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/*
* kexec: Linux boots Linux
*
* Copyright (C) 2003,2004 Eric Biederman (ebiederm@xmission.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 (version 2 of the License).
*
* 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.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include <stdint.h>
#include <ip_checksum.h>
#include <string.h>
unsigned long compute_ip_checksum(void *addr, unsigned long length)
{
uint16_t *ptr;
unsigned long sum;
unsigned long len;
unsigned long laddr;
/* compute an ip style checksum */
laddr = (unsigned long )addr;
sum = 0;
if (laddr & 1) {
uint16_t buffer;
unsigned char *ptr;
/* copy the first byte into a 2 byte buffer.
* This way automatically handles the endian question
* of which byte (low or high) the last byte goes in.
*/
buffer = 0;
ptr = addr;
memcpy(&buffer, ptr, 1);
sum += buffer;
if (sum > 0xFFFF)
sum -= 0xFFFF;
length -= 1;
addr = ptr +1;
}
len = length >> 1;
ptr = addr;
while (len--) {
sum += *(ptr++);
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
addr = ptr;
if (length & 1) {
uint16_t buffer;
unsigned char *ptr;
/* copy the last byte into a 2 byte buffer.
* This way automatically handles the endian question
* of which byte (low or high) the last byte goes in.
*/
buffer = 0;
ptr = addr;
memcpy(&buffer, ptr, 1);
sum += buffer;
if (sum > 0xFFFF)
sum -= 0xFFFF;
}
return (~sum) & 0xFFFF;
}
unsigned long add_ip_checksums(unsigned long offset, unsigned long sum, unsigned long new)
{
unsigned long checksum;
sum = ~sum & 0xFFFF;
new = ~new & 0xFFFF;
if (offset & 1) {
/* byte swap the sum if it came from an odd offset
* since the computation is endian independant this
* works.
*/
new = ((new >> 8) & 0xff) | ((new << 8) & 0xff00);
}
checksum = sum + new;
if (checksum > 0xFFFF) {
checksum -= 0xFFFF;
}
return (~checksum) & 0xFFFF;
}
unsigned long negate_ip_checksum(unsigned long sum)
{
sum = ~sum & 0xFFFF;
sum = 0xFFFF - sum;
return ~sum & 0xFFFF;
}
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