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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/145759">145759</a></dd>
<dt>Author</dt> <dd>oliver@apple.com</dd>
<dt>Date</dt> <dd>2013-03-13 14:51:07 -0700 (Wed, 13 Mar 2013)</dd>
</dl>

<h3>Log Message</h3>
<pre>Simplify Checked&lt;&gt; multiplication
https://bugs.webkit.org/show_bug.cgi?id=112286

Reviewed by James Robinson.

Source/WTF:

Trying to correctly identify multiplication by zero complicated the
unsigned * unsigned multiply, and still didn't handle all cases correctly.
Now we just do the normal division based approach to overflow detection
leading to much simpler reasoning.

Would be nice if we could have a jo style intrinsic one day.

* wtf/CheckedArithmetic.h:

Tools:

Add tests for multiplication by zero and max to ensure we don't
mess them up should we ever make changes to Checked&lt;&gt; in future.

* TestWebKitAPI/Tests/WTF/CheckedArithmeticOperations.cpp:
(TestWebKitAPI):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWTFChangeLog">trunk/Source/WTF/ChangeLog</a></li>
<li><a href="#trunkSourceWTFwtfCheckedArithmetich">trunk/Source/WTF/wtf/CheckedArithmetic.h</a></li>
<li><a href="#trunkToolsChangeLog">trunk/Tools/ChangeLog</a></li>
<li><a href="#trunkToolsTestWebKitAPITestsWTFCheckedArithmeticOperationscpp">trunk/Tools/TestWebKitAPI/Tests/WTF/CheckedArithmeticOperations.cpp</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWTFChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/ChangeLog (145758 => 145759)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/ChangeLog        2013-03-13 21:50:11 UTC (rev 145758)
+++ trunk/Source/WTF/ChangeLog        2013-03-13 21:51:07 UTC (rev 145759)
</span><span class="lines">@@ -1,3 +1,19 @@
</span><ins>+2013-03-13  Oliver Hunt  &lt;oliver@apple.com&gt;
+
+        Simplify Checked&lt;&gt; multiplication
+        https://bugs.webkit.org/show_bug.cgi?id=112286
+
+        Reviewed by James Robinson.
+
+        Trying to correctly identify multiplication by zero complicated the
+        unsigned * unsigned multiply, and still didn't handle all cases correctly.
+        Now we just do the normal division based approach to overflow detection
+        leading to much simpler reasoning.
+
+        Would be nice if we could have a jo style intrinsic one day.
+
+        * wtf/CheckedArithmetic.h:
+
</ins><span class="cx"> 2013-03-13  Dean Jackson  &lt;dino@apple.com&gt;
</span><span class="cx"> 
</span><span class="cx">         Unreviewed attempted build fix for Windows. SchedulePair.cpp -&gt; SchedulePairCF.cpp
</span></span></pre></div>
<a id="trunkSourceWTFwtfCheckedArithmetich"></a>
<div class="modfile"><h4>Modified: trunk/Source/WTF/wtf/CheckedArithmetic.h (145758 => 145759)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WTF/wtf/CheckedArithmetic.h        2013-03-13 21:50:11 UTC (rev 145758)
+++ trunk/Source/WTF/wtf/CheckedArithmetic.h        2013-03-13 21:51:07 UTC (rev 145759)
</span><span class="lines">@@ -321,10 +321,13 @@
</span><span class="cx"> 
</span><span class="cx">     static inline bool multiply(LHS lhs, RHS rhs, ResultType&amp; result) WARN_UNUSED_RETURN
</span><span class="cx">     {
</span><del>-        ResultType temp = lhs * rhs;
-        if (temp &lt; lhs)
-            return !rhs;
-        result = temp;
</del><ins>+        if (!lhs || !rhs) {
+            result = 0;
+            return true;
+        }
+        if (std::numeric_limits&lt;ResultType&gt;::max() / lhs &lt; rhs)
+            return false;
+        result = lhs * rhs;
</ins><span class="cx">         return true;
</span><span class="cx">     }
</span><span class="cx"> 
</span></span></pre></div>
<a id="trunkToolsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Tools/ChangeLog (145758 => 145759)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Tools/ChangeLog        2013-03-13 21:50:11 UTC (rev 145758)
+++ trunk/Tools/ChangeLog        2013-03-13 21:51:07 UTC (rev 145759)
