code: func (d *MyDecimal) Compare(to *MyDecimal) int {
  	if d.negative == to.negative {
  		cmp, err := doSub(d, to, nil)
  		terror.Log(errors.Trace(err))
  		return cmp
  	}
  	if d.negative {
  		return -1
  	}
  	return 1
  }
docs: // Compare compares one decimal to another, returns -1/0/1.