k][(word2 >> (k << 3)) & 0xff];
|
---|
880 | #if N > 3
|
---|
881 | crc3 ^= crc_braid_table[k][(word3 >> (k << 3)) & 0xff];
|
---|
882 | #if N > 4
|
---|
883 | crc4 ^= crc_braid_table[k][(word4 >> (k << 3)) & 0xff];
|
---|
884 | #if N > 5
|
---|
885 | crc5 ^= crc_braid_table[k][(word5 >> (k << 3)) & 0xff];
|
---|
886 | #endif
|
---|
887 | #endif
|
---|
888 | #endif
|
---|
889 | #endif
|
---|
890 | #endif
|
---|
891 | }
|
---|
892 | }
|
---|
893 |
|
---|
894 | /*
|
---|
895 | Process the last block, combining the CRCs of the N braids at the
|
---|
896 | same time.
|
---|
897 | */
|
---|
898 | crc = crc_word(crc0 ^ words[0]);
|
---|
899 | #if N > 1
|
---|
900 | crc = crc_word(crc1 ^ words[1] ^ crc);
|
---|
901 | #if N > 2
|
---|
902 | crc = crc_word(crc2 ^ words[2] ^ crc);
|
---|
903 | #if N > 3
|
---|
904 | crc = crc_word(crc3 ^ words[3] ^ crc);
|
---|
905 | #if N > 4
|
---|
906 | crc = crc_word(crc4 ^ words[4] ^ crc);
|
---|
907 | #if N > 5
|
---|
908 | crc = crc_word(crc5 ^ words[5] ^ crc);
|
---|
909 | #endif
|
---|
910 | #endif
|
---|
911 | #endif
|
---|
912 | #endif
|
---|
913 | #endif
|
---|
914 | words += N;
|
---|
915 | }
|
---|
916 | else {
|
---|
917 | /* Big endian. */
|
---|
918 |
|
---|
919 | z_word_t crc0, word0, comb;
|
---|
920 | #if N > 1
|
---|
921 | z_word_t crc1, word1;
|
---|
922 | #if N > 2
|
---|
923 | z_word_t crc2, word2;
|
---|
924 | #if N > 3
|
---|
925 | z_word_t crc3, word3;
|
---|
926 | #if N > 4
|
---|
927 | z_word_t crc4, word4;
|
---|
928 | #if N > 5
|
---|
929 | z_word_t crc5, word5;
|
---|
930 | #endif
|
---|
931 | #endif
|
---|
932 | #endif
|
---|
933 | #endif
|
---|
934 | #endif
|
---|
935 |
|
---|
936 | /* Initialize the CRC for each braid. */
|
---|
937 | crc0 = byte_swap(crc);
|
---|
938 | #if N > 1
|
---|
939 | crc1 = 0;
|
---|
940 | #if N > 2
|
---|
941 | crc2 = 0;
|
---|
942 | #if N > 3
|
---|
943 | crc3 = 0;
|
---|
944 | #if N > 4
|
---|
945 | crc4 = 0;
|
---|
946 | #if N > 5
|
---|
947 | crc5 = 0;
|
---|
948 | #endif
|
---|
949 | #endif
|
---|
950 | #endif
|
---|
951 | #endif
|
---|
952 | #endif
|
---|
953 |
|
---|
954 | /*
|
---|
955 | Process the first blks-1 blocks, computing the CRCs on each braid
|
---|
956 | independently.
|
---|
957 | */
|
---|
958 | while (--blks) {
|
---|
959 | /* Load the word for each braid into registers. */
|
---|
960 | word0 = crc0 ^ words[0];
|
---|
961 | #if N > 1
|
---|
962 | word1 = crc1 ^ words[1];
|
---|
963 | #if N > 2
|
---|
964 | word2 = crc2 ^ words[2];
|
---|
965 | #if N > 3
|
---|
966 | word3 = crc3 ^ words[3];
|
---|
967 | #if N > 4
|
---|
968 | word4 = crc4 ^ words[4];
|
---|
969 | #if N > 5
|
---|
970 | word5 = crc5 ^ words[5];
|
---|
971 | #endif
|
---|
972 | #endif
|
---|
973 | #endif
|
---|
974 | #endif
|
---|
975 | #endif
|
---|
976 | words += N;
|
---|
977 |
|
---|
978 | /* Compute and update the CRC for each word. The loop should
|
---|
979 | get unrolled. */
|
---|
980 | crc0 = crc_braid_big_table[0][word0 & 0xff];
|
---|
981 | #if N > 1
|
---|
982 | crc1 = crc_braid_big_table[0][word1 & 0xff];
|
---|
983 | #if N > 2
|
---|
984 | crc2 = crc_braid_big_table[0][word2 & 0xff];
|
---|
985 | #if N > 3
|
---|
986 | crc3 = crc_braid_big_table[0][word3 & 0xff];
|
---|
987 | #if N > 4
|
---|
988 | crc4 = crc_braid_big_table[0][word4 & 0xff];
|
---|
989 | #if N > 5
|
---|
990 | crc5 = crc_braid_big_table[0][word5 & 0xff];
|
---|
991 | #endif
|
---|
992 | #endif
|
---|
993 | #endif
|
---|
994 | #endif
|
---|
995 | #endif
|
---|
996 | for (k = 1; k < W; k++) {
|
---|
997 | crc0 ^= crc_braid_big_table[k][(word0 >> (k << 3)) & 0xff];
|
---|
998 | #if N > 1
|
---|
999 | crc1 ^= crc_braid_big_table[k][(word1 >> (k << 3)) & 0xff];
|
---|
1000 | #if N > 2
|
---|
1001 | crc2 ^= crc_braid_big_table[k][(word2 >> (k << 3)) & 0xff];
|
---|
1002 | #if N > 3
|
---|
1003 | crc3 ^= crc_braid_big_table[k][(word3 >> (k << 3)) & 0xff];
|
---|
1004 | #if N > 4
|
---|
1005 | crc4 ^= crc_braid_big_table[k][(word4 >> (k << 3)) & 0xff];
|
---|
1006 | #if N > 5
|
---|
1007 | crc5 ^= crc_braid_big_table[k][(word5 >> (k << 3)) & 0xff];
|
---|
1008 | #endif
|
---|
1009 | #endif
|
---|
1010 | #endif
|
---|
1011 | #endif
|
---|
1012 | #endif
|
---|
1013 | }
|
---|
1014 | }
|
---|
1015 |
|
---|
1016 | /*
|
---|
1017 | Process the last block, combining the CRCs of the N braids at the
|
---|
1018 | same time.
