import java.util.zip.*;

public class ParityChecksum implements Checksum {

  private long checksum = 0;

  public void update(int b) {  
    int numOneBits = 0;
    for (int i = 1; i < 256; i *= 2) {
      if ((b & i) != 0) numOneBits++;
    } 
    checksum = (checksum + numOneBits) % 2;
  }
  
  public void update(byte data[], int offset, int length) {  
    for (int i = offset; i < offset+length; i++) {
      this.update(data[i]);
    }
  }
  
  public long getValue() {
    return checksum;
  }

  public void reset() {
    checksum = 0;
  }
}