</span><span class="lines">@@ -1,3 +1,16 @@
</span><ins>+2013-03-13  Oliver Hunt  &lt;oliver@apple.com&gt;
+
+        Simplify Checked&lt;&gt; multiplication
+        https://bugs.webkit.org/show_bug.cgi?id=112286
+
+        Reviewed by James Robinson.
+
+        Add tests for multiplication by zero and max to ensure we don't
+        mess them up should we ever make changes to Checked&lt;&gt; in future.
+
+        * TestWebKitAPI/Tests/WTF/CheckedArithmeticOperations.cpp:
+        (TestWebKitAPI):
+
</ins><span class="cx"> 2013-03-13  Simon Hausmann  &lt;simon.hausmann@digia.com&gt;
</span><span class="cx"> 
</span><span class="cx">         [Qt] Unreviewed prospective Windows build fix
</span></span></pre></div>
<a id="trunkToolsTestWebKitAPITestsWTFCheckedArithmeticOperationscpp"></a>
<div class="modfile"><h4>Modified: trunk/Tools/TestWebKitAPI/Tests/WTF/CheckedArithmeticOperations.cpp (145758 => 145759)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Tools/TestWebKitAPI/Tests/WTF/CheckedArithmeticOperations.cpp        2013-03-13 21:50:11 UTC (rev 145758)
+++ trunk/Tools/TestWebKitAPI/Tests/WTF/CheckedArithmeticOperations.cpp        2013-03-13 21:51:07 UTC (rev 145759)
</span><span class="lines">@@ -70,6 +70,41 @@
</span><span class="cx">         EXPECT_EQ(true, (value += coerceLiteral(1)).hasOverflowed()); \
</span><span class="cx">         EXPECT_EQ(true, value.hasOverflowed()); \
</span><span class="cx">         value = 10; \
</span><ins>+        type _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (value * Checked&lt;type, RecordOverflow&gt;(0)).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (Checked&lt;type, RecordOverflow&gt;(0) * value).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidOverflow == (value * Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max())).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidOverflow == (Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max()) * value).safeGet(_value)); \
+        value = 0; \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (value * Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max())).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max()) * value).safeGet(_value)); \
+        value = 1; \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (value * Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max())).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max()) * value).safeGet(_value)); \
+        _value = 0; \
+        value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (value * Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max())).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max()) * (type)0).safeGet(_value)); \
+        _value = 0; \
+        value = 1; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (value * Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max())).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidNotOverflow == (Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max()) * (type)1).safeGet(_value)); \
+        _value = 0; \
+        value = 2; \
+        EXPECT_EQ(true, CheckedState::DidOverflow == (value * Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max())).safeGet(_value)); \
+        _value = 0; \
+        EXPECT_EQ(true, CheckedState::DidOverflow == (Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max()) * (type)2).safeGet(_value)); \
+        value = 10; \
+        EXPECT_EQ(true, (value * Checked&lt;type, RecordOverflow&gt;(std::numeric_limits&lt;type&gt;::max())).hasOverflowed()); \
</ins><span class="cx">         MixedSignednessTest(EXPECT_EQ(coerceLiteral(0), (value + -10).unsafeGet())); \
</span><span class="cx">         MixedSignednessTest(EXPECT_EQ(0U, (value - 10U).unsafeGet())); \
</span><span class="cx">         MixedSignednessTest(EXPECT_EQ(coerceLiteral(0), (-10 + value).unsafeGet())); \
</span></span></pre>
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