From: Wil Mahan <wmahan@users.mediawiki.org>
Date: Mon, 11 Oct 2004 17:34:39 +0000 (+0000)
Subject: Bug 589: make random selection slightly more random. PHP's
X-Git-Tag: 1.5.0alpha1~1591
X-Git-Url: https://git.cyclocoop.org/%7B%24admin_url%7Dmembres/modifier.php?a=commitdiff_plain;h=2a03980093b5168a834bbf65e820c5400e29b21b;p=lhc%2Fweb%2Fwiklou.git

Bug 589: make random selection slightly more random. PHP's
mt_rand() function has a maximum value of 2^31-1, which
is small enough that duplicate values can occur due to the
Birthday paradox, e.g. on the English Wikipedia. To fix
this, add a wfRandom() function that calls mt_rand()
twice to get the desired amount of randomness.
---

diff --git a/includes/GlobalFunctions.php b/includes/GlobalFunctions.php
index 971e671db9..276a863134 100644
--- a/includes/GlobalFunctions.php
+++ b/includes/GlobalFunctions.php
@@ -124,6 +124,22 @@ function wfSeedRandom() {
 	}
 }
 
+/**
+ * Get a random decimal value between 0 and 1, in a way
+ * not likely to give duplicate values for any realistic
+ * number of articles.
+ *
+ * @return string
+ */
+function wfRandom() {
+	# The maximum random value is "only" 2^31-1, so get two random
+	# values to reduce the chance of dupes
+	$max = mt_getrandmax();
+	$rand = number_format( mt_rand() * mt_rand()
+		/ $max / $max, 12, '.', '' );
+	return $rand;
+}
+
 /**
  * We want / and : to be included as literal characters in our title URLs.
  * %2F in the page titles seems to fatally break for some reason.
diff --git a/includes/SpecialRandompage.php b/includes/SpecialRandompage.php
index a8c5ed3729..4066c6539c 100644
--- a/includes/SpecialRandompage.php
+++ b/includes/SpecialRandompage.php
@@ -20,10 +20,9 @@ function wfSpecialRandompage() {
 	#
 	# Using a literal constant means the whole thing gets optimized on
 	# the index, and the comparison is both fast and fair.
-	$rand = mt_rand() / mt_getrandmax();
 	
 	# interpolation and sprintf() can muck up with locale-specific decimal separator
-	$randstr = number_format( $rand, 12, ".", "" );
+	$randstr = wfRandom();
 	
 	$db =& wfGetDB( DB_SLAVE );
 	$use_index = $db->useIndexClause( 'cur_random' );
diff --git a/includes/SpecialUndelete.php b/includes/SpecialUndelete.php
index 3e4e2d92af..02527604d8 100644
--- a/includes/SpecialUndelete.php
+++ b/includes/SpecialUndelete.php
@@ -167,7 +167,7 @@ class PageArchive {
 			$redirect = MagicWord::get( MAG_REDIRECT );
 			$redir = $redirect->matchStart( $text ) ? 1 : 0;
 			
-			$rand = number_format( mt_rand() / mt_getrandmax(), 12, '.', '' );
+			$rand = wfRandom();
 			$dbw->insertArray( 'cur', array(
 				'cur_id' => $dbw->nextSequenceValue( 'cur_cur_id_seq' ),
 				'cur_namespace' => $namespace,
diff --git a/includes/Title.php b/includes/Title.php
index 9eb2552a6a..ef1155375d 100644
--- a/includes/Title.php
+++ b/includes/Title.php
@@ -1441,7 +1441,7 @@ class Title {
 		$now = $dbw->timestamp();
 		$won = wfInvertTimestamp( wfTimestamp(TS_MW,$now) );
 		wfSeedRandom();
-		$rand = number_format( mt_rand() / mt_getrandmax(), 12, '.', '' );
+		$rand = wfRandom();
 
 		# Rename cur entry
 		$dbw->updateArray( 'cur',