|
---|
1019 | */
|
---|
1020 | comb = crc_word_big(crc0 ^ words[0]);
|
---|
1021 | #if N > 1
|
---|
1022 | comb = crc_word_big(crc1 ^ words[1] ^ comb);
|
---|
1023 | #if N > 2
|
---|
1024 | comb = crc_word_big(crc2 ^ words[2] ^ comb);
|
---|
1025 | #if N > 3
|
---|
1026 | comb = crc_word_big(crc3 ^ words[3] ^ comb);
|
---|
1027 | #if N > 4
|
---|
1028 | comb = crc_word_big(crc4 ^ words[4] ^ comb);
|
---|
1029 | #if N > 5
|
---|
1030 | comb = crc_word_big(crc5 ^ words[5] ^ comb);
|
---|
1031 | #endif
|
---|
1032 | #endif
|
---|
1033 | #endif
|
---|
1034 | #endif
|
---|
1035 | #endif
|
---|
1036 | words += N;
|
---|
1037 | crc = byte_swap(comb);
|
---|
1038 | }
|
---|
1039 |
|
---|
1040 | /*
|
---|
1041 | Update the pointer to the remaining bytes to process.
|
---|
1042 | */
|
---|
1043 | buf = (unsigned char const *)words;
|
---|
1044 | }
|
---|
1045 |
|
---|
1046 | #endif /* W */
|
---|
1047 |
|
---|
1048 | /* Complete the computation of the CRC on any remaining bytes. */
|
---|
1049 | while (len >= 8) {
|
---|
1050 | len -= 8;
|
---|
1051 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1052 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1053 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1054 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1055 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1056 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1057 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1058 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1059 | }
|
---|
1060 | while (len) {
|
---|
1061 | len--;
|
---|
1062 | crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
|
---|
1063 | }
|
---|
1064 |
|
---|
1065 | /* Return the CRC, post-conditioned. */
|
---|
1066 | return crc ^ 0xffffffff;
|
---|
1067 | }
|
---|
1068 |
|
---|
1069 | #endif
|
---|
1070 |
|
---|
1071 | /* ========================================================================= */
|
---|
1072 | unsigned long ZEXPORT crc32(crc, buf, len)
|
---|
1073 | unsigned long crc;
|
---|
1074 | const unsigned char FAR *buf;
|
---|
1075 | uInt len;
|
---|
1076 | {
|
---|
1077 | return crc32_z(crc, buf, len);
|
---|
1078 | }
|
---|
1079 |
|
---|
1080 | /* ========================================================================= */
|
---|
1081 | uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
|
---|
1082 | uLong crc1;
|
---|
1083 | uLong crc2;
|
---|
1084 | z_off64_t len2;
|
---|
1085 | {
|
---|
1086 | #ifdef DYNAMIC_CRC_TABLE
|
---|
1087 | once(&made, make_crc_table);
|
---|
1088 | #endif /* DYNAMIC_CRC_TABLE */
|
---|
1089 | return multmodp(x2nmodp(len2, 3), crc1) ^ (crc2 & 0xffffffff);
|
---|
1090 | }
|
---|
1091 |
|
---|
1092 | /* ========================================================================= */
|
---|
1093 | uLong ZEXPORT crc32_combine(crc1, crc2, len2)
|
---|
1094 | uLong crc1;
|
---|
1095 | uLong crc2;
|
---|
1096 | z_off_t len2;
|
---|
1097 | {
|
---|
1098 | return crc32_combine64(crc1, crc2, (z_off64_t)len2);
|
---|
1099 | }
|
---|
1100 |
|
---|
1101 | /* ========================================================================= */
|
---|
1102 | uLong ZEXPORT crc32_combine_gen64(len2)
|
---|
1103 | z_off64_t len2;
|
---|
1104 | {
|
---|
1105 | #ifdef DYNAMIC_CRC_TABLE
|
---|
1106 | once(&made, make_crc_table);
|
---|
1107 | #endif /* DYNAMIC_CRC_TABLE */
|
---|
1108 | return x2nmodp(len2, 3);
|
---|
1109 | }
|
---|
1110 |
|
---|
1111 | /* ========================================================================= */
|
---|
1112 | uLong ZEXPORT crc32_combine_gen(len2)
|
---|
1113 | z_off_t len2;
|
---|
1114 | {
|
---|
1115 | return crc32_combine_gen64((z_off64_t)len2);
|
---|
1116 | }
|
---|
1117 |
|
---|
1118 | /* ========================================================================= */
|
---|
1119 | uLong ZEXPORT crc32_combine_op(crc1, crc2, op)
|
---|
1120 | uLong crc1;
|
---|
1121 | uLong crc2;
|
---|
1122 | uLong op;
|
---|
1123 | {
|
---|
1124 | return multmodp(op, crc1) ^ (crc2 & 0xffffffff);
|
---|
1125 | }
|
---|