BZip2BitInputStream.java

/*
 * Copyright (c) 2011 Matthew Francis
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package org.xbib.io.compress.bzip2;

import java.io.IOException;
import java.io.InputStream;


/**
 * An InputStream wrapper that allows the reading of single bit booleans, unary numbers, bit
 * strings of arbitrary length (up to 24 bits), and bit aligned 32-bit integers. A single byte at a
 * time is read from the wrapped stream when more bits are required
 */
public class BZip2BitInputStream {

    /**
     * The stream from which bits are read
     */
    private final InputStream inputStream;

    /**
     * A buffer of bits read from the input stream that have not yet been returned
     */
    private int bitBuffer;

    /**
     * The number of bits currently buffered in {@link #bitBuffer}
     */
    private int bitCount;

    /**
     * Reads a single bit from the wrapped input stream
     *
     * @return {@code true} if the bit read was {@code 1}, otherwise {@code false}
     * @throws java.io.IOException if no more bits are available in the input stream
     */
    public boolean readBoolean() throws IOException {
        int bitBuffer = this.bitBuffer;
        int bitCount = this.bitCount;
        if (bitCount > 0) {
            bitCount--;
        } else {
            int byteRead = this.inputStream.read();
            if (byteRead < 0) {
                throw new BZip2Exception("Insufficient data");
            }
            bitBuffer = (bitBuffer << 8) | byteRead;
            bitCount += 7;
            this.bitBuffer = bitBuffer;
        }
        this.bitCount = bitCount;
        return ((bitBuffer & (1 << bitCount))) != 0;
    }

    /**
     * Reads a zero-terminated unary number from the wrapped input stream
     *
     * @return The unary number
     * @throws java.io.IOException if no more bits are available in the input stream
     */
    public int readUnary() throws IOException {

        int bitBuffer = this.bitBuffer;
        int bitCount = this.bitCount;
        int unaryCount = 0;
        for (; ; ) {
            if (bitCount > 0) {
                bitCount--;
            } else {
                int byteRead = this.inputStream.read();
                if (byteRead < 0) {
                    throw new BZip2Exception("Insufficient data");
                }
                bitBuffer = (bitBuffer << 8) | byteRead;
                bitCount += 7;
            }
            if (((bitBuffer & (1 << bitCount))) == 0) {
                this.bitBuffer = bitBuffer;
                this.bitCount = bitCount;
                return unaryCount;
            }
            unaryCount++;
        }
    }

    /**
     * Reads up to 24 bits from the wrapped input stream
     *
     * @param count The number of bits to read (maximum 24)
     * @return The bits requested, right-aligned within the integer
     * @throws java.io.IOException if more bits are requested than are available in the input stream
     */
    public int readBits(final int count) throws IOException {
        int bitBuffer = this.bitBuffer;
        int bitCount = this.bitCount;
        if (bitCount < count) {
            while (bitCount < count) {
                int byteRead = this.inputStream.read();
                if (byteRead < 0) {
                    throw new BZip2Exception("Insufficient data");
                }
                bitBuffer = (bitBuffer << 8) | byteRead;
                bitCount += 8;
            }
            this.bitBuffer = bitBuffer;
        }
        bitCount -= count;
        this.bitCount = bitCount;
        return (bitBuffer >>> bitCount) & ((1 << count) - 1);
    }


    /**
     * Reads 32 bits of input as an integer
     *
     * @return The integer read
     * @throws java.io.IOException if 32 bits are not available in the input stream
     */
    public int readInteger() throws IOException {
        return (readBits(16) << 16) | (readBits(16));
    }

    /**
     * @param inputStream The InputStream to wrap
     */
    public BZip2BitInputStream(final InputStream inputStream) {
        this.inputStream = inputStream;
    }
}