194 lines
5.8 KiB
Plaintext
194 lines
5.8 KiB
Plaintext
/* updcrc(3), crc(1) - calculate crc polynomials
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*
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* Calculate, intelligently, the CRC of a dataset incrementally given a
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* buffer full at a time.
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*
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* Usage:
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* newcrc = updcrc( oldcrc, bufadr, buflen )
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* unsigned int oldcrc, buflen;
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* char *bufadr;
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*
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* Compiling with -DTEST creates a program to print the CRC of stdin to stdout.
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* Compile with -DMAKETAB to print values for crctab to stdout. If you change
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* the CRC polynomial parameters, be sure to do this and change
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* crctab's initial value.
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*
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* Notes:
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* Regards the data stream as an integer whose MSB is the MSB of the first
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* byte recieved. This number is 'divided' (using xor instead of subtraction)
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* by the crc-polynomial P.
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* XMODEM does things a little differently, essentially treating the LSB of
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* the first data byte as the MSB of the integer. Define SWAPPED to make
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* things behave in this manner.
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*
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* Author: Mark G. Mendel, 7/86
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* UUCP: ihnp4!umn-cs!hyper!mark, GEnie: mgm
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*/
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/* The CRC polynomial.
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* These 4 values define the crc-polynomial.
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* If you change them, you must change crctab[]'s initial value to what is
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* printed by initcrctab() [see 'compile with -DMAKETAB' above].
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*/
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/* Value used by: CITT XMODEM ARC */
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#define P 0xA001 /* the poly: 0x1021 0x1021 A001 */
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#define INIT_CRC 0L /* init value: -1 0 0 */
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#define SWAPPED /* bit order: undef defined defined */
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#define W 16 /* bits in CRC:16 16 16 */
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/* data type that holds a W-bit unsigned integer */
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#if W <= 16
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# define WTYPE unsigned short
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#else
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# define WTYPE unsigned long
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#endif
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/* the number of bits per char: don't change it. */
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#define B 8
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static WTYPE crctab[1<<B] = /* as calculated by initcrctab() */ {
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0x0, 0xc0c1, 0xc181, 0x140, 0xc301, 0x3c0, 0x280, 0xc241,
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0xc601, 0x6c0, 0x780, 0xc741, 0x500, 0xc5c1, 0xc481, 0x440,
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0xcc01, 0xcc0, 0xd80, 0xcd41, 0xf00, 0xcfc1, 0xce81, 0xe40,
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0xa00, 0xcac1, 0xcb81, 0xb40, 0xc901, 0x9c0, 0x880, 0xc841,
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0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40,
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0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
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0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641,
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0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,
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0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240,
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0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,
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0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41,
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0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
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0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41,
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0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,
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0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640,
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0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,
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0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240,
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0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
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0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41,
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0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,
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0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41,
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0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,
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0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640,
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0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
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0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241,
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0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,
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0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40,
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0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,
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0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40,
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0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
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0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641,
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0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040,
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} ;
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WTYPE
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updcrc( icrc, icp, icnt )
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WTYPE icrc;
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unsigned char *icp;
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int icnt;
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{
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register WTYPE crc = icrc;
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register unsigned char *cp = icp;
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register int cnt = icnt;
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while( cnt-- ) {
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#ifndef SWAPPED
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crc = (crc<<B) ^ crctab[(crc>>(W-B)) ^ *cp++];
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#else
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crc = (crc>>B) ^ crctab[(crc & ((1<<B)-1)) ^ *cp++];
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#endif SWAPPED
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}
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return( crc );
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}
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#ifdef MAKETAB
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#include <stdio.h>
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main()
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{
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initcrctab();
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}
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initcrctab()
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{
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register int b, i;
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WTYPE v;
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for( b = 0; b <= (1<<B)-1; ++b ) {
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#ifndef SWAPPED
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for( v = b<<(W-B), i = B; --i >= 0; )
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v = v & ((WTYPE)1<<(W-1)) ? (v<<1)^P : v<<1;
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#else
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for( v = b, i = B; --i >= 0; )
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v = v & 1 ? (v>>1)^P : v>>1;
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#endif
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crctab[b] = v;
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printf( "0x%lx,", v & ((1L<<W)-1L));
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if( (b&7) == 7 )
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printf("\n" );
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else
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printf(" ");
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}
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}
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#endif
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#ifdef TEST
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#include <stdio.h>
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#include <fcntl.h>
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#define MAXBUF 4096
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main( ac, av )
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int ac; char **av;
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{
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int fd;
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int nr;
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int i;
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char buf[MAXBUF];
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WTYPE crc, crc2;
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fd = 0;
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if( ac > 1 )
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if( (fd = open( av[1], O_RDONLY )) < 0 ) {
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perror( av[1] );
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exit( -1 );
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}
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crc = crc2 = INIT_CRC;
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while( (nr = read( fd, buf, MAXBUF )) > 0 ) {
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crc = updcrc( crc, buf, nr );
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}
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if( nr != 0 )
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perror( "reading" );
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else {
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printf( "%lx\n", crc );
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}
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#ifdef MAGICCHECK
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/* tack one's complement of crc onto data stream, and
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continue crc calculation. Should get a constant (magic number)
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dependent only on P, not the data.
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*/
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crc2 = crc ^ -1L;
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for( nr = W-B; nr >= 0; nr -= B ) {
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buf[0] = (crc2 >> nr);
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crc = updcrc(crc, buf, 1);
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}
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/* crc should now equal magic */
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buf[0] = buf[1] = buf[2] = buf[3] = 0;
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printf( "magic test: %lx =?= %lx\n", crc, updcrc(-1, buf, W/B));
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#endif MAGICCHECK
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}
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#endif
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****************************************************************************
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