From: Russ Cox <rsc@golang.org>
Date: Fri, 7 Dec 2012 16:58:44 +0000 (-0500)
Subject: undo CL 6845121 / 79603a5e4cda
X-Git-Tag: go1.1rc2~1695
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=ff2534e076a01445f5852f0fab7a3017ee65c8ba;p=gostls13.git

undo CL 6845121 / 79603a5e4cda

This changes the output of

rand.Seed(0)
perm := rand.Perm(100)

When giving the same seeds to Go 1.0 and Go 1.1 programs
I would like them to generate the same random numbers.

««« original CL description
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://golang.org/cl/6845121

»»»

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6905049
---

diff --git a/src/pkg/math/rand/rand.go b/src/pkg/math/rand/rand.go
index ad2bf2fac0..94f84a85fb 100644
--- a/src/pkg/math/rand/rand.go
+++ b/src/pkg/math/rand/rand.go
@@ -100,7 +100,7 @@ func (r *Rand) Perm(n int) []int {
 	for i := 0; i < n; i++ {
 		m[i] = i
 	}
-	for i := 1; i < n; i++ {
+	for i := 0; i < n; i++ {
 		j := r.Intn(i + 1)
 		m[i], m[j] = m[j], m[i]
 	}