code: function readLength() {
      var byte = delta[deltaOffset++];
      var length = byte & 0x7f;
      var shift = 7;
      while (byte & 0x80) {
        byte = delta[deltaOffset++];
        length |= (byte & 0x7f) << shift;
        shift += 7;
      }
      return length;
    }
docs: Read a variable length number our of delta and move the offset.