home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Amiga Format CD 6
/
Amiga Format AFCD06 (Nov 1996, Issue 90).iso
/
serious
/
shareware
/
archivers
/
unsit1.5c.amiga
/
src
/
updcrc.c
< prev
Wrap
Text File
|
1991-09-06
|
4KB
|
95 lines
/* updcrc(3), crc(1) - calculate crc polynomials
*
* Calculate, intelligently, the CRC of a dataset incrementally given a
* buffer full at a time.
*
* Usage:
* newcrc = updcrc( oldcrc, bufadr, buflen )
* unsigned int oldcrc, buflen;
* char *bufadr;
*
* Compiling with -DTEST creates a program to print the CRC of stdin to stdout.
* Compile with -DMAKETAB to print values for crctab to stdout. If you change
* the CRC polynomial parameters, be sure to do this and change
* crctab's initial value.
*
* Notes:
* Regards the data stream as an integer whose MSB is the MSB of the first
* byte recieved. This number is 'divided' (using xor instead of subtraction)
* by the crc-polynomial P.
* XMODEM does things a little differently, essentially treating the LSB of
* the first data byte as the MSB of the integer. Define SWAPPED to make
* things behave in this manner.
*
* Author: Mark G. Mendel, 7/86
* UUCP: ihnp4!umn-cs!hyper!mark, GEnie: mgm
*/
/* The CRC polynomial.
* These 4 values define the crc-polynomial.
* If you change them, you must change crctab[]'s initial value to what is
* printed by initcrctab() [see 'compile with -DMAKETAB' above].
*/
/* Value used by: CITT XMODEM ARC */
#define P 0xA001 /* the poly: 0x1021 0x1021 A001 */
#define INIT_CRC 0L /* init value: -1 0 0 */
#define SWAPPED /* bit order: undef defined defined */
#define W 16 /* bits in CRC:16 16 16 */
/* data type that holds a W-bit unsigned integer */
#if W <= 16
# define WTYPE unsigned short
#else
# define WTYPE unsigned long
#endif
/* the number of bits per char: don't change it. */
#define B 8
static WTYPE crctab[1<<B] = {
0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x3c0, 0x0280, 0xc241,
0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,
0xcc01, 0x0cc0, 0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40,
0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0, 0x0880, 0xc841,
0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40,
0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641,
0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,
0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240,
0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,
0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41,
0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41,
0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,
0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640,
0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,
0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240,
0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41,
0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,
0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41,
0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,
0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640,
0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241,
0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,
0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40,
0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,
0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40,
0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641,
0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040,
};
WTYPE updcrc(WTYPE icrc, unsigned char *icp, int icnt ) {
register WTYPE crc = icrc;
register unsigned char *cp = icp;
register int cnt = icnt;
while( cnt-- )
crc = (crc>>B) ^ crctab[(crc & ((1<<B)-1)) ^ *cp++];
return( crc );
}