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1 /* crc32.c -- compute the CRC-32 of a data stream |
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2 * Copyright (C) 1995-1998 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 |
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6 /* @(#) $Id$ */ |
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7 |
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8 #include "zlib.h" |
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9 |
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10 #define local static |
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11 |
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12 #ifdef DYNAMIC_CRC_TABLE |
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13 |
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14 local int crc_table_empty = 1; |
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15 local uLongf crc_table[256]; |
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16 local void make_crc_table OF((void)); |
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17 |
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18 /* |
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19 Generate a table for a byte-wise 32-bit CRC calculation on the polynomial: |
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20 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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21 |
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22 Polynomials over GF(2) are represented in binary, one bit per coefficient, |
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23 with the lowest powers in the most significant bit. Then adding polynomials |
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24 is just exclusive-or, and multiplying a polynomial by x is a right shift by |
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25 one. If we call the above polynomial p, and represent a byte as the |
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26 polynomial q, also with the lowest power in the most significant bit (so the |
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27 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, |
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28 where a mod b means the remainder after dividing a by b. |
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29 |
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30 This calculation is done using the shift-register method of multiplying and |
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31 taking the remainder. The register is initialized to zero, and for each |
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32 incoming bit, x^32 is added mod p to the register if the bit is a one (where |
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33 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by |
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34 x (which is shifting right by one and adding x^32 mod p if the bit shifted |
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35 out is a one). We start with the highest power (least significant bit) of |
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36 q and repeat for all eight bits of q. |
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37 |
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38 The table is simply the CRC of all possible eight bit values. This is all |
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39 the information needed to generate CRC's on data a byte at a time for all |
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40 combinations of CRC register values and incoming bytes. |
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41 */ |
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42 local void make_crc_table() |
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43 { |
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44 uLong c; |
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45 int n, k; |
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46 uLong poly; /* polynomial exclusive-or pattern */ |
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47 /* terms of polynomial defining this crc (except x^32): */ |
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48 static const Byte p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; |
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49 |
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50 /* make exclusive-or pattern from polynomial (0xedb88320L) */ |
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51 poly = 0L; |
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52 for (n = 0; n < sizeof(p)/sizeof(Byte); n++) |
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53 poly |= 1L << (31 - p[n]); |
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54 |
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55 for (n = 0; n < 256; n++) |
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56 { |
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57 c = (uLong)n; |
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58 for (k = 0; k < 8; k++) |
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59 c = c & 1 ? poly ^ (c >> 1) : c >> 1; |
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60 crc_table[n] = c; |
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61 } |
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62 crc_table_empty = 0; |
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63 } |
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64 #else |
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65 /* ======================================================================== |
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66 * Table of CRC-32's of all single-byte values (made by make_crc_table) |
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67 */ |
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68 local const uLongf crc_table[256] = { |
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69 0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L, |
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70 0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L, |
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71 0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L, |
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72 0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL, |
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73 0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L, |
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74 0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L, |
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75 0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L, |
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76 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL, |
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77 0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L, |
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78 0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL, |
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79 0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L, |
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80 0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L, |
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81 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L, |
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82 0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL, |
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83 0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL, |
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84 0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L, |
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85 0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL, |
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86 0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L, |
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87 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L, |
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88 0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L, |
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89 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL, |
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90 0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L, |
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91 0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L, |
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92 0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL, |
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93 0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L, |
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94 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L, |
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95 0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L, |
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96 0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L, |
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97 0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L, |
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98 0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL, |
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99 0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL, |
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100 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L, |
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101 0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L, |
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102 0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL, |
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103 0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL, |
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104 0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L, |
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105 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL, |
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106 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L, |
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107 0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL, |
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108 0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L, |
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109 0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL, |
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110 0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L, |
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111 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L, |
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112 0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL, |
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113 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L, |
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114 0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L, |
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115 0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L, |
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116 0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L, |
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117 0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L, |
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118 0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L, |
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119 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL, |
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120 0x2d02ef8dL |
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121 }; |
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122 #endif |
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123 |
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124 /* ========================================================================= |
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125 * This function can be used by asm versions of crc32() |
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126 */ |
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127 const uLongf * ZEXPORT get_crc_table() |
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128 { |
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129 #ifdef DYNAMIC_CRC_TABLE |
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130 if (crc_table_empty) make_crc_table(); |
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131 #endif |
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132 return (const uLongf *)crc_table; |
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133 } |
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134 |
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135 /* ========================================================================= */ |
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136 #define DO1(buf) crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8); |
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137 #define DO2(buf) DO1(buf); DO1(buf); |
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138 #define DO4(buf) DO2(buf); DO2(buf); |
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139 #define DO8(buf) DO4(buf); DO4(buf); |
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140 |
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141 /* ========================================================================= */ |
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142 uLong ZEXPORT crc32(uLong crc, const Bytef *buf, uInt len) |
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143 { |
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144 if (buf == Z_NULL) return 0L; |
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145 #ifdef DYNAMIC_CRC_TABLE |
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146 if (crc_table_empty) |
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147 make_crc_table(); |
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148 #endif |
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149 crc = crc ^ 0xffffffffL; |
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150 while (len >= 8) |
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151 { |
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152 DO8(buf); |
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153 len -= 8; |
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154 } |
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155 if (len) do { |
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156 DO1(buf); |
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157 } while (--len); |
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158 return crc ^ 0xffffffffL; |
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159 } |