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Android/Desktop/iOS/HTML5 game development framework

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/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * Licensed 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 com.badlogic.gdx.utils.compression.rangecoder;

import java.io.IOException;

public class Decoder {
	static final int kTopMask = ~((1 << 24) - 1);

	static final int kNumBitModelTotalBits = 11;
	static final int kBitModelTotal = (1 << kNumBitModelTotalBits);
	static final int kNumMoveBits = 5;

	int Range;
	int Code;

	java.io.InputStream Stream;

	public final void SetStream (java.io.InputStream stream) {
		Stream = stream;
	}

	public final void ReleaseStream () {
		Stream = null;
	}

	public final void Init () throws IOException {
		Code = 0;
		Range = -1;
		for (int i = 0; i < 5; i++)
			Code = (Code << 8) | Stream.read();
	}

	public final int DecodeDirectBits (int numTotalBits) throws IOException {
		int result = 0;
		for (int i = numTotalBits; i != 0; i--) {
			Range >>>= 1;
			int t = ((Code - Range) >>> 31);
			Code -= Range & (t - 1);
			result = (result << 1) | (1 - t);

			if ((Range & kTopMask) == 0) {
				Code = (Code << 8) | Stream.read();
				Range <<= 8;
			}
		}
		return result;
	}

	public int DecodeBit (short[] probs, int index) throws IOException {
		int prob = probs[index];
		int newBound = (Range >>> kNumBitModelTotalBits) * prob;
		if ((Code ^ 0x80000000) < (newBound ^ 0x80000000)) {
			Range = newBound;
			probs[index] = (short)(prob + ((kBitModelTotal - prob) >>> kNumMoveBits));
			if ((Range & kTopMask) == 0) {
				Code = (Code << 8) | Stream.read();
				Range <<= 8;
			}
			return 0;
		} else {
			Range -= newBound;
			Code -= newBound;
			probs[index] = (short)(prob - ((prob) >>> kNumMoveBits));
			if ((Range & kTopMask) == 0) {
				Code = (Code << 8) | Stream.read();
				Range <<= 8;
			}
			return 1;
		}
	}

	public static void InitBitModels (short[] probs) {
		for (int i = 0; i < probs.length; i++)
			probs[i] = (kBitModelTotal >>> 1);
	}
}