code: func DecimalAdd(from1, from2, to *MyDecimal) error {
  	to.resultFrac = myMaxInt8(from1.resultFrac, from2.resultFrac)
  	if from1.negative == from2.negative {
  		return doAdd(from1, from2, to)
  	}
  	_, err := doSub(from1, from2, to)
  	return err
  }
docs: // DecimalAdd adds two decimals, sets the result to 'to'.
  // Note: DO NOT use `from1` or `from2` as `to` since the metadata
  // of `to` may be changed during evaluating.