code: public int writeValue( byte[] buf, int offset, boolean reset )
                             throws IOException {
        if ( size <= 0 ) {
          return 0;
        }
  
        if ( size == 4 ) {
          int checksum = (int) summer.getValue();
          writeIntToBuf(checksum, buf, offset);
        } else {
          throw new IOException( "Unknown Checksum " + type );
        }
        
        if ( reset ) {
          reset();
        }
        
        return size;
      }
docs: Writes the current checksum to a buffer.
  If <i>reset</i> is true, then resets the checksum.
  @return number of bytes written. Will be equal to getChecksumSize();