Changeset 280632 in webkit

Timestamp:

Aug 4, 2021, 5:57:03 AM (5 years ago)

Author:

Martin Robinson

Message:

Add a HashTraits implementation for LayoutUnit
​https://bugs.webkit.org/show_bug.cgi?id=228630

Reviewed by Fujii Hironori.

No new tests. This should not change behavior in an easily-observable way, but
could prevent rare hashing problems in the future.

• page/scrolling/ScrollSnapOffsetsInfo.cpp:

(WebCore::updateSnapOffsetsForScrollableArea): Use LayoutUnit as the hash, which avoids
and extra conversion to float.

• platform/LayoutUnit.h: Add a HashTraits implementation for LayoutUnit.

Location:

trunk/Source/WebCore

Files:

• ChangeLog (modified) (1 diff)
• page/scrolling/ScrollSnapOffsetsInfo.cpp (modified) (2 diffs)
• platform/LayoutUnit.h (modified) (2 diffs)

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2021-08-04  Martin Robinson  <mrobinson@webkit.org>
+
+        Add a HashTraits implementation for LayoutUnit
+        https://bugs.webkit.org/show_bug.cgi?id=228630
+
+        Reviewed by Fujii Hironori.
+
+        No new tests. This should not change behavior in an easily-observable way, but
+        could prevent rare hashing problems in the future.
+
+        * page/scrolling/ScrollSnapOffsetsInfo.cpp:
+        (WebCore::updateSnapOffsetsForScrollableArea): Use LayoutUnit as the hash, which avoids
+        and extra conversion to float.
+        * platform/LayoutUnit.h: Add a HashTraits implementation for LayoutUnit.
+
 2021-08-04  Cathie Chen  <cathiechen@igalia.com>
 

trunk/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp

@@ -230 +230 @@
     }
 
-    auto addOrUpdateStopForSnapOffset = [](HashMap<float, SnapOffset<LayoutUnit>>& offsets, LayoutUnit newOffset, ScrollSnapStop stop, bool hasSnapAreaLargerThanViewport, size_t snapAreaIndices)
+    auto addOrUpdateStopForSnapOffset = [](HashMap<LayoutUnit, SnapOffset<LayoutUnit>>& offsets, LayoutUnit newOffset, ScrollSnapStop stop, bool hasSnapAreaLargerThanViewport, size_t snapAreaIndices)
     {
         auto offset = offsets.ensure(newOffset, [&] {
@@ -244 +244 @@
     };
 
-    HashMap<float, SnapOffset<LayoutUnit>> verticalSnapOffsetsMap;
-    HashMap<float, SnapOffset<LayoutUnit>> horizontalSnapOffsetsMap;
+    HashMap<LayoutUnit, SnapOffset<LayoutUnit>> verticalSnapOffsetsMap;
+    HashMap<LayoutUnit, SnapOffset<LayoutUnit>> horizontalSnapOffsetsMap;
     Vector<LayoutRect> snapAreas;
 

trunk/Source/WebCore/platform/LayoutUnit.h

@@ -35 +35 @@
 #include <math.h>
 #include <stdlib.h>
+#include <wtf/HashTraits.h>
 #include <wtf/MathExtras.h>
 #include <wtf/SaturatedArithmetic.h>
@@ -839 +840 @@
 
 } // namespace WebCore
+
+namespace WTF {
+
+template<> struct DefaultHash<WebCore::LayoutUnit> {
+    static unsigned hash(const WebCore::LayoutUnit& p) { return DefaultHash<int>::hash(p.rawValue()); }
+    static bool equal(const WebCore::LayoutUnit& a, const WebCore::LayoutUnit& b) { return a == b; }
+    static const bool safeToCompareToEmptyOrDeleted = true;
+};
+
+// The empty value is INT_MIN, the deleted value is INT_MAX. During the course of layout
+// these values are typically only used to represent uninitialized values, so they are
+// good candidates to represent the deleted and empty values in HashMaps as well.
+template<> struct HashTraits<WebCore::LayoutUnit> : GenericHashTraits<WebCore::LayoutUnit> {
+    static constexpr bool emptyValueIsZero = false;
+    static WebCore::LayoutUnit emptyValue()
+    {
+        WebCore::LayoutUnit value;
+        value.setRawValue(std::numeric_limits<int>::min());
+        return value;
+    }
+    static void constructDeletedValue(WebCore::LayoutUnit& slot) { slot.setRawValue(std::numeric_limits<int>::max()); }
+    static bool isDeletedValue(WebCore::LayoutUnit value) { return value.rawValue() == std::numeric_limits<int>::max(); }
+};
+
+} // namespace WTF