RFR: 6506405: Math.abs(float) is slow [v7]

[Brian Burkhalter]

On Fri, 9 Jul 2021 22:02:14 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Brian Burkhalter has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR.
>
> src/java.base/share/classes/jdk/internal/math/DoubleConsts.java line 89:
> 
>> 87:                 ((SIGN_BIT_MