code review 6845121: math/rand: remove noop iteration in Perm

math/rand: remove noop iteration in Perm

The first iteration always do `m[0], m[0] = m[0], m[0]`, because
`rand.Intn(1)` is 0.

fun note: IIRC in TAOCP version of this algorithm, `i` goes
backward (n-1->1), meaning that the "already" shuffled part of the
array is never altered betweens iterations, while in the current
implementation the "not-yet" shuffled part of the array is
conserved between iterations.

[proppy, 2012-12-01 09:29:17]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
http://code.google.com/p/go

[bradfitz, 2012-12-01 22:11:59]

*** Submitted as https://code.google.com/p/go/source/detail?r=79603a5e4cda ***

math/rand: remove noop iteration in Perm

The first iteration always do `m[0], m[0] = m[0], m[0]`, because
`rand.Intn(1)` is 0.

fun note: IIRC in TAOCP version of this algorithm, `i` goes
backward (n-1->1), meaning that the "already" shuffled part of the
array is never altered betweens iterations, while in the current
implementation the "not-yet" shuffled part of the array is
conserved between iterations.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/6845121

Committer: Brad Fitzpatrick <bradfitz@golang.org>

[rsc, 2012-12-07 14:37:01]

This changes the output generated by the random number generator
with a given seed. While we have never promised that won't change,
I would like to avoid changing it unnecessarily, so I am going to undo
this CL.

[bradfitz, 2012-12-07 14:44:28]

Add a test too, then?
 On Dec 7, 2012 9:37 AM, <rsc@golang.org> wrote:

> This changes the output generated by the random number generator
> with a given seed. While we have never promised that won't change,
> I would like to avoid changing it unnecessarily, so I am going to undo
> this CL.
>
>
>
https://codereview.appspot.**com/6845121/<https://codereview.appspot.com/6845...
>

[rsc, 2012-12-07 15:13:25]

Rollback and test sent, separately. 6905049 and 6907048