JAVA实现位流缓冲区--更改

import java.io.InputStream;

public final class BitStream {
	private  final int RESELEN = 4096;//默认缓冲区大小
	private  InputStream  in;//输入流
	private byte[] bitBuf;//提高处理 缓冲区
	private int bitPos; //位位置
	private int bytePos;//字节位置
	private int endPos; //bitBuf已填入的字节数  

	public BitStream(InputStream  in) {
		
		this.in = in;
		bitBuf = new byte[RESELEN + 4]; // 长度不小于(最大帧长)  
		
	}
	
	public BitStream(InputStream  in,int size) {
		
		this.in = in;
		bitBuf = new byte[size + 4]; // 长度不小于size(最大帧长)  
	}
	/**
	 * <p>
	 * 简述:向bitBuf添加len字节,RESELEN后尾部要空出4字节用于32bit的"2级缓冲". 
	 * </p>
	 */
	public int append(int len) {
		if (len + endPos > RESELEN) {
			//将缓冲区bytePos及之后的字节移动到缓冲区首  
			System.arraycopy(bitBuf, bytePos, bitBuf, 0, endPos
					- bytePos);
			endPos -= bytePos;
			bitPos = bytePos = 0;
		}
		try {
			if(in.read(bitBuf, endPos, len)==-1)
				return -1;  
		} catch (Exception e) {
			e.printStackTrace();
			return -1;
		}

		endPos += len;
		return len;
	}
	/**
	 * <p>
	 * 简述:重置 bitstream
	 * </p>
	 */
	public void resetIndex() {
		bytePos = bitPos = endPos = 0;
	}
	/**
	 * <p>
	 * 简述:从缓冲区bitBuf读取1 bit
	 * </p>
	 */
	public int get1Bit() {
		int bit = bitBuf[bytePos] << bitPos;
		bit >>= 7;
		bit &= 0x1;
		bitPos++;
		bytePos += bitPos >> 3;
		bitPos &= 0x7;
		return bit;
	}
	/**
	 * 
	 * <p>
	 * 简述:2 <= n <= 17 
	 * </p>
	 */
	public int getBits17(int n) {
		int iret = bitBuf[bytePos];
		iret <<= 8;
		iret |= bitBuf[bytePos + 1] & 0xff;
		iret <<= 8;
		iret |= bitBuf[bytePos + 2] & 0xff;
		iret <<= bitPos;
		iret &= 0xffffff; // 高8位置0;  
		iret >>= 24 - n;
		bitPos += n;
		bytePos += bitPos >> 3;
		bitPos &= 0x7;
		return iret;
	}

 http://lfp001.iteye.com/blog/412745

评论

1 楼 sblig 2011-11-22  

/**
	 * 
	 * <p>
	 * 简述:2 <= n <= 33 
	 * </p>
	 */
	public int getBits33(int n) {
		int iret = bitBuf[bytePos];
		iret <<= 8;
		iret |= bitBuf[bytePos + 1] & 0xff;
		iret <<= 8;
		iret |= bitBuf[bytePos + 2] & 0xff;
		iret <<= 8;
		iret |= bitBuf[bytePos + 3] & 0xff;
		iret <<= bitPos;
		iret &= 0xffffffff; // 高32位置0;  
		iret >>= 32 - n;
		bitPos += n;
		bytePos += bitPos >> 3;
		bitPos &= 0x7;
		return iret;
	}

	/**
	 * 
	 * <p>
	 * 简述: 2<= n <= 9 
	 * </p>
	 */
	public int getBits9(int n) {
		int iret = bitBuf[bytePos];
		iret <<= 8;
		iret |= bitBuf[bytePos + 1] & 0xff;
		iret <<= bitPos;
		iret &= 0xffff; // 高16位置0;  
		iret >>= 16 - n;
		bitPos += n;
		bytePos += bitPos >> 3;
		bitPos &= 0x7;
		return iret;
	}
	public int getBytePos() {
		return bytePos;
	}
	public int getBuffBytes() {
		return endPos;
	}
	public int getBitPos() {
		return bitPos;
	}
	/** 
	 * 返回值是0-255的无符号整数 
	 */
	public int get1Byte() {
		return bitBuf[bytePos++] & 0xff;
	}
	/**
	 * <p>
	 * 简述: 回跳 n 个位
	 * </p>
	 */
	public void backBits(int n) {
		bitPos -= n;
		bytePos += bitPos >> 3;
		bitPos &= 0x7;
	}
	/**
	 * <p>
	 * 简述:跳转 nbtyes 个字节
	 * </p>
	 */
	public void skipBytes(int nbytes) {
		bytePos += nbytes;
		bitPos = 0;
	}
}