1 /* 2 * COPYRIGHT (C) 1986 Gary S. Brown. You may use this program, or 3 * code or tables extracted from it, as desired without restriction. 4 * 5 * First, the polynomial itself and its table of feedback terms. The 6 * polynomial is 7 * 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+X^0 8 * 9 * Note that we take it "backwards" and put the highest-order term in 10 * the lowest-order bit. The X^32 term is "implied"; the LSB is the 11 * X^31 term, etc. The X^0 term (usually shown as "+1") results in 12 * the MSB being 1 13 * 14 * Note that the usual hardware shift register implementation, which 15 * is what we're using (we're merely optimizing it by doing eight-bit 16 * chunks at a time) shifts bits into the lowest-order term. In our 17 * implementation, that means shifting towards the right. Why do we 18 * do it this way? Because the calculated CRC must be transmitted in 19 * order from highest-order term to lowest-order term. UARTs transmit 20 * characters in order from LSB to MSB. By storing the CRC this way 21 * we hand it to the UART in the order low-byte to high-byte; the UART 22 * sends each low-bit to hight-bit; and the result is transmission bit 23 * by bit from highest- to lowest-order term without requiring any bit 24 * shuffling on our part. Reception works similarly 25 * 26 * The feedback terms table consists of 256, 32-bit entries. Notes 27 * 28 * The table can be generated at runtime if desired; code to do so 29 * is shown later. It might not be obvious, but the feedback 30 * terms simply represent the results of eight shift/xor opera 31 * tions for all combinations of data and CRC register values 32 * 33 * The values must be right-shifted by eight bits by the "updcrc 34 * logic; the shift must be u_(bring in zeroes). On some 35 * hardware you could probably optimize the shift in assembler by 36 * using byte-swap instructions 37 * polynomial $edb88320 38 */ 39 40 41 #include "includes.h" 42 RCSID("$OpenBSD: crc32.c,v 1.8 2000/12/19 23:17:56 markus Exp $"); 43 44 #pragma ident "%Z%%M% %I% %E% SMI" 45 46 #include "crc32.h" 47 48 static u_int crc32_tab[] = { 49 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 50 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 51 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 52 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 53 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 54 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 55 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 56 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 57 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 58 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a, 59 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 60 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 61 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 62 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 63 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e, 64 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, 65 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 66 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 67 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 68 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 69 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 70 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 71 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010, 72 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, 73 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 74 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 75 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 76 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 77 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344, 78 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 79 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 80 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 81 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 82 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c, 83 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 84 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 85 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 86 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 87 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 88 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, 89 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 90 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242, 91 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 92 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 93 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278, 94 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 95 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 96 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, 97 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 98 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 99 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 100 0x2d02ef8d 101 }; 102 103 /* Return a 32-bit CRC of the contents of the buffer. */ 104 105 u_int 106 ssh_crc32(const u_char *s, u_int len) 107 { 108 u_int i; 109 u_int crc32val; 110 111 crc32val = 0; 112 for (i = 0; i < len; i ++) { 113 crc32val = crc32_tab[(crc32val ^ s[i]) & 0xff] ^ (crc32val >> 8); 114 } 115 return crc32val; 116 } 117