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/*
* RangeDecoder
*
* Authors: Lasse Collin <lasse.collin@tukaani.org>
* Igor Pavlov <http://7-zip.org/>
*
* This file has been put into the public domain.
* You can do whatever you want with this file.
*/
package org.tukaani.xz.rangecoder;
import java.io.DataInputStream;
import java.io.IOException;
public abstract class RangeDecoder extends RangeCoder {
int range = 0;
int code = 0;
public abstract void normalize() throws IOException;
public int decodeBit(short[] probs, int index) throws IOException {
normalize();
int prob = probs[index];
int bound = (range >>> BIT_MODEL_TOTAL_BITS) * prob;
int bit;
// Compare code and bound as if they were unsigned 32-bit integers.
if ((code ^ 0x80000000) < (bound ^ 0x80000000)) {
range = bound;
probs[index] = (short)(
prob + ((BIT_MODEL_TOTAL - prob) >>> MOVE_BITS));
bit = 0;
} else {
range -= bound;
code -= bound;
probs[index] = (short)(prob - (prob >>> MOVE_BITS));
bit = 1;
}
return bit;
}
public int decodeBitTree(short[] probs) throws IOException {
int symbol = 1;
do {
symbol = (symbol << 1) | decodeBit(probs, symbol);
} while (symbol < probs.length);
return symbol - probs.length;
}
public int decodeReverseBitTree(short[] probs) throws IOException {
int symbol = 1;
int i = 0;
int result = 0;
do {
int bit = decodeBit(probs, symbol);
symbol = (symbol << 1) | bit;
result |= bit << i++;
} while (symbol < probs.length);
return result;
}
public int decodeDirectBits(int count) throws IOException {
int result = 0;
do {
normalize();
range >>>= 1;
int t = (code - range) >>> 31;
code -= range & (t - 1);
result = (result << 1) | (1 - t);
} while (--count != 0);
return result;
}
}
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