Attachment 339080 Details for Bug 185115 – Patch

[patch] Patch

bug-185115-20180428163317.patch (text/plain), 3.91 KB, created by corydoras on 2018-04-28 16:33:18 PDT

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Creator: corydoras

Created: 2018-04-28 16:33:18 PDT

Size: 3.91 KB

patch

obsolete

>Subversion Revision: 231131
>diff --git a/Source/JavaScriptCore/ChangeLog b/Source/JavaScriptCore/ChangeLog
>index b3474d05e20bd694553fe621a56875a0a578b3f4..52b1e5b91733e2d7768c9c3793f7bd7ca5f6de2e 100644
>--- a/Source/JavaScriptCore/ChangeLog
>+++ b/Source/JavaScriptCore/ChangeLog
>@@ -1,3 +1,30 @@
>+2018-04-28  Peter Ammon  <corydoras@ridiculousfish.com>
>+
>+        [JSC] Correct Math.round for largest value below 0.5
>+        https://bugs.webkit.org/show_bug.cgi?id=185115
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        Prior to this fix, Math.round would ceil() the input, compute the delta,
>+        and then correct it if the delta exceeded 0.5. However if the input is the
>+        largest representable value below 0.5, the delta suffers precision loss and
>+        is gets rounded down to 0.5 instead of being slightly larger. Therefore
>+        Math.round() of this input would be 1.0 instead of the correct 0.0.
>+
>+        Switch to an implementation (suggested by Stephen Canon) of using floor()
>+        and incrementing if the delta is *at least* 0.5. This corrects the handling
>+        of the before-0.5 input, because the delta becomes equal to the input and
>+        so there is no precision loss.
>+
>+        For the negated input (i.e. nextafter(-0.5, +inf)) we still suffer precision
>+        loss and compute a delta of 0.5, but the >= test means we will still increment
>+        in this case, rounding to 0.
>+
>+        Unfortunately we must do a sign fixup afterwards, because incrementing -1
>+        produces +0.
>+
>+        * runtime/MathCommon.cpp:
>+
> 2018-04-27  Caio Lima  <ticaiolima@gmail.com>
> 
>         [ESNext][BigInt] Implement support for "*" operation
>diff --git a/Source/JavaScriptCore/runtime/MathCommon.cpp b/Source/JavaScriptCore/runtime/MathCommon.cpp
>index bdf1487ec1ee79dab553f353ba515f623c5a959d..c0d7bcc9f293047ae0f90284e44870c383b6fcd4 100644
>--- a/Source/JavaScriptCore/runtime/MathCommon.cpp
>+++ b/Source/JavaScriptCore/runtime/MathCommon.cpp
>@@ -490,8 +490,8 @@ static inline bool isStrictInt32(double value)
> extern "C" {
> double jsRound(double value)
> {
>-    double integer = ceil(value);
>-    return integer - (integer - value > 0.5);
>+    double integer = floor(value);
>+    return copysign(integer + (value - integer >= 0.5), value);
> }
> 
> #if CALLING_CONVENTION_IS_STDCALL || CPU(ARM_THUMB2)
>diff --git a/JSTests/ChangeLog b/JSTests/ChangeLog
>index 1bdb91c71ce44cf7de60a8f7960ae5392fcc3a33..262954c909ad8df05400dbf88b762a767cf8564d 100644
>--- a/JSTests/ChangeLog
>+++ b/JSTests/ChangeLog
>@@ -1,3 +1,14 @@
>+2018-04-28  Peter Ammon  <corydoras@ridiculousfish.com>
>+
>+        [JSC] Correct Math.round for largest value below 0.5
>+        https://bugs.webkit.org/show_bug.cgi?id=185115
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        Math.round() tests for value preceding 0.5
>+
>+        * stress/math-round-basics.js:
>+
> 2018-04-27  Caio Lima  <ticaiolima@gmail.com>
> 
>         [ESNext][BigInt] Implement support for "*" operation
>diff --git a/JSTests/stress/math-round-basics.js b/JSTests/stress/math-round-basics.js
>index f61a6d4f4769585fe5b9f56ff0eabc402302413c..f301eae96946c2e0b856c5d4d4e49b86df430a72 100644
>--- a/JSTests/stress/math-round-basics.js
>+++ b/JSTests/stress/math-round-basics.js
>@@ -69,6 +69,14 @@ for (var i = 0; i < 1e4; ++i) {
>     if (!(roundedValue === 0 && (1/roundedValue) === -Infinity))
>         throw "mathRoundOnDoubles(-0) = " + roundedValue;
> 
>+    var roundedValue = mathRoundOnDoubles(0.499999999999999944);
>+    if (!(roundedValue === 0 && (1/roundedValue) === Infinity))
>+        throw "mathRoundOnDoubles(0.499999999999999944) = " + roundedValue;
>+
>+    var roundedValue = mathRoundOnDoubles(-0.499999999999999944);
>+    if (!(roundedValue === 0 && (1/roundedValue) === -Infinity))
>+        throw "mathRoundOnDoubles(-0.499999999999999944) = " + roundedValue;
>+
>     var roundedValue = mathRoundOnDoubles(NaN);
>     if (roundedValue === roundedValue)
>         throw "mathRoundOnDoubles(NaN) = " + roundedValue;

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Attachments on bug 185115: 339079 | 339080 | 378145 | 378241