93 lines
2.0 KiB
Go
93 lines
2.0 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// This file prints execution times for the Mul benchmark
|
|
// given different Karatsuba thresholds. The result may be
|
|
// used to manually fine-tune the threshold constant. The
|
|
// results are somewhat fragile; use repeated runs to get
|
|
// a clear picture.
|
|
|
|
// Usage: gotest -calibrate
|
|
|
|
package big
|
|
|
|
import (
|
|
"flag"
|
|
"fmt"
|
|
"testing"
|
|
"time"
|
|
)
|
|
|
|
|
|
var calibrate = flag.Bool("calibrate", false, "run calibration test")
|
|
|
|
|
|
// measure returns the time to run f
|
|
func measure(f func()) int64 {
|
|
const N = 100
|
|
start := time.Nanoseconds()
|
|
for i := N; i > 0; i-- {
|
|
f()
|
|
}
|
|
stop := time.Nanoseconds()
|
|
return (stop - start) / N
|
|
}
|
|
|
|
|
|
func computeThresholds() {
|
|
fmt.Printf("Multiplication times for varying Karatsuba thresholds\n")
|
|
fmt.Printf("(run repeatedly for good results)\n")
|
|
|
|
// determine Tk, the work load execution time using basic multiplication
|
|
karatsubaThreshold = 1e9 // disable karatsuba
|
|
Tb := measure(benchmarkMulLoad)
|
|
fmt.Printf("Tb = %dns\n", Tb)
|
|
|
|
// thresholds
|
|
n := 8 // any lower values for the threshold lead to very slow multiplies
|
|
th1 := -1
|
|
th2 := -1
|
|
|
|
var deltaOld int64
|
|
for count := -1; count != 0; count-- {
|
|
// determine Tk, the work load execution time using Karatsuba multiplication
|
|
karatsubaThreshold = n // enable karatsuba
|
|
Tk := measure(benchmarkMulLoad)
|
|
|
|
// improvement over Tb
|
|
delta := (Tb - Tk) * 100 / Tb
|
|
|
|
fmt.Printf("n = %3d Tk = %8dns %4d%%", n, Tk, delta)
|
|
|
|
// determine break-even point
|
|
if Tk < Tb && th1 < 0 {
|
|
th1 = n
|
|
fmt.Print(" break-even point")
|
|
}
|
|
|
|
// determine diminishing return
|
|
if 0 < delta && delta < deltaOld && th2 < 0 {
|
|
th2 = n
|
|
fmt.Print(" diminishing return")
|
|
}
|
|
deltaOld = delta
|
|
|
|
fmt.Println()
|
|
|
|
// trigger counter
|
|
if th1 >= 0 && th2 >= 0 && count < 0 {
|
|
count = 20 // this many extra measurements after we got both thresholds
|
|
}
|
|
|
|
n++
|
|
}
|
|
}
|
|
|
|
|
|
func TestCalibrate(t *testing.T) {
|
|
if *calibrate {
|
|
computeThresholds()
|
|
}
|
|
}
|