code review 98170043: runtime: be a lot more lenient on smhasher avalanche test.

runtime: be a lot more lenient on smhasher avalanche test.

Fixes issue 7943

[khr, 2014-05-09 22:28:30]

Hello golang-codereviews@googlegroups.com,

I'd like you to review this change to
https://khr%40golang.org@code.google.com/p/go/

[bradfitz, 2014-05-09 22:34:31]

LGTM
 On May 9, 2014 3:28 PM, <khr@golang.org> wrote:

> Reviewers: golang-codereviews,
>
> Message:
> Hello golang-codereviews@googlegroups.com,
>
> I'd like you to review this change to
> https://khr%40golang.org@code.google.com/p/go/
>
>
> Description:
> runtime: be a lot more lenient on smhasher avalanche test.
>
> Fixes issue 7943
>
> Please review this at https://codereview.appspot.com/98170043/
>
> Affected files (+3, -3 lines):
>   M src/pkg/runtime/hash_test.go
>
>
> Index: src/pkg/runtime/hash_test.go
> ===================================================================
> --- a/src/pkg/runtime/hash_test.go
> +++ b/src/pkg/runtime/hash_test.go
> @@ -397,10 +397,10 @@
>         // all sums inside those bounds with 99% probability.
>         N := n * hashSize
>         var c float64
> -       // find c such that Prob(mean-c*stddev < x < mean+c*stddev)^N > .99
> -       for c = 0.0; math.Pow(math.Erf(c/math.Sqrt(2)), float64(N)) <
> .99; c += .1 {
> +       // find c such that Prob(mean-c*stddev < x < mean+c*stddev)^N >
> .9999
> +       for c = 0.0; math.Pow(math.Erf(c/math.Sqrt(2)), float64(N)) <
> .9999; c += .1 {
>         }
> -       c *= 2.0 // allowed slack - we don't need to be perfectly random
> +       c *= 4.0 // allowed slack - we don't need to be perfectly random
>         mean := .5 * REP
>         stddev := .5 * math.Sqrt(REP)
>         low := int(mean - c*stddev)
>
>
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[khr, 2014-05-09 22:51:00]

*** Submitted as https://code.google.com/p/go/source/detail?r=e30470f3d958 ***

runtime: be a lot more lenient on smhasher avalanche test.

Fixes issue 7943

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/98170043