From 1d7bf6accb64a1ee9a75cf9889d941a713d2d5c2 Mon Sep 17 00:00:00 2001
From: CyrilFerlicot <cyril@ferlicot.me>
Date: Fri, 17 Feb 2023 15:52:10 +0100
Subject: [PATCH] Speed up random permutations + allow to set ourself the
 random generator

"Before"
[PMPermutation randomPermutation: 30000] timeToRun. "0:00:00:05.666"

"After"
[PMPermutation randomPermutation: 30000] timeToRun. "0:00:00:00.006"
---
 src/Math-Permutation/PMPermutation.class.st   | 43 +++++++++++--------
 .../PMPermutationTest.class.st                | 20 ++++-----
 2 files changed, 36 insertions(+), 27 deletions(-)

diff --git a/src/Math-Permutation/PMPermutation.class.st b/src/Math-Permutation/PMPermutation.class.st
index 57c1e3510..363755096 100644
--- a/src/Math-Permutation/PMPermutation.class.st
+++ b/src/Math-Permutation/PMPermutation.class.st
@@ -57,20 +57,20 @@ PMPermutation class >> fromCycles: aCollectionofCollections [
 ]
 
 { #category : #accessing }
-PMPermutation class >> generator:arrayOfPermutations [
-|f max generators|
-max:=(arrayOfPermutations collect:[:g|g size])max.
-generators:=arrayOfPermutations collect:[:g| g extendTo: max].
-f:=PMFixpoint 
-  block: [ :s| |aSet|
-				aSet:=Set newFrom: s.
-				s do:[:p|s do:[:q|
-						aSet add:(p permute:q)]].
-				aSet]
-  value: generators.
-f verbose:false.
-^f evaluate asArray.
+PMPermutation class >> generator: arrayOfPermutations [
 
+	| f max generators |
+	max := (arrayOfPermutations collect: [ :g | g size ]) max.
+	generators := arrayOfPermutations collect: [ :g | g extendTo: max ].
+	f := PMFixpoint
+		     block: [ :s |
+			     | aSet |
+			     aSet := Set newFrom: s.
+			     s do: [ :p | s do: [ :q | aSet add: (p permute: q) ] ].
+			     aSet ]
+		     value: generators.
+	f verbose: false.
+	^ f evaluate asArray
 ]
 
 { #category : #'instance creation' }
@@ -87,19 +87,28 @@ uses super withAll: since this way a primitive can be used, which is generally m
 
 { #category : #'instance creation' }
 PMPermutation class >> ordering: aCollection [
-"use #newFrom: for an unreduced Permutation! but then most things won't work before you call #reduce.
+	"use #newFrom: for an unreduced Permutation! but then most things won't work before you call #reduce.
 aCollection must consist of elements that can be sorted via #<="
-^( super withAll:  aCollection ) reduce
+
+	^ (super withAll: aCollection) reduce
 ]
 
 { #category : #accessing }
 PMPermutation class >> randomGenerator [
-^RandomGenerator ifNil: [ RandomGenerator := Random new ]
+
+	^ RandomGenerator ifNil: [ RandomGenerator := Random new ]
+]
+
+{ #category : #accessing }
+PMPermutation class >> randomGenerator: aGenerator [
+
+	^ RandomGenerator := aGenerator
 ]
 
 { #category : #'instance creation' }
 PMPermutation class >> randomPermutation: size [
-^self ordering: (self randomGenerator next:size)
+
+	^ self newFrom: ((1 to: size) asArray shuffleBy: self randomGenerator)
 ]
 
 { #category : #'instance creation' }
diff --git a/src/Math-Tests-Permutation/PMPermutationTest.class.st b/src/Math-Tests-Permutation/PMPermutationTest.class.st
index 2e54a1890..94cd36b00 100644
--- a/src/Math-Tests-Permutation/PMPermutationTest.class.st
+++ b/src/Math-Tests-Permutation/PMPermutationTest.class.st
@@ -236,17 +236,17 @@ self assert: g third isFloat.
 
 { #category : #'class tests' }
 PMPermutationTest >> testRandomPermutation [
-|p p2 l|
-l:=173."relatively high for a randomized test"
-PMPermutation randomGenerator seed:10. "can be put into comments for a randomized test"
-p:=PMPermutation randomPermutation: l.
-p2:=PMPermutation randomPermutation: l.
-self deny: p=p2.
-self assert: p class equals: PMPermutation.
-l:=1 to: l.
-self assert: p sorted equals: l.
-self assert: p2 sorted equals: l.
 
+	| p p2 l |
+	l := 173. "relatively high for a randomized test"
+	PMPermutation randomGenerator seed: 10. "can be put into comments for a randomized test"
+	p := PMPermutation randomPermutation: l.
+	p2 := PMPermutation randomPermutation: l.
+	self deny: p equals: p2.
+	self assert: p class equals: PMPermutation.
+	l := 1 to: l.
+	self assert: p sorted equals: l.
+	self assert: p2 sorted equals: l
 ]
 
 { #category : #tests }