main.go

package cgotest

import (
	//#cgo LDFLAGS: -lm
	//#include <math.h>
	"C"
	"math"
)

func CSin(x float64) float64 {
	return float64(C.sin(C.double(x)))
}

func Sin(x float64) float64 {
	return math.Sin(x)
}

main_test.go

package cgotest

import (
	"math"
	"testing"
)

func BenchmarkCSin(b *testing.B) {
	for i := 0; i < b.N; i++ {
		CSin(float64(i) / 1000.0)
	}
}

func BenchmarkSin(b *testing.B) {
	for i := 0; i < b.N; i++ {
		Sin(float64(i) / 1000.0)
	}
}

func BenchmarkMSin(b *testing.B) {
	for i := 0; i < b.N; i++ {
		math.Sin(float64(i) / 1000.0)
	}
}