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/*
* csum.c Checksum calculation for DECnet routing
*
* 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 (at your option) any later version.
*
* Authors: Christine Caulfield <christine.caulfield@googlemail.com>
*
*/
#include <stdio.h>
unsigned short route_csum(unsigned char *buf, int start, int end)
{
unsigned int sum = 1; /* Starting value for Phase IV */
int i;
for (i=start; i<end; i++, i++)
{
sum += buf[i] + (buf[i+1]<<8);
}
sum = (sum>>16) + (sum&0xFFFF);
sum = (sum>>16) + (sum&0xFFFF);
return (unsigned short)sum;
}
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