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/* tnt: Hostmode Terminal for TNC
Copyright (C) 1993 by Mark Wahl
For license details see documentation
Procedures for autobin-checksum (crc.c)
created: Mark Wahl DL4YBG 94/01/17
updated: Mark Wahl DL4YBG 94/01/17
*/
#include "crc.h"
static int crcbit[8] = {
0x9188, 0x48c4, 0x2462, 0x1231, 0x8108, 0x4084, 0x2042, 0x1021
};
static int bittab[8] = { 128, 64, 32, 16, 8, 4, 2, 1 };
static int crctab[256];
void init_crc(void)
{
int i, j;
for (i = 0; i < 256; i++) {
crctab[i] = 0;
for (j = 0; j < 8; j++) {
if ((bittab[j] & i) != 0) {
crctab[i] = crctab[i] ^ crcbit[j];
}
}
}
}
/* calculate checksum for autobin-protocol */
unsigned int calc_crc(unsigned char *buf, int n, unsigned crc)
{
while (--n >= 0)
crc =
(crctab[(crc >> 8)] ^ ((crc << 8) | *buf++)) & 0xffff;
return crc;
}
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