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/*
* Calculate, intelligently, the CRC of a dataset incrementally given a
* buffer full at a time.
* Initialize crc to 0 for XMODEM, -1 for CCITT.
*
* Usage:
* newcrc = updcrc( oldcrc, bufadr, buflen )
* unsigned int oldcrc, buflen;
* char *bufadr;
*
* Compile with -DTEST to generate program that prints CRC of stdin to stdout.
* Compile with -DMAKETAB to print values for crctab to stdout
*/
/* the CRC polynomial. This is used by XMODEM (almost CCITT).
* If you change P, you must change crctab[]'s initial value to what is
* printed by initcrctab()
*/
#define P 0x1021
/* number of bits in CRC: don't change it. */
#define W 16
/* this the number of bits per char: don't change it. */
#define B 8
static unsigned short crctab[1<<B] = { /* as calculated by initcrctab() */
0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
};
unsigned short updcrc(unsigned short icrc,
unsigned char *icp,
unsigned int icnt )
{
register unsigned short crc = icrc;
register unsigned char *cp = icp;
register unsigned int cnt = icnt;
while( cnt-- )
crc = (crc<<B) ^ crctab[(crc>>(W-B)) ^ *cp++];
return( crc );
}
#ifdef MAKETAB
main()
{
initcrctab();
}
initcrctab()
{
register b, v, i;
for( b = 0; b <= (1<<B)-1; ++b )
{
for( v = b<<(W-B), i = B; --i >= 0; )
v = v&0x8000 ? (v<<1)^P : v<<1;
crctab[b] = v;
printf( "0x%04x,", v & 0xFFFF );
if( (b&7) == 7 )
printf("\n" );
else printf(" ");
}
}
#endif
#ifdef TEST
#include <stdio.h>
#include <fcntl.h>
#define MAXBUF 4096
void main(int argc, char **argv)
{
int fd = 0;
int nr;
char buf[MAXBUF];
unsigned short crc;
if( argc > 1 )
{
if( (fd = open( argv[1], O_RDONLY )) < 0 )
{
perror( argv[1] );
exit( -1 );
}
}
crc = 0;
while( (nr = read( fd, buf, MAXBUF )) > 0 )
crc = updcrc( crc, buf, nr );
printf( "%04x\n", crc );
if( nr != 0 )
perror( "reading" );
}
#endif
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