bench.txt

<dgryski@kamek[powbench] \ʕ◔ϖ◔ʔ/ > go test -test.bench=.
BenchmarkPolyPow-4    	 5000000	       286 ns/op
BenchmarkPolyFast-4   	100000000	        16.7 ns/op
PASS
ok  	github.com/dgryski/powbench	3.430s

pow.go

package main

import (
	"fmt"
	"math"
)

func poly(x float64, coeffs ...float64) float64 {
	y := coeffs[0]
	for i, c := range coeffs[1:] {
		y += c * math.Pow(x, float64(i))
	}
	return y
}

func polyfast(x float64, coeffs ...float64) float64 {
	y := coeffs[0]
	v := 1.0
	for _, c := range coeffs[1:] {
		y += c * v
		v *= x
	}
	return y
}

func main() {

	var y float64

	y = polyfast(2.5, 0.5, 1, 2, 3, 4, 5, 6)
	fmt.Printf("fast = %+v\n", y)

	y = poly(2.5, 0.5, 1, 2, 3, 4, 5, 6)
	fmt.Printf("pow = %+v\n", y)

}

pow_test.go

package main

import (
	"testing"
)

var sink float64

func BenchmarkPolyPow(b *testing.B) {
	for i := 0; i < b.N; i++ {
		sink += poly(2.5, 1, 2, 3, 4, 5, 6, 7, 8, 10)
	}
}

func BenchmarkPolyFast(b *testing.B) {
	for i := 0; i < b.N; i++ {
		sink += polyfast(2.5, 1, 2, 3, 4, 5, 6, 7, 8, 10)
	}
}