code: func add2(a, b, carry int32) (int32, int32) {
  	sum := int64(a) + int64(b) + int64(carry)
  	if sum >= wordBase {
  		carry = 1
  		sum -= wordBase
  	} else {
  		carry = 0
  	}
  
  	if sum >= wordBase {
  		sum -= wordBase
  		carry++
  	}
  	return int32(sum), carry
  }
docs: // add2 adds a and b and carry, returns the sum and new carry.
  // It is only used in DecimalMul.