From: Nuria Ruiz <nuria@wikimedia.org>
Date: Thu, 23 Aug 2018 23:07:33 +0000 (-0700)
Subject: mediawiki.user: Small perf tweak for generateRandomSessionId
X-Git-Tag: 1.34.0-rc.0~4309^2
X-Git-Url: http://git.cyclocoop.org/%7B%24www_url%7Dadmin/compta/operations/?a=commitdiff_plain;h=54a976d507aeaf618ab4ebb0d7e6a6a3ba2ea604;p=lhc%2Fweb%2Fwiklou.git

mediawiki.user: Small perf tweak for generateRandomSessionId

Consolidate loop + join into explicit string concatenation

Bug: T201124
Change-Id: Ie7c7ddd29783ada142fbb7b726caa697048802f3
---

diff --git a/resources/src/mediawiki.user.js b/resources/src/mediawiki.user.js
index bf23da1809..251b108078 100644
--- a/resources/src/mediawiki.user.js
+++ b/resources/src/mediawiki.user.js
@@ -46,35 +46,31 @@
 		 */
 		generateRandomSessionId: function () {
 			var rnds, i,
-				hexRnds = new Array( 5 ),
 				// Support: IE 11
 				crypto = window.crypto || window.msCrypto;
 
 			if ( crypto && crypto.getRandomValues && typeof Uint16Array === 'function' ) {
-
 				// Fill an array with 5 random values, each of which is 16 bits.
 				// Note that Uint16Array is array-like but does not implement Array.
 				rnds = new Uint16Array( 5 );
 				crypto.getRandomValues( rnds );
-
 			} else {
-
 				// 0x10000 is 2^16 so the operation below will return a number
 				// between 2^16 and zero
 				for ( i = 0; i < 5; i++ ) {
 					rnds[ i ] = Math.floor( Math.random() * 0x10000 );
 				}
 			}
-			// Convert the 5 16bit-numbers into 20 characters (4 hex chars per 16 bits)
-			for ( i = 0; i < 5; i++ ) {
-				// Add 0x1000 before converting to hex and strip the extra character
-				// after converting to keep the leading zeros.
-				hexRnds[ i ] = ( rnds[ i ] + 0x10000 ).toString( 16 ).slice( 1 );
-			}
 
+			// Convert the 5 16bit-numbers into 20 characters (4 hex per 16 bits).
 			// Concatenation of two random integers with entropy n and m
-			// returns a string with entropy n+m if those strings are independent
-			return hexRnds.join( '' );
+			// returns a string with entropy n+m if those strings are independent.
+			// Tested that below code is faster than array + loop + join.
+			return ( rnds[ 0 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+				( rnds[ 1 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+				( rnds[ 2 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+				( rnds[ 3 ] + 0x10000 ).toString( 16 ).slice( 1 ) +
+				( rnds[ 4 ] + 0x10000 ).toString( 16 ).slice( 1 );
 		},
 
 		/**