code: func (out *DataOutputImpl) writeNegativeVLong(i int64) error {
  	for (i & ^0x7F) != 0 {
  		err := out.Writer.WriteByte(byte((i & 0x7F) | 0x80))
  		if err != nil {
  			return err
  		}
  		i = int64(uint64(i) >> 7)
  	}
  	return out.Writer.WriteByte(byte(i))
  }
docs: /* write a potentially negative gLong */