[Webkit-unassigned] [Bug 129486] Implement Math.hypot

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=129486


Darin Adler <darin at apple.com> changed:

           What    |Removed                     |Added
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 Attachment #226925|review?, commit-queue?      |review-, commit-queue-
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--- Comment #28 from Darin Adler <darin at apple.com>  2014-03-17 09:55:19 PST ---
(From update of attachment 226925)
View in context: https://bugs.webkit.org/attachment.cgi?id=226925&action=review

review- because of incorrect behavior when Infinity and NaN are combined

> LayoutTests/js/math-expected.txt:94
> +PASS Math.hypot(1, NaN, Infinity) is Infinity

Shouldn’t the expected result here be NaN, not Infinity?

> Source/JavaScriptCore/runtime/MathObject.cpp:113
> +    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "hypot"), 2, mathProtoFuncHypot, NoIntrinsic, DontEnum | Function);

No test coverage for the number of arguments? We should be testing that.

> Source/JavaScriptCore/runtime/MathObject.cpp:185
> +    Vector<double> args; 

We can get significantly better efficiency, avoiding heap allocation by saying:

    Vector<double, 8> args;

Choosing some number that is larger than the typical number of arguments passed to this function.

We should also do:

    args.reserveInitialCapacity(argsCount);

> Source/JavaScriptCore/runtime/MathObject.cpp:187
> +        args.append(exec->uncheckedArgument(i).toNumber(exec));

This can and should be args.uncheckedAppend if we use args.reserveInitialCapacity above.

> Source/JavaScriptCore/runtime/MathObject.cpp:191
> +        if (std::isinf(args[i]))
> +            return JSValue::encode(jsDoubleNumber(+std::numeric_limits<double>::infinity()));

Please remove this unless the behavior where we expect Infinity even if there is a NaN is correct. I do not believe it’s correct.

> Source/JavaScriptCore/runtime/MathObject.cpp:198
> +    // Kahan summation algorithm significantly reduces the numerical error in the total obtained.

I suggest putting this comment before the definitions of sum and compensation; they seem like part of the loop to me.

> Source/JavaScriptCore/runtime/MathObject.cpp:200
> +    for (unsigned i = 0; i < args.size(); ++i) {
> +        double scaledArgument = args[i] / max;

A nicer way to write this is:

    for (double argument : args) {
        double scaledArgument = argument / max;

No need for the use of "i" or "size".

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