[css-values] Rounding of <integer> type should round half towards pos…

…itive infinity

https://bugs.webkit.org/show_bug.cgi?id=260777
rdar://114532926

Reviewed by Darin Adler.

https://drafts.csswg.org/css-values-4/#integers
Rounding to the nearest integer requires rounding in the direction of +∞ when the fractional portion is exactly 0.5.

-1.5 should round to -1, not -2.

* LayoutTests/imported/w3c/web-platform-tests/css/css-values/calc-z-index-fractions-001-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/css/css-values/calc-z-index-fractions-001.html:
* Source/WebCore/css/parser/CSSPropertyParserHelpers.cpp:
(WebCore::CSSPropertyParserHelpers::IntegerTypeRawKnownTokenTypeFunctionConsumer::consume):

Canonical link: https://commits.webkit.org/267339@main

LayoutTests/imported/w3c/web-platform-tests/css/css-values/calc-z-index-fractions-001-expected.txt

@@ -1,4 +1,8 @@
 
+PASS testing z-index: calc(2.5 / 2)
 PASS testing z-index: calc(3 / 2)
-FAIL testing z-index: calc(-3 / 2) assert_equals: expected "-1" but got "-2"
+PASS testing z-index: calc(3.5 / 2)
+PASS testing z-index: calc(-2.5 / 2)
+PASS testing z-index: calc(-3 / 2)
+PASS testing z-index: calc(-3.5 / 2)
 

LayoutTests/imported/w3c/web-platform-tests/css/css-values/calc-z-index-fractions-001.html

@@ -46,11 +46,12 @@
     }
 
  /* verifyComputedStyle(property_name, initial_value, specified_value, expected_value, description) */
-
+    verifyComputedStyle("z-index", "auto", "calc(2.5 / 2)", "1", "testing z-index: calc(2.5 / 2)");
     verifyComputedStyle("z-index", "auto", "calc(3 / 2)", "2", "testing z-index: calc(3 / 2)");
-
+    verifyComputedStyle("z-index", "auto", "calc(3.5 / 2)", "2", "testing z-index: calc(3.5 / 2)");
+    verifyComputedStyle("z-index", "auto", "calc(-2.5 / 2)", "-1", "testing z-index: calc(-2.5 / 2)");
     verifyComputedStyle("z-index", "auto", "calc(-3 / 2)", "-1", "testing z-index: calc(-3 / 2)");
-
+    verifyComputedStyle("z-index", "auto", "calc(-3.5 / 2)", "-2", "testing z-index: calc(-3.5 / 2)");
   }
 
   startTesting();

Source/WebCore/css/parser/CSSPropertyParserHelpers.cpp

@@ -266,7 +266,9 @@ struct IntegerTypeRawKnownTokenTypeFunctionConsumer {
         auto rangeCopy = range;
         if (auto value = consumeCalcRawWithKnownTokenTypeFunction(rangeCopy, CalculationCategory::Number, { }, ValueRange::All)) {
             range = rangeCopy;
-            return clampTo<IntType>(std::round(std::max(value->doubleValue(), computeMinimumValue(integerRange))));
+            // https://drafts.csswg.org/css-values-4/#integers
+            // Rounding to the nearest integer requires rounding in the direction of +∞ when the fractional portion is exactly 0.5.
+            return clampTo<IntType>(std::floor(std::max(value->doubleValue(), computeMinimumValue(integerRange)) + 0.5));
         }
 
         return std::nullopt;