3 * updcrc(3), crc(1) - calculate crc polynomials
5 * Calculate, intelligently, the CRC of a dataset incrementally given a
6 * buffer full at a time.
9 * newcrc = updcrc( oldcrc, bufadr, buflen )
10 * unsigned int oldcrc, buflen;
13 * Compiling with -DTEST creates a program to print the CRC of stdin to stdout.
14 * Compile with -DMAKETAB to print values for crctab to stdout. If you change
15 * the CRC polynomial parameters, be sure to do this and change
16 * crctab's initial value.
19 * Regards the data stream as an integer whose MSB is the MSB of the first
20 * byte recieved. This number is 'divided' (using xor instead of subtraction)
21 * by the crc-polynomial P.
22 * XMODEM does things a little differently, essentially treating the LSB of
23 * the first data byte as the MSB of the integer. Define SWAPPED to make
24 * things behave in this manner.
26 * Author: Mark G. Mendel, 7/86
27 * UUCP: ihnp4!umn-cs!hyper!mark, GEnie: mgm
32 #endif /* HAVE_CONFIG_H */
36 /* The CRC polynomial.
37 * These 4 values define the crc-polynomial.
38 * If you change them, you must change crctab[]'s initial value to what is
39 * printed by initcrctab() [see 'compile with -DMAKETAB' above].
41 /* Value used by: CCITT XMODEM ARC */
42 #define P 0x1021 /* the poly: 0x1021 0x1021 A001 */
43 #define INIT_CRC 0L /* init value: -1 0 0 */
45 #define SWAPPED /* bit order: undef defined defined */
47 /* the number of bits per char: don't change it. */
50 static WTYPE crctab[1<<B] = /* as calculated by initcrctab() */ {
51 0x0, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
52 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
53 0x1231, 0x210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
54 0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
55 0x2462, 0x3443, 0x420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
56 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
57 0x3653, 0x2672, 0x1611, 0x630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
58 0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
59 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x840, 0x1861, 0x2802, 0x3823,
60 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
61 0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0xa50, 0x3a33, 0x2a12,
62 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
63 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0xc60, 0x1c41,
64 0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
65 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0xe70,
66 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
67 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
68 0x1080, 0xa1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
69 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
70 0x2b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
71 0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
72 0x34e2, 0x24c3, 0x14a0, 0x481, 0x7466, 0x6447, 0x5424, 0x4405,
73 0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
74 0x26d3, 0x36f2, 0x691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
75 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
76 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x8e1, 0x3882, 0x28a3,
77 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
78 0x4a75, 0x5a54, 0x6a37, 0x7a16, 0xaf1, 0x1ad0, 0x2ab3, 0x3a92,
79 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
80 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0xcc1,
81 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
82 0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0xed1, 0x1ef0,
86 updcrc(WTYPE icrc, unsigned char *icp, int icnt)
88 register WTYPE crc = icrc;
89 register unsigned char *cp = icp;
90 register int cnt = icnt;
94 crc = (crc<<B) ^ crctab[(crc>>(W-B)) ^ *cp++];
96 crc = (crc>>B) ^ crctab[(crc & ((1<<B)-1)) ^ *cp++];
111 void initcrctab(void)
117 for( b = 0; b <= (1<<B)-1; ++b ) {
119 for( v = b<<(W-B), i = B; --i >= 0; )
120 v = v & ((WTYPE)1<<(W-1)) ? (v<<1)^P : v<<1;
122 for( v = b, i = B; --i >= 0; )
123 v = v & 1 ? (v>>1)^P : v>>1;
127 printf( "0x%lx,", v & ((1L<<W)-1L));
145 main( int ac, char **av)
155 if( (fd = open( av[1], O_RDONLY )) < 0 ) {
159 crc = crc2 = INIT_CRC;
161 while( (nr = read( fd, buf, MAXBUF )) > 0 ) {
162 crc = updcrc( crc, buf, nr );
168 printf( "%lx\n", crc );
172 /* tack one's complement of crc onto data stream, and
173 continue crc calculation. Should get a constant (magic number)
174 dependent only on P, not the data.
177 for( nr = W-B; nr >= 0; nr -= B ) {
178 buf[0] = (crc2 >> nr);
179 crc = updcrc(crc, buf, 1);
182 /* crc should now equal magic */
183 buf[0] = buf[1] = buf[2] = buf[3] = 0;
184 printf( "magic test: %lx =?= %lx\n", crc, updcrc(-1, buf, W/B));
185 #endif /* MAGICCHECK */