bitwriter.java

如 题

package kava.util;

public class BitWriter {

	  // -- Fields --

	  /** Buffer storing all bits written thus far. */
	  private byte[] buf;

	  /** Byte index into the buffer. */
	  private int index;

	  /** Bit index into current byte of the buffer. */
	  private int bit;


	  // -- Constructors --

	  /** Constructs a new bit writer. */
	  public BitWriter() {
	    this(10);
	  }

	  /** Constructs a new bit writer with the given initial buffer size. */
	  public BitWriter(int size) {
	    buf = new byte[size];
	  }


	  // -- BitWriter API methods --

	  /** Writes the given value using the given number of bits. */
	  public void write(int value, int numBits) {
	    byte[] bits = new byte[numBits];
	    for (int i=0; i<numBits; i++) {
	      bits[i] = (byte) (value & 0x0001);
	      value >>= 1;
	    }
	    for (int i=numBits-1; i>=0; i--) {
	      int b = bits[i] << (7 - bit);
	      buf[index] |= b;
	      bit++;
	      if (bit > 7) {
	        bit = 0;
	        index++;
	        if (index >= buf.length) {
	          // buffer is full; increase the size
	          byte[] newBuf = new byte[buf.length * 2];
	          System.arraycopy(buf, 0, newBuf, 0, buf.length);
	          buf = newBuf;
	        }
	      }
	    }
	  }

	  /** Gets an array containing all bits written thus far. */
	  public byte[] toByteArray() {
	    int size = index;
	    if (bit > 0) size++;
	    byte[] b = new byte[size];
	    System.arraycopy(buf, 0, b, 0, size);
	    return b;
	  }


	  // -- Main method --

	  /** Tests the BitWriter class. */
	  public static void main(String[] args) {
		  BitWriter bw = new BitWriter(128);
		  bw.write(1, 1);
		  bw.write(1, 1);
		  bw.write(1, 1);
		  byte[] data = bw.toByteArray();
		  Util.debug("len = "+data.length +"  "+Util.byteArrayToHexString(data));
	  }
	}