1 /* $OpenBSD: crc32.c,v 1.4 1998/05/30 02:20:50 mickey Exp $ */ 2 /* crc32.c -- compute the CRC-32 of a data stream 3 * Copyright (C) 1995-1996 Mark Adler 4 * For conditions of distribution and use, see copyright notice in zlib.h 5 */ 6 7 8 #include "zlib.h" 9 10 #ifndef local 11 #define local static 12 #endif 13 14 #ifdef DYNAMIC_CRC_TABLE 15 16 local int crc_table_empty = 1; 17 local uLongf crc_table[256]; 18 local void make_crc_table OF((void)); 19 20 /* 21 Generate a table for a byte-wise 32-bit CRC calculation on the polynomial: 22 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. 23 24 Polynomials over GF(2) are represented in binary, one bit per coefficient, 25 with the lowest powers in the most significant bit. Then adding polynomials 26 is just exclusive-or, and multiplying a polynomial by x is a right shift by 27 one. If we call the above polynomial p, and represent a byte as the 28 polynomial q, also with the lowest power in the most significant bit (so the 29 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, 30 where a mod b means the remainder after dividing a by b. 31 32 This calculation is done using the shift-register method of multiplying and 33 taking the remainder. The register is initialized to zero, and for each 34 incoming bit, x^32 is added mod p to the register if the bit is a one (where 35 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by 36 x (which is shifting right by one and adding x^32 mod p if the bit shifted 37 out is a one). We start with the highest power (least significant bit) of 38 q and repeat for all eight bits of q. 39 40 The table is simply the CRC of all possible eight bit values. This is all 41 the information needed to generate CRC's on data a byte at a time for all 42 combinations of CRC register values and incoming bytes. 43 */ 44 local void make_crc_table() 45 { 46 uLong c; 47 int n, k; 48 uLong poly; /* polynomial exclusive-or pattern */ 49 /* terms of polynomial defining this crc (except x^32): */ 50 static const Byte p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; 51 52 /* make exclusive-or pattern from polynomial (0xedb88320L) */ 53 poly = 0L; 54 for (n = 0; n < sizeof(p)/sizeof(Byte); n++) 55 poly |= 1L << (31 - p[n]); 56 57 for (n = 0; n < 256; n++) 58 { 59 c = (uLong)n; 60 for (k = 0; k < 8; k++) 61 c = c & 1 ? poly ^ (c >> 1) : c >> 1; 62 crc_table[n] = c; 63 } 64 crc_table_empty = 0; 65 } 66 #else 67 /* ======================================================================== 68 * Table of CRC-32's of all single-byte values (made by make_crc_table) 69 */ 70 local uLongf crc_table[256] = { 71 0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L, 72 0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L, 73 0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L, 74 0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL, 75 0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L, 76 0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L, 77 0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L, 78 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL, 79 0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L, 80 0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL, 81 0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L, 82 0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L, 83 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L, 84 0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL, 85 0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL, 86 0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L, 87 0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL, 88 0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L, 89 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L, 90 0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L, 91 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL, 92 0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L, 93 0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L, 94 0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL, 95 0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L, 96 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L, 97 0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L, 98 0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L, 99 0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L, 100 0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL, 101 0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL, 102 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L, 103 0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L, 104 0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL, 105 0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL, 106 0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L, 107 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL, 108 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L, 109 0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL, 110 0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L, 111 0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL, 112 0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L, 113 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L, 114 0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL, 115 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L, 116 0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L, 117 0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L, 118 0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L, 119 0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L, 120 0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L, 121 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL, 122 0x2d02ef8dL 123 }; 124 #endif 125 126 /* ========================================================================= 127 * This function can be used by asm versions of crc32() 128 */ 129 uLongf *get_crc_table() 130 { 131 #ifdef DYNAMIC_CRC_TABLE 132 if (crc_table_empty) make_crc_table(); 133 #endif 134 return (uLongf *)crc_table; 135 } 136 137 /* ========================================================================= */ 138 #define DO1(buf) crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8); 139 #define DO2(buf) DO1(buf); DO1(buf); 140 #define DO4(buf) DO2(buf); DO2(buf); 141 #define DO8(buf) DO4(buf); DO4(buf); 142 143 /* ========================================================================= */ 144 uLong crc32(crc, buf, len) 145 uLong crc; 146 const Bytef *buf; 147 uInt len; 148 { 149 if (buf == Z_NULL) return 0L; 150 #ifdef DYNAMIC_CRC_TABLE 151 if (crc_table_empty) 152 make_crc_table(); 153 #endif 154 crc = crc ^ 0xffffffffL; 155 while (len >= 8) 156 { 157 DO8(buf); 158 len -= 8; 159 } 160 if (len) do { 161 DO1(buf); 162 } while (--len); 163 return crc ^ 0xffffffffL; 164 } 165