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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/201053">201053</a></dd>
<dt>Author</dt> <dd>commit-queue@webkit.org</dd>
<dt>Date</dt> <dd>2016-05-17 15:52:47 -0700 (Tue, 17 May 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>REGRESSION(<a href="http://trac.webkit.org/projects/webkit/changeset/192855">r192855</a>): Math.random() always produces the same first 7 decimal points the first two invocations
https://bugs.webkit.org/show_bug.cgi?id=157805
<rdar://problem/26327851>
Patch by Joseph Pecoraro <pecoraro@apple.com> on 2016-05-17
Reviewed by Geoffrey Garen.
Source/WTF:
* wtf/WeakRandom.h:
(WTF::WeakRandom::setSeed):
Advance once to randomize the 32bit seed across the 128bit state
and avoid re-using 64bits of state in the second advance.
LayoutTests:
* js/dom/math-random-initial-values-expected.txt: Added.
* js/dom/math-random-initial-values.html: Added.
* js/resources/math-random-initial-values-iframe.html: Added.
Test that less then 5% of the time, early Math.random invocations
produce very similiar values. Before this change we were failing
100%, but after we see similiar values mostly around 0-3%.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsChangeLog">trunk/LayoutTests/ChangeLog</a></li>
<li><a href="#trunkSourceWTFChangeLog">trunk/Source/WTF/ChangeLog</a></li>
<li><a href="#trunkSourceWTFwtfWeakRandomh">trunk/Source/WTF/wtf/WeakRandom.h</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsjsdommathrandominitialvaluesexpectedtxt">trunk/LayoutTests/js/dom/math-random-initial-values-expected.txt</a></li>
<li><a href="#trunkLayoutTestsjsdommathrandominitialvalueshtml">trunk/LayoutTests/js/dom/math-random-initial-values.html</a></li>
<li><a href="#trunkLayoutTestsjsresourcesmathrandominitialvaluesiframehtml">trunk/LayoutTests/js/resources/math-random-initial-values-iframe.html</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkLayoutTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/ChangeLog (201052 => 201053)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/ChangeLog 2016-05-17 22:39:00 UTC (rev 201052)
+++ trunk/LayoutTests/ChangeLog 2016-05-17 22:52:47 UTC (rev 201053)
</span><span class="lines">@@ -1,3 +1,18 @@
</span><ins>+2016-05-17 Joseph Pecoraro <pecoraro@apple.com>
+
+ REGRESSION(r192855): Math.random() always produces the same first 7 decimal points the first two invocations
+ https://bugs.webkit.org/show_bug.cgi?id=157805
+ <rdar://problem/26327851>
+
+ Reviewed by Geoffrey Garen.
+
+ * js/dom/math-random-initial-values-expected.txt: Added.
+ * js/dom/math-random-initial-values.html: Added.
+ * js/resources/math-random-initial-values-iframe.html: Added.
+ Test that less then 5% of the time, early Math.random invocations
+ produce very similiar values. Before this change we were failing
+ 100%, but after we see similiar values mostly around 0-3%.
+
</ins><span class="cx"> 2016-05-17 Keith Miller <keith_miller@apple.com>
</span><span class="cx">
</span><span class="cx"> Rollout r200426 since it causes PLT regressions.
