From: Rémy Oudompheng <oudomphe@phare.normalesup.org>
Date: Tue, 3 Jul 2012 22:38:01 +0000 (+0200)
Subject: math/rand: avoid use of math.Pow in tests.
X-Git-Tag: go1.1rc2~2835
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=1a0a09dafecddf2b63befda53aa5e54d74ce19e1;p=gostls13.git

math/rand: avoid use of math.Pow in tests.

The use of math.Pow for mere squaring can be extremely
slow on soft-float ARM. Even on systems with hardware
floating-point, a speedup in test duration is observed.

On amd64
Before: ok      math/rand       2.009s
After:  ok      math/rand       0.340s

Fixes #3740.

R=dave, golang-dev, r, r
CC=golang-dev
https://golang.org/cl/6348061
---

diff --git a/src/pkg/math/rand/rand_test.go b/src/pkg/math/rand/rand_test.go
index bbd44e3f8b..4d3abdb606 100644
--- a/src/pkg/math/rand/rand_test.go
+++ b/src/pkg/math/rand/rand_test.go
@@ -57,16 +57,13 @@ func (this *statsResults) checkSimilarDistribution(expected *statsResults) error
 
 func getStatsResults(samples []float64) *statsResults {
 	res := new(statsResults)
-	var sum float64
-	for i := range samples {
-		sum += samples[i]
+	var sum, squaresum float64
+	for _, s := range samples {
+		sum += s
+		squaresum += s * s
 	}
 	res.mean = sum / float64(len(samples))
-	var devsum float64
-	for i := range samples {
-		devsum += math.Pow(samples[i]-res.mean, 2)
-	}
-	res.stddev = math.Sqrt(devsum / float64(len(samples)))
+	res.stddev = math.Sqrt(squaresum/float64(len(samples)) - res.mean*res.mean)
 	return res
 }