Profiling distance functions in go

CPU and Compiler info

Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz
go version go1.8.3 linux/amd64

distance_func_profiling.go

package main

import (
	"fmt"
	"math"
	"math/rand"
	"time"
)

// octagonal distance with bitshifts, said to have been the distance function
// for the lighting in Diablo II
// taken from:
// http://www.flipcode.com/archives/Fast_Approximate_Distance_Functions.shtml
func approxDistance(a [2]int16, b [2]int16) int16 {
	var min, max int16
	min = int16(a[0] - b[0])
	max = int16(a[1] - b[1])
	if min < 0 {
		min = -min
	}
	if max < 0 {
		max = -max
	}
	if max < min {
		min, max = max, min
	}
	// coefficients equivalent to ( 123/128 * max ) and ( 51/128 * min )
	return (((max << 8) + (max << 3) - (max << 4) - (max << 1) +
		(min << 7) - (min << 5) + (min << 3) - (min << 1)) >> 8)
}

// euclidean distance with sqrt
func distance(a [2]int16, b [2]int16) int16 {
	return int16(
		math.Sqrt(
			float64(
				(a[0]-b[0])*(a[0]-b[0]) +
					(a[0]-b[0])*(a[0]-b[0]))))
}

func ProfileDistanceFunc(f func(a [2]int16, b [2]int16) int16) {
	var N int64 = 1024 * 1024 * 8
	distances := make([]int16, N)
	var sum int64
	for i := int64(0); i < N; i++ {
		a := [2]int16{int16(rand.Intn(100)) - 50, int16(rand.Intn(100)) - 50}
		b := [2]int16{int16(rand.Intn(100)) - 50, int16(rand.Intn(100)) - 50}
		t0 := time.Now()
		distances[i] = approxDistance(a, b)
		sum += time.Since(t0).Nanoseconds()
	}
	fmt.Println(sum / N)
}

func main() {
	rand.Seed(time.Now().UnixNano())
	ProfileDistanceFunc(distance)
	ProfileDistanceFunc(approxDistance)
}

Interestingly, with the CPU and compiler shown, the two functions perform identically.