func measureMul(th int) (tBig, tFFT time.Duration) {
	bigLoad := func(b *testing.B) { benchmarkMulBig(b, th, th) }
	fftLoad := func(b *testing.B) { benchmarkMulFFT(b, th, th) }
	res1 := testing.Benchmark(bigLoad)
	res2 := testing.Benchmark(fftLoad)
	tBig = time.Duration(res1.NsPerOp())
	tFFT = time.Duration(res2.NsPerOp())
	return
}
measureMul benchmarks math/big versus FFT for a given input size
(in bits).
package bigfft
import (
	"flag"
	"fmt"
	"testing"
	"time"
)
var calibrate = flag.Bool("calibrate", false, "run calibration test")