| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.imaging.formats.png; |
| |
| // should just use ints, not longs |
| public class PngCrc |
| { |
| /* Table of CRCs of all 8-bit messages. */ |
| private final long crc_table[] = new long[256]; |
| |
| /* Flag: has the table been computed? Initially false. */ |
| private boolean crc_table_computed = false; |
| |
| /* Make the table for a fast CRC. */ |
| private void make_crc_table() |
| { |
| long c; |
| int n, k; |
| |
| for (n = 0; n < 256; n++) |
| { |
| c = n; |
| for (k = 0; k < 8; k++) |
| { |
| if ((c & 1) != 0) |
| |
| c = 0xedb88320L ^ (c >> 1); |
| else |
| c = c >> 1; |
| } |
| 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 final long update_crc(long crc, byte buf[]) |
| { |
| long c = crc; |
| int n; |
| |
| if (!crc_table_computed) |
| make_crc_table(); |
| for (n = 0; n < buf.length; n++) |
| { |
| // Debug.debug("crc[" + n + "]", c + " (" + Long.toHexString(c) + ")"); |
| |
| c = crc_table[(int) ((c ^ buf[n]) & 0xff)] ^ (c >> 8); |
| } |
| return c; |
| } |
| |
| /* Return the CRC of the bytes buf[0..len-1]. */ |
| public final int crc(byte buf[], int len) |
| { |
| return (int) (update_crc(0xffffffffL, buf) ^ 0xffffffffL); |
| } |
| |
| public final long start_partial_crc(byte buf[], int len) |
| { |
| return update_crc(0xffffffffL, buf); |
| } |
| |
| public final long continue_partial_crc(long old_crc, byte buf[], int len) |
| { |
| return update_crc(old_crc, buf); |
| } |
| |
| public final long finish_partial_crc(long old_crc) |
| { |
| return (old_crc ^ 0xffffffffL); |
| } |
| } |