Title: [138041] trunk/Source/WebCore
- Revision
- 138041
- Author
- e...@chromium.org
- Date
- 2012-12-18 10:46:10 -0800 (Tue, 18 Dec 2012)
Log Message
Optimize LayoutUnit::boundedMultiply
https://bugs.webkit.org/show_bug.cgi?id=105216
Reviewed by Levi Weintraub.
LayoutUnit::boundedMultiply is used for multiplication that's
prone to overflow and for all LayoutUnit multiplication if
SATURATED_LAYOUT_ARITHMETIC is enabled. The current approach is
quite inefficient.
Change it to use a more efficient saturated multiplication
implementation. As the implementation needs to use
kFixedPointDenominator it is implemented in LayoutUnit.h instead
of in wtf/SaturatedArithmetic.h.
Test: Covered by TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp
* platform/LayoutUnit.h:
(WebCore::boundedMultiply):
Modified Paths
Diff
Modified: trunk/Source/WebCore/ChangeLog (138040 => 138041)
--- trunk/Source/WebCore/ChangeLog 2012-12-18 18:43:38 UTC (rev 138040)
+++ trunk/Source/WebCore/ChangeLog 2012-12-18 18:46:10 UTC (rev 138041)
@@ -1,3 +1,25 @@
+2012-12-17 Emil A Eklund <e...@chromium.org>
+
+ Optimize LayoutUnit::boundedMultiply
+ https://bugs.webkit.org/show_bug.cgi?id=105216
+
+ Reviewed by Levi Weintraub.
+
+ LayoutUnit::boundedMultiply is used for multiplication that's
+ prone to overflow and for all LayoutUnit multiplication if
+ SATURATED_LAYOUT_ARITHMETIC is enabled. The current approach is
+ quite inefficient.
+
+ Change it to use a more efficient saturated multiplication
+ implementation. As the implementation needs to use
+ kFixedPointDenominator it is implemented in LayoutUnit.h instead
+ of in wtf/SaturatedArithmetic.h.
+
+ Test: Covered by TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp
+
+ * platform/LayoutUnit.h:
+ (WebCore::boundedMultiply):
+
2012-12-18 Bear Travis <betra...@adobe.com>
[CSS Exclusions] Blocks should not re-use their parent's ExclusionShapeInsideInfo
Modified: trunk/Source/WebCore/platform/LayoutUnit.h (138040 => 138041)
--- trunk/Source/WebCore/platform/LayoutUnit.h 2012-12-18 18:43:38 UTC (rev 138040)
+++ trunk/Source/WebCore/platform/LayoutUnit.h 2012-12-18 18:46:10 UTC (rev 138041)
@@ -483,15 +483,19 @@
inline LayoutUnit boundedMultiply(const LayoutUnit& a, const LayoutUnit& b)
{
#if ENABLE(SUBPIXEL_LAYOUT)
+ int64_t result = static_cast<int64_t>(a.rawValue()) * static_cast<int64_t>(b.rawValue()) / kEffectiveFixedPointDenominator;
+ int32_t high = result >> 32;
+ int32_t low = result;
+ uint32_t saturated = (static_cast<uint32_t>(a.rawValue() ^ b.rawValue()) >> 31) + std::numeric_limits<int>::max();
+ // If the higher 32 bits does not match the lower 32 with sign extension the operation overflowed.
+ if (high != low >> 31)
+ result = saturated;
+
LayoutUnit returnVal;
- long long rawVal = static_cast<long long>(a.rawValue()) * b.rawValue() / kEffectiveFixedPointDenominator;
- if (rawVal > std::numeric_limits<int>::max())
- return LayoutUnit::max();
- if (rawVal < std::numeric_limits<int>::min())
- return LayoutUnit::min();
- returnVal.setRawValue(rawVal);
+ returnVal.setRawValue(static_cast<int>(result));
return returnVal;
#else
+ // FIXME: Should be bounded even in the non-subpixel case.
return a.rawValue() * b.rawValue();
#endif
}
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