</span></span></pre></div>
<a id="trunkLayoutTestsjsdommathrandominitialvaluesexpectedtxt"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/js/dom/math-random-initial-values-expected.txt (0 => 201053)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/js/dom/math-random-initial-values-expected.txt (rev 0)
+++ trunk/LayoutTests/js/dom/math-random-initial-values-expected.txt 2016-05-17 22:52:47 UTC (rev 201053)
</span><span class="lines">@@ -0,0 +1,10 @@
</span><ins>+This tests early Math.random values are not consistently nearly identical.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS framesWithSimiliarEarlyRandomValues <= 5 is true
+PASS successfullyParsed is true
+
+TEST COMPLETE
+
</ins></span></pre></div>
<a id="trunkLayoutTestsjsdommathrandominitialvalueshtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/js/dom/math-random-initial-values.html (0 => 201053)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/js/dom/math-random-initial-values.html (rev 0)
+++ trunk/LayoutTests/js/dom/math-random-initial-values.html 2016-05-17 22:52:47 UTC (rev 201053)
</span><span class="lines">@@ -0,0 +1,44 @@
</span><ins>+<!DOCTYPE HTML>
+<html>
+<head>
+<script src="../../resources/js-test-pre.js"></script>
+</head>
+<body>
+<script>
+window.jsTestIsAsync = true;
+
+description("This tests early Math.random values are not consistently nearly identical.");
+
+var seen = 0;
+var expected = 100;
+var framesWithSimiliarEarlyRandomValues = 0;
+var lastRandom1 = 0;
+
+window.addEventListener("message", function(event) {
+ if (event.data.similiar)
+ framesWithSimiliarEarlyRandomValues++;
+
+ if (event.data.random1 === lastRandom1)
+ testFailed("Random number should be different between frames");
+ lastRandom1 = event.data.random1;
+
+ if (++seen === expected) {
+ shouldBeTrue("framesWithSimiliarEarlyRandomValues <= 5");
+ if (framesWithSimiliarEarlyRandomValues > 5)
+ debug("framesWithSimiliarEarlyRandomValues: " + framesWithSimiliarEarlyRandomValues);
+ finishJSTest();
+ }
+});
+
+function createFrame() {
+ var iframe = document.createElement("iframe");
+ iframe.src = "../resources/math-random-initial-values-iframe.html";
+ document.body.appendChild(iframe);
+}
+
+for (var i = 0; i < expected; ++i)
+ createFrame();
+</script>
+<script src="../../resources/js-test-post.js"></script>
+</body>
+</html>
</ins></span></pre></div>
<a id="trunkLayoutTestsjsresourcesmathrandominitialvaluesiframehtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/js/resources/math-random-initial-values-iframe.html (0 => 201053)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/js/resources/math-random-initial-values-iframe.html (rev 0)
+++ trunk/LayoutTests/js/resources/math-random-initial-values-iframe.html 2016-05-17 22:52:47 UTC (rev 201053)
</span><span class="lines">@@ -0,0 +1,6 @@
</span><ins>+<script>
+var random1 = Math.random();
+var random2 = Math.random();
+var similiar = Math.floor(random1 * 1000) === Math.floor(random2 * 1000);
+window.top.postMessage({similiar, random1, random2}, "*");
+</script>
</ins></span></pre></div>
<a id="trunkSourceWTFChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/ChangeLog (201052 => 201053)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/ChangeLog 2016-05-17 22:39:00 UTC (rev 201052)
+++ trunk/Source/WTF/ChangeLog 2016-05-17 22:52:47 UTC (rev 201053)
</span><span class="lines">@@ -1,3 +1,16 @@
</span><ins>+2016-05-17 Joseph Pecoraro <pecoraro@apple.com>
+
+ REGRESSION(r192855): Math.random() always produces the same first 7 decimal points the first two invocations
+ https://bugs.webkit.org/show_bug.cgi?id=157805
+ <rdar://problem/26327851>
+
+ Reviewed by Geoffrey Garen.
+
+ * wtf/WeakRandom.h:
+ (WTF::WeakRandom::setSeed):
+ Advance once to randomize the 32bit seed across the 128bit state
+ and avoid re-using 64bits of state in the second advance.
+
</ins><span class="cx"> 2016-05-17 Dean Jackson <dino@apple.com>
</span><span class="cx">
</span><span class="cx"> Remove ES6_GENERATORS flag
</span></span></pre></div>
<a id="trunkSourceWTFwtfWeakRandomh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/WeakRandom.h (201052 => 201053)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/WeakRandom.h 2016-05-17 22:39:00 UTC (rev 201052)
+++ trunk/Source/WTF/wtf/WeakRandom.h 2016-05-17 22:52:47 UTC (rev 201053)
</span><span class="lines">@@ -56,6 +56,7 @@
</span><span class="cx">
</span><span class="cx"> m_low = seed;
</span><span class="cx"> m_high = seed;
</span><ins>+ advance();
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> unsigned seed() const { return m_seed; }
</span></span></pre>
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