BZip2BitOutputStream.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.OutputStream;


/**
 * <p>An OutputStream wrapper that allows the writing 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 written to the wrapped stream when sufficient bits have been accumulated
 */
public class BZip2BitOutputStream {

    /**
     * The stream to which bits are written
     */
    private final OutputStream outputStream;

    /**
     * A buffer of bits waiting to be written to the output stream
     */
    private int bitBuffer;

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


    /**
     * Writes a single bit to the wrapped output stream
     *
     * @param value The bit to write
     * @throws java.io.IOException if an error occurs writing to the stream
     */
    public void writeBoolean(final boolean value) throws IOException {

        int bitCount = this.bitCount + 1;
        int bitBuffer = this.bitBuffer | ((value ? 1 : 0) << (32 - bitCount));

        if (bitCount == 8) {
            this.outputStream.write(bitBuffer >>> 24);
            bitBuffer = 0;
            bitCount = 0;
        }

        this.bitBuffer = bitBuffer;
        this.bitCount = bitCount;

    }


    /**
     * Writes a zero-terminated unary number to the wrapped output stream
     *
     * @param value The number to write (must be non-negative)
     * @throws java.io.IOException if an error occurs writing to the stream
     */
    public void writeUnary(int value) throws IOException {

        while (value-- > 0) {
            writeBoolean(true);
        }
        writeBoolean(false);

    }


    /**
     * Writes up to 24 bits to the wrapped output stream
     *
     * @param count The number of bits to write (maximum 24)
     * @param value The bits to write
     * @throws java.io.IOException if an error occurs writing to the stream
     */
    public void writeBits(final int count, final int value) throws IOException {

        int bitCount = this.bitCount;
        int bitBuffer = this.bitBuffer | ((value << (32 - count)) >>> bitCount);
        bitCount += count;

        while (bitCount >= 8) {
            this.outputStream.write(bitBuffer >>> 24);
            bitBuffer <<= 8;
            bitCount -= 8;
        }

        this.bitBuffer = bitBuffer;
        this.bitCount = bitCount;

    }


    /**
     * Writes an integer as 32 bits of output
     *
     * @param value The integer to write
     * @throws java.io.IOException if an error occurs writing to the stream
     */
    public void writeInteger(final int value) throws IOException {

        writeBits(16, (value >>> 16) & 0xffff);
        writeBits(16, value & 0xffff);

    }


    /**
     * Writes any remaining bits to the output stream, zero padding to a whole byte as required
     *
     * @throws java.io.IOException if an error occurs writing to the stream
     */
    public void flush() throws IOException {

        if (this.bitCount > 0) {
            writeBits(8 - this.bitCount, 0);
        }

    }


    /**
     * @param outputStream The OutputStream to wrap
     */
    public BZip2BitOutputStream(final OutputStream outputStream) {

        this.outputStream = outputStream;

    }

}