[Webkit-unassigned] [Bug 266869] New: Fix rounding of very large and very small LayoutUnits

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=266869

            Bug ID: 266869
           Summary: Fix rounding of very large and very small LayoutUnits
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ahmad.saleem792 at gmail.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Hi Team,

While looking into LayoutUnit.h code changes in Blink, I noticed that they fixed following bug:

Blink Commit - https://source.chromium.org/chromium/chromium/src/+/a7b04f8fe15406cbf98995da00fc63f73e9fff61

WebKit Source - https://github.com/WebKit/WebKit/blob/008483f2054324eb36aabbd31f58a59ffeff8da8/Source/WebCore/platform/LayoutUnit.h#L159

___

This compiles:

return toInt() + ((fraction().rawValue() + (kFixedPointDenominator / 2)) >> kLayoutUnitFractionalBits);

and

https://github.com/WebKit/WebKit/blob/008483f2054324eb36aabbd31f58a59ffeff8da8/Tools/TestWebKitAPI/Tests/WebCore/LayoutUnitTests.cpp#L84
Test (LayoutUnitRounding):

// The fractional part of LayoutUnit::Max() is 0x3f, so it should round up.
    ASSERT_EQ(((std::numeric_limits<int>::max() / kFixedPointDenominator) + 1), LayoutUnit::max().round());
    // The fractional part of LayoutUnit::Min() is 0, so the next bigger possible
    // value should round down.
    LayoutUnit epsilon;
    epsilon.setRawValue(1);
    ASSERT_EQ(((std::numeric_limits<int>::min() / kFixedPointDenominator)), (LayoutUnit::min() + epsilon).round());
}

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Without change, running above test fails -> run-api-tests WebCoreLayoutUnit.LayoutUnitRounding

Ran 1 tests of 1 with 0 successful
------------------------------
Test suite failed

Failed

    TestWebKitAPI.WebCoreLayoutUnit.LayoutUnitRounding
        /Users/ahmadsaleem/Documents/GitHub-Webkit-Ahmad-Fork/Untitled/Tools/TestWebKitAPI/Tests/WebCore/LayoutUnitTests.cpp:108Expected equality of these values:  ((std::numeric_limits<int>::max() / kFixedPointDenominator) + 1)    Which is: 33554432  LayoutUnit::max().round()    Which is: 33554431

___

Hence, I am raising so we can fix it.

Thanks!

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