TransCore MPRX, System Manual

Page: 83 / 208

MPRX
TransCore Proprietary 6–13
unsigned short calccrc(char *message)
{
unsigned short crc = 0;
for ( ; *message != (char)0;+) crc =
updcrc(*message & 0xff, crc);
return (crc)
}
Example 2 shows an example of UPDCRC that does not require a lookup table.
#define BITS_PER_CHAR 8
unsigned short updcrc (unsigned short ch, unsigned short crc)
{
register short counter = BITS_PER_CHAR;
register short temp = crc;
while (--counter >= 0) if
(temp & 0x8000) {
temp <<= 1;
temp += (((ch <<= 1) & 0x0100) != 0);
temp ^= 0x1021;
}
else { temp
<<= 1;
temp += (((ch <<= 1) & 0x0100) != 0);
}
return(temp);
}
Example 3 contains an example of UPDCRC that does require a lookup table.
#define updcrc(cp, crc)( crctab[((crc >> 8) & 255)]^ (crc << 8) ^ cp static
unsigned short crctab [256] = {
0x0000,
0x1021, 0x2042, 0x3063, 0x4048, 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,