code: private static final void copyBytes(byte[] src, int srcoff, byte[] tgt, 
                                         int tgtoff, int length) {
          if (length < 64) {
              for (int i = srcoff, n = tgtoff; -- length >= 0; ++ i, ++ n) {
                  tgt[n] = src[i];
              }
          } 
          else {
              System.arraycopy(src, srcoff, tgt, tgtoff, length);
          }
      }
docs: Copies the contents of src byte array from offset srcoff to the
  target of tgt byte array at the offset tgtoff.
  @param src source byte array to copy from
  @param srcoff start offset of src to copy from
  @param tgt target byte array to copy to
  @param tgtoff start offset of tgt to copy to
  @param length size of contents to copy