如何在不使用“ /”和“％”的情况下有效地获得商和余数？

Question

I have implemented a simple function which returns the quotient and remainder when the divisor is the power of 10:

func getQuotientAndRemainder(num int64, digits uint) (int64, int64) {
    divisor := int64(math.Pow(10, float64(digits)))
    if num >= divisor {
        return num / divisor, num % divisor
    } else {
        return 0, num
    }
}

Just curious, except using directly / and % operators, is there any better algorithm to get the the quotient and remainder? Or only in the case when the divisor is the power of 10?

Answer 1

return num / divisor, num % divisor

The "algorithm" is sound and written in arguably the best way possible: expressively. If anything, this part of your code may be overly complicated:

int64(math.Pow(10, float64(digits)))

Converting to and from float64 is arguably sub-optimal. Also, 10 to the power of anything greater than 18 will overflow int64. I suggest you add a sanity check and replace the code with a multiplying loop and measure its performance.

But then: if performance is your concern, just implement it in assembly.