/*
* Created on Feb 5, 2008
* Created by Olivier Chalouhi
*
* Copyright 2008 Vuze, Inc. All rights reserved.
*
* 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 only.
*
* 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
*/
package com.aelitis.azureus.core.util.png;
import java.nio.ByteBuffer;
import java.security.InvalidParameterException;
public abstract class CRCedChunk extends Chunk{
private byte[] type;
public CRCedChunk(byte[] type) throws InvalidParameterException {
if(type.length != 4) {
throw new InvalidParameterException("type must be of length 4, provided : " + type.length);
}
this.type = type;
}
public byte[] getChunkPayload() {
byte[] contentPayload = getContentPayload();
int length = contentPayload.length;
ByteBuffer buffer = ByteBuffer.allocate(length + 12);
buffer.putInt(length);
buffer.put(type);
buffer.put(contentPayload);
buffer.position(4);
buffer.limit(length + 8);
long crc = crc(buffer);
buffer.limit(length + 12);
buffer.putInt((int)crc);
buffer.position(0);
return buffer.array();
}
public abstract byte[] getContentPayload();
/* Table of CRCs of all 8-bit messages. */
private static long[] crc_table = new long[256];
/* Flag: has the table been computed? Initially false. */
private static boolean crc_table_computed = false;
/* Make the table for a fast CRC. */
private static synchronized void make_crc_table()
{
long c;
int n, k;
for (n = 0; n < 256; n++) {
c = (long) n;
for (k = 0; k < 8; k++) {
if ((c & 1) != 0)
c = 0x0edb88320L ^ ((c >> 1) & 0x0FFFFFFFF);
else
c = c >> 1;
c = c & 0x0FFFFFFFF;
}
crc_table[n] = c;
}
crc_table_computed = true;
}
/* Update a running CRC with the bytes buf[0..len-1]--the CRC
should be initialized to all 1's, and the transmitted value
is the 1's complement of the final running CRC (see the
crc() routine below). */
private static long update_crc(long crc, ByteBuffer buf)
{
long c = crc;
if (!crc_table_computed) {
make_crc_table();
}
while(buf.hasRemaining()) {
c = crc_table[(int) ((c ^ buf.get()) & 0xff)] ^ (c >> 8);
}
return c;
}
/* Return the CRC of the bytes buf[0..len-1]. */
private static long crc(ByteBuffer buf)
{
return update_crc(0xffffffffL, buf) ^ 0xffffffffL;
}
}