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/******************************************************************************
(c) Eduardo Marcelo Serrat emserrat@geocities.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
Cyclic Redundancy Check
-----------------------
Calculates a 16-bit CRC for use on DECnet for Linux.
The DAP protocol uses the following polynomial:
DAPPOLY(0xE905):
X^16 + X^15 + X^13 + X^7 + X^4 + X^2 + X^1 + X^0
The methods "calc1shift", "calc2shift" and "calc4shift" implements the
one-shift, two-shift and four-shift algorithm options correspondingly.
The "calc4shift" method should be the less CPU Intensive.
Does anybody know which one implements the VAX CRC hardware instruction???
******************************************************************************/
#include "vaxcrc.h"
/*-------------------------------------------------------------------------*/
vaxcrc::vaxcrc(unsigned short poly, unsigned short inicrc)
{
for (int i=0; i < 16; i++)
{
unsigned short tmp=i;
for (int k=0; k < 4; k++)
{
int C = tmp & 1;
tmp = tmp >> 1;
if (C) tmp ^= poly;
}
crc_table[i]=tmp;
}
crc=inicrc;
}
/*-------------------------------------------------------------------------*/
void vaxcrc::setcrc(unsigned short newcrc)
{
crc=newcrc;
}
/*-------------------------------------------------------------------------*/
unsigned short vaxcrc::getcrc()
{
return crc;
}
/*-------------------------------------------------------------------------*/
void vaxcrc::calc1shift(unsigned char *stream, int len)
{
while (len--)
{
crc ^= *stream++;
for (int k=0; k < 8; k++)
crc = (crc >> 1) ^ crc_table[8*(crc & 1)];
}
}
/*-------------------------------------------------------------------------*/
void vaxcrc::calc2shift(unsigned char *stream, int len)
{
while (len--)
{
crc ^= *stream++;
for (int k=0; k < 4; k++)
crc = (crc >> 2) ^ crc_table[4*(crc & 3)];
}
}
/*-------------------------------------------------------------------------*/
void vaxcrc::calc4shift(unsigned char *stream, int len)
{
while (len--)
{
crc ^= *stream++;
for (int k=0; k < 2; k++)
crc = (crc >> 4) ^ crc_table[crc & 15];
}
}
/*-------------------------------------------------------------------------*/
/*-------------------------------------------------------------------------*/
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