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Pure Java implementation of video/audio codecs and formats

There is a newer version: 0.2.5

package org.jcodec.common.io;

import java.nio.ByteBuffer;

/**
 * This class is part of JCodec ( www.jcodec.org ) This software is distributed
 * under FreeBSD License
 * 
 * Bitstream writer
 * 
 * @author The JCodec project
 * 
 */
public class BitWriter {

    private final ByteBuffer buf;
    private int curInt;
    private int curBit;
    private int initPos;

    public BitWriter(ByteBuffer buf) {
        this.buf = buf;
        initPos = buf.position();
    }

    private BitWriter(ByteBuffer os, int curBit, int curInt, int initPos) {
        this.buf = os;
        this.curBit = curBit;
        this.curInt = curInt;
        this.initPos = initPos;
    }

    public void flush() {
        int toWrite = (curBit + 7) >> 3;
        for (int i = 0; i < toWrite; i++) {
            buf.put((byte) (curInt >>> 24));
            curInt <<= 8;
        }
    }

    private final void putInt(int i) {
        buf.put((byte) (i >>> 24));
        buf.put((byte) (i >> 16));
        buf.put((byte) (i >> 8));
        buf.put((byte) i);
    }

    public final void writeNBit(int value, int n) {
        if (n > 32)
            throw new IllegalArgumentException("Max 32 bit to write");
        if (n == 0)
            return;
        value &= -1 >>> (32 - n);
        if (32 - curBit >= n) {
            curInt |= value << (32 - curBit - n);
            curBit += n;
            if (curBit == 32) {
                putInt(curInt);
                curBit = 0;
                curInt = 0;
            }
        } else {
            int secPart = n - (32 - curBit);
            curInt |= value >>> secPart;
            putInt(curInt);
            curInt = value << (32 - secPart);
            curBit = secPart;
        }
    }

    public void write1Bit(int bit) {
        curInt |= bit << (32 - curBit - 1);
        ++curBit;
        if (curBit == 32) {
            putInt(curInt);
            curBit = 0;
            curInt = 0;
        }
    }

    public int curBit() {
        return curBit & 0x7;
    }

    public BitWriter fork() {
        return new BitWriter(buf.duplicate(), curBit, curInt, initPos);
    }

    public int position() {
        return ((buf.position() - initPos) << 3) + curBit;
    }

    public ByteBuffer getBuffer() {
        return buf;
    }
}