code: public byte[] toBytes(/*INOUT*/ byte[] buff) {
      assert buff != null;
      assert(buff.length == 8) : "buff argument not an array of length 8";
      long val = _fp;
      for (int i = 0; i < buff.length; i++) {
        buff[i] = (byte) (val & 0xFF);
        val >>>= 8;
      }
      return buff;
    }
docs: Returns the value of this fingerprint as an 8-byte array.
  Unlike {@link #toBytes()}, this variant does not perform
  an allocation. Instead, the client passes in a buffer into
  which the fingerprint value is written. This can be used
  to get the values of a set of fingerprints without having
  to perform an allocation for each one.
  
  @param buff
  The buffer into which the bytes will be written. This
  array is required to be non-null and exactly 8 bytes in
  length. This buffer is returned.