Does Multiplication With 1 Affect Query Performance?

Does multiplication with 1 affect query performance?
I have a a stored procedure that converts results to another unit if required.
In alternative 1 below, the results are returned with a separate select statement if no conversion is necessary - in other words, no multiplication with a conversion factor is required. However, the code is not very nice since I need to repeat the select statement again in case a conversion is required, this time including the conversion factor.
Alternative 2 uses cleaner-looking code. The conversion factor is set to 1 if no conversion is required, and a single SELECT statement is used to return the data.

The @factor variable is defined as a float.

I would rather use alternative 2, but I wonder if there is any performance penalty for doing that if no conversion is required since the results are always multiplied with the @factor? Or can SQL server somehow understand that @factor = 1 and no multiplication is required?
--- Alternative 1: ---
IF @fromunit_sid = @tounit_sid
-- Return unconverted results
SELECT ISNULL(ls_totalWaterConsumption,0) AS ls_totalWaterConsumption,
ls_theoreticalWaterConsumption AS ls_theoretical_WaterConsumption,
ls_totalWaterConsumption - ls_theoreticalWaterConsumption AS ls_extra_WaterConsumption
FROM Results WHERE scenario_id = @scenario_id
ELSE
BEGIN
-- Get conversion factor
EXEC getConversionFactor @fromunit_sid, @tounit_sid, @factor OUTPUT

-- Get the converted results
SELECT
ISNULL(ls_totalWaterConsumption * @factor,0) AS ls_totalWaterConsumption,
ls_theoreticalWaterConsumption * @factor AS ls_theoretical_WaterConsumption,
(ls_totalWaterConsumption - ls_theoreticalWaterConsumption) * @factor AS ls_extra_WaterConsumption
FROM Results WHERE scenario_id = @scenario_id
END
 
--- Alternative 2: ---
IF @fromunit_sid = @tounit_sid
SET @factor = 1
ELSE
-- Get conversion factor
EXEC getConversionFactor @fromunit_sid, @tounit_sid, @factor OUTPUT

-- Get the converted results
SELECT
ISNULL(ls_totalWaterConsumption * @factor,0) AS ls_totalWaterConsumption,
ls_theoreticalWaterConsumption * @factor AS ls_theoretical_WaterConsumption,
(ls_totalWaterConsumption - ls_theoreticalWaterConsumption) * @factor AS ls_extra_WaterConsumption
FROM Results WHERE scenario_id = @scenario_id  
And another question: is using an IF function considerably faster than making a call to another stored procedure?
In alternative 2 above I use an IF statement to check if @fromunit_sid = @tounit_sid, and . But in fact the function getConversionFactor that I'm calling does exactly the same thing:  if I pass in identical from- and to-values, it simply returns 1, so I could omit the IF statement completely and just use alternative 3. But is it slower?

--- Alternative 3
-- Get conversion factor
EXEC getConversionFactor @fromunit_sid, @tounit_sid, @factor OUTPUT

-- Get the converted results
...