BitInputStream.java Source code

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Here is the source code for BitInputStream.java

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/*
 * @(#)$Id$
 *
 * Copyright 2006-2008 Makoto YUI
 *
 * 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.
 * 
 * Contributors:
 *     Makoto YUI - initial implementation
 */
//package xbird.util.io;

import java.io.*;

/**
 * 
 * <DIV lang="en"></DIV>
 * <DIV lang="ja"></DIV>
 * 
 * @author Makoto YUI (yuin405+xbird@gmail.com)
 */
public final class BitInputStream extends DataInputStream {

    public static final int MAX_BITS = 31;

    private int leftBits = 0;
    private int byteBuf = 0;

    public BitInputStream(InputStream in) {
        super(in);
    }

    public final boolean readBit() throws IOException {
        if (--leftBits >= 0) {
            return ((byteBuf >>> leftBits) & 1) == 1;
        }
        leftBits = 7;
        byteBuf = in.read();
        if (byteBuf == -1) {
            throw new EOFException("reached end of stream");
        }
        return ((byteBuf >>> 7) & 1) == 1;
    }

    public final int readBits(int n) throws IOException {
        int x = 0;
        while (n > leftBits) {
            n -= leftBits;
            x |= rightBits(leftBits, byteBuf) << n;
            byteBuf = in.read();
            if (byteBuf == -1) {
                throw new EOFException("reached end of stream");
            }
            leftBits = 8;
        }
        leftBits -= n;
        return x | rightBits(n, byteBuf >>> leftBits);
    }

    private static final int rightBits(int n, int x) {
        return x & ((1 << n) - 1);
    }
}