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