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undo CL 6845121 / 79603a5e4cda

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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
This commit is contained in:
Russ Cox 2012-12-07 11:58:44 -05:00 committed by Brad Fitzpatrick
parent 9088d17afb
commit ff2534e076
1 changed files with 1 additions and 1 deletions
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2
src/pkg/math/rand/rand.go
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@ -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]
}