46 lines
1.5 KiB
Java
46 lines
1.5 KiB
Java
/*
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* Copyright 2012 dorkbox, llc
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package dorkbox.cabParser;
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public final class Checksum {
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@SuppressWarnings("fallthrough")
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public static int calculate(byte[] bytes, int currentBlock, int seed) {
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int c1 = (byte) (seed & 0xFF);
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int c2 = (byte) (seed >>> 8 & 0xFF);
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int c3 = (byte) (seed >>> 16 & 0xFF);
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int c4 = (byte) (seed >>> 24 & 0xFF);
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int j = 0;
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int sizeOfBlock = currentBlock >>> 2;
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while (sizeOfBlock-- > 0) {
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c1 = (byte) (c1 ^ bytes[j++]);
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c2 = (byte) (c2 ^ bytes[j++]);
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c3 = (byte) (c3 ^ bytes[j++]);
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c4 = (byte) (c4 ^ bytes[j++]);
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}
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switch (currentBlock & 0x3) {
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case 3 :
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c3 = (byte) (c3 ^ bytes[j++]);
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case 2 :
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c2 = (byte) (c2 ^ bytes[j++]);
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case 1 :
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c1 = (byte) (c1 ^ bytes[j++]);
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}
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return c1 & 0xFF | (c2 & 0xFF) << 8 | (c3 & 0xFF) << 16 | (c4 & 0xFF) << 24;
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}
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}
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