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Diffstat (limited to 'src/math/big/calibrate_test.go')
-rw-r--r-- | src/math/big/calibrate_test.go | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/src/math/big/calibrate_test.go b/src/math/big/calibrate_test.go new file mode 100644 index 000000000..f69ffbf5c --- /dev/null +++ b/src/math/big/calibrate_test.go @@ -0,0 +1,88 @@ +// 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: go test -run=TestCalibrate -calibrate + +package big + +import ( + "flag" + "fmt" + "testing" + "time" +) + +var calibrate = flag.Bool("calibrate", false, "run calibration test") + +func karatsubaLoad(b *testing.B) { + BenchmarkMul(b) +} + +// measureKaratsuba returns the time to run a Karatsuba-relevant benchmark +// given Karatsuba threshold th. +func measureKaratsuba(th int) time.Duration { + th, karatsubaThreshold = karatsubaThreshold, th + res := testing.Benchmark(karatsubaLoad) + karatsubaThreshold = th + return time.Duration(res.NsPerOp()) +} + +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 + Tb := measureKaratsuba(1e9) // th == 1e9 => Karatsuba multiplication disabled + fmt.Printf("Tb = %10s\n", Tb) + + // thresholds + th := 4 + th1 := -1 + th2 := -1 + + var deltaOld time.Duration + for count := -1; count != 0 && th < 128; count-- { + // determine Tk, the work load execution time using Karatsuba multiplication + Tk := measureKaratsuba(th) + + // improvement over Tb + delta := (Tb - Tk) * 100 / Tb + + fmt.Printf("th = %3d Tk = %10s %4d%%", th, Tk, delta) + + // determine break-even point + if Tk < Tb && th1 < 0 { + th1 = th + fmt.Print(" break-even point") + } + + // determine diminishing return + if 0 < delta && delta < deltaOld && th2 < 0 { + th2 = th + fmt.Print(" diminishing return") + } + deltaOld = delta + + fmt.Println() + + // trigger counter + if th1 >= 0 && th2 >= 0 && count < 0 { + count = 10 // this many extra measurements after we got both thresholds + } + + th++ + } +} + +func TestCalibrate(t *testing.T) { + if *calibrate { + computeThresholds() + } +} |