/*
* $Id$
*
* Copyright (C) 2003-2015 JNode.org
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; If not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
package org.jnode.net.ipv4;
import org.jnode.net.SocketBuffer;
/**
* @author epr
*/
public class IPv4Utils {
/**
* Calculate the checksum of the given header
*
* @param skbuf
* @param start
* @param length
* @return The calculated checksum
*/
public static int calcChecksum(SocketBuffer skbuf, int start, int length) {
return calcChecksum(skbuf, start, length, ~0);
}
/**
* Calculate the checksum of the given header
*
* @param skbuf
* @param start
* @param length
* @param initialValue Result from a previous call to calcChecksum. Use when
* to blocks are concatenated
* @return The calculated checksum
*/
public static int calcChecksum(SocketBuffer skbuf, int start, int length, int initialValue) {
final int size = skbuf.getSize();
int chsum = ~initialValue;
for (int i = 0; i < length; i += 2) {
final int v;
if (i + 1 >= size) {
v = (skbuf.get(start + i) << 8);
} else {
v = skbuf.get16(start + i);
}
chsum += v;
if ((chsum & 0xffff0000) != 0) {
chsum++;
chsum &= 0xffff;
}
}
return (short) (~chsum);
}
}