1/* 2 * $Id: updcrc.c,v 1.5 2009-10-13 22:55:36 didg Exp $ 3 * 4 * updcrc(3), crc(1) - calculate crc polynomials 5 * 6 * Calculate, intelligently, the CRC of a dataset incrementally given a 7 * buffer full at a time. 8 * 9 * Usage: 10 * newcrc = updcrc( oldcrc, bufadr, buflen ) 11 * unsigned int oldcrc, buflen; 12 * char *bufadr; 13 * 14 * Compiling with -DTEST creates a program to print the CRC of stdin to stdout. 15 * Compile with -DMAKETAB to print values for crctab to stdout. If you change 16 * the CRC polynomial parameters, be sure to do this and change 17 * crctab's initial value. 18 * 19 * Notes: 20 * Regards the data stream as an integer whose MSB is the MSB of the first 21 * byte recieved. This number is 'divided' (using xor instead of subtraction) 22 * by the crc-polynomial P. 23 * XMODEM does things a little differently, essentially treating the LSB of 24 * the first data byte as the MSB of the integer. Define SWAPPED to make 25 * things behave in this manner. 26 * 27 * Author: Mark G. Mendel, 7/86 28 * UUCP: ihnp4!umn-cs!hyper!mark, GEnie: mgm 29 */ 30 31#ifdef HAVE_CONFIG_H 32#include "config.h" 33#endif /* HAVE_CONFIG_H */ 34 35#include "updcrc.h" 36 37/* The CRC polynomial. 38 * These 4 values define the crc-polynomial. 39 * If you change them, you must change crctab[]'s initial value to what is 40 * printed by initcrctab() [see 'compile with -DMAKETAB' above]. 41 */ 42 /* Value used by: CCITT XMODEM ARC */ 43#define P 0x1021 /* the poly: 0x1021 0x1021 A001 */ 44#define INIT_CRC 0L /* init value: -1 0 0 */ 45#if 0 46#define SWAPPED /* bit order: undef defined defined */ 47#endif /* 0 */ 48 /* the number of bits per char: don't change it. */ 49#define B 8 50 51static WTYPE crctab[1<<B] = /* as calculated by initcrctab() */ { 520x0, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 530x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 540x1231, 0x210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6, 550x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 560x2462, 0x3443, 0x420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485, 570xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d, 580x3653, 0x2672, 0x1611, 0x630, 0x76d7, 0x66f6, 0x5695, 0x46b4, 590xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 600x48c4, 0x58e5, 0x6886, 0x78a7, 0x840, 0x1861, 0x2802, 0x3823, 610xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 620x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0xa50, 0x3a33, 0x2a12, 630xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a, 640x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0xc60, 0x1c41, 650xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49, 660x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0xe70, 670xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, 680x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f, 690x1080, 0xa1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067, 700x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, 710x2b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, 720xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d, 730x34e2, 0x24c3, 0x14a0, 0x481, 0x7466, 0x6447, 0x5424, 0x4405, 740xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c, 750x26d3, 0x36f2, 0x691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634, 760xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab, 770x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x8e1, 0x3882, 0x28a3, 780xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a, 790x4a75, 0x5a54, 0x6a37, 0x7a16, 0xaf1, 0x1ad0, 0x2ab3, 0x3a92, 800xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 810x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0xcc1, 820xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 830x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0xed1, 0x1ef0, 84} ; 85 86WTYPE 87updcrc(WTYPE icrc, unsigned char *icp, int icnt) 88{ 89 register WTYPE crc = icrc; 90 register unsigned char *cp = icp; 91 register int cnt = icnt; 92 93 while( cnt-- ) { 94#ifndef SWAPPED 95 crc = (crc<<B) ^ crctab[(crc>>(W-B)) ^ *cp++]; 96#else /* SWAPPED */ 97 crc = (crc>>B) ^ crctab[(crc & ((1<<B)-1)) ^ *cp++]; 98#endif /* SWAPPED */ 99 } 100 101 return( crc ); 102} 103 104#ifdef MAKETAB 105 106#include <stdio.h> 107int main(void) 108{ 109 initcrctab(); 110} 111 112void initcrctab(void) 113{ 114 register int b, i; 115 WTYPE v; 116 117 118 for( b = 0; b <= (1<<B)-1; ++b ) { 119#ifndef SWAPPED 120 for( v = b<<(W-B), i = B; --i >= 0; ) 121 v = v & ((WTYPE)1<<(W-1)) ? (v<<1)^P : v<<1; 122#else 123 for( v = b, i = B; --i >= 0; ) 124 v = v & 1 ? (v>>1)^P : v>>1; 125#endif 126 crctab[b] = v; 127 128 printf( "0x%lx,", v & ((1L<<W)-1L)); 129 if( (b&7) == 7 ) 130 printf("\n" ); 131 else 132 printf(" "); 133 } 134} 135#endif /* MAKETAB */ 136 137#ifdef TEST 138 139#include <stdio.h> 140#include <fcntl.h> 141 142#define MAXBUF 4096 143 144 145 146main( int ac, char **av) 147{ 148 int fd; 149 int nr; 150 int i; 151 char buf[MAXBUF]; 152 WTYPE crc, crc2; 153 154 fd = 0; 155 if( ac > 1 ) 156 if( (fd = open( av[1], O_RDONLY )) < 0 ) { 157 perror( av[1] ); 158 exit( -1 ); 159 } 160 crc = crc2 = INIT_CRC; 161 162 while( (nr = read( fd, buf, MAXBUF )) > 0 ) { 163 crc = updcrc( crc, buf, nr ); 164 } 165 166 if( nr != 0 ) 167 perror( "reading" ); 168 else { 169 printf( "%lx\n", crc ); 170 } 171 172#ifdef MAGICCHECK 173 /* tack one's complement of crc onto data stream, and 174 continue crc calculation. Should get a constant (magic number) 175 dependent only on P, not the data. 176 */ 177 crc2 = crc ^ -1L; 178 for( nr = W-B; nr >= 0; nr -= B ) { 179 buf[0] = (crc2 >> nr); 180 crc = updcrc(crc, buf, 1); 181 } 182 183 /* crc should now equal magic */ 184 buf[0] = buf[1] = buf[2] = buf[3] = 0; 185 printf( "magic test: %lx =?= %lx\n", crc, updcrc(-1, buf, W/B)); 186#endif /* MAGICCHECK */ 187} 188 189#endif /* TEST */ 190