1 /* updcrc(3), crc(1) - calculate crc polynomials
3 * Calculate, intelligently, the CRC of a dataset incrementally given a
4 * buffer full at a time.
7 * newcrc = updcrc( oldcrc, bufadr, buflen )
8 * unsigned int oldcrc, buflen;
11 * Compiling with -DTEST creates a program to print the CRC of stdin to stdout.
12 * Compile with -DMAKETAB to print values for crctab to stdout. If you change
13 * the CRC polynomial parameters, be sure to do this and change
14 * crctab's initial value.
17 * Regards the data stream as an integer whose MSB is the MSB of the first
18 * byte recieved. This number is 'divided' (using xor instead of subtraction)
19 * by the crc-polynomial P.
20 * XMODEM does things a little differently, essentially treating the LSB of
21 * the first data byte as the MSB of the integer. Define SWAPPED to make
22 * things behave in this manner.
24 * Author: Mark G. Mendel, 7/86
25 * UUCP: ihnp4!umn-cs!hyper!mark, GEnie: mgm
32 /* The CRC polynomial.
33 * These 4 values define the crc-polynomial.
34 * If you change them, you must change crctab[]'s initial value to what is
35 * printed by initcrctab() [see 'compile with -DMAKETAB' above].
37 /* Value used by: CCITT XMODEM ARC */
38 #define P 0x1021 /* the poly: 0x1021 0x1021 A001 */
39 #define INIT_CRC 0L /* init value: -1 0 0 */
40 /*#define SWAPPED /* bit order: undef defined defined */
41 #define W 16 /* bits in CRC:16 16 16 */
43 /* data type that holds a W-bit unsigned integer */
45 # define WTYPE unsigned short
47 # define WTYPE u_int32_t
50 /* the number of bits per char: don't change it. */
53 static WTYPE crctab[1<<B] = /* as calculated by initcrctab() */ {
54 0x0, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
55 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
56 0x1231, 0x210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
57 0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
58 0x2462, 0x3443, 0x420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
59 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
60 0x3653, 0x2672, 0x1611, 0x630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
61 0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
62 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x840, 0x1861, 0x2802, 0x3823,
63 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
64 0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0xa50, 0x3a33, 0x2a12,
65 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
66 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0xc60, 0x1c41,
67 0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
68 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0xe70,
69 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
70 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
71 0x1080, 0xa1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
72 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
73 0x2b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
74 0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
75 0x34e2, 0x24c3, 0x14a0, 0x481, 0x7466, 0x6447, 0x5424, 0x4405,
76 0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
77 0x26d3, 0x36f2, 0x691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
78 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
79 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x8e1, 0x3882, 0x28a3,
80 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
81 0x4a75, 0x5a54, 0x6a37, 0x7a16, 0xaf1, 0x1ad0, 0x2ab3, 0x3a92,
82 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
83 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0xcc1,
84 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
85 0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0xed1, 0x1ef0,
89 updcrc( icrc, icp, icnt )
94 register WTYPE crc = icrc;
95 register unsigned char *cp = icp;
96 register int cnt = icnt;
100 crc = (crc<<B) ^ crctab[(crc>>(W-B)) ^ *cp++];
102 crc = (crc>>B) ^ crctab[(crc & ((1<<B)-1)) ^ *cp++];
123 for( b = 0; b <= (1<<B)-1; ++b ) {
125 for( v = b<<(W-B), i = B; --i >= 0; )
126 v = v & ((WTYPE)1<<(W-1)) ? (v<<1)^P : v<<1;
128 for( v = b, i = B; --i >= 0; )
129 v = v & 1 ? (v>>1)^P : v>>1;
133 printf( "0x%lx,", v & ((1L<<W)-1L));
162 if( (fd = open( av[1], O_RDONLY )) < 0 ) {
166 crc = crc2 = INIT_CRC;
168 while( (nr = read( fd, buf, MAXBUF )) > 0 ) {
169 crc = updcrc( crc, buf, nr );
175 printf( "%lx\n", crc );
179 /* tack one's complement of crc onto data stream, and
180 continue crc calculation. Should get a constant (magic number)
181 dependent only on P, not the data.
184 for( nr = W-B; nr >= 0; nr -= B ) {
185 buf[0] = (crc2 >> nr);
186 crc = updcrc(crc, buf, 1);
189 /* crc should now equal magic */
190 buf[0] = buf[1] = buf[2] = buf[3] = 0;
191 printf( "magic test: %lx =?= %lx\n", crc, updcrc(-1, buf, W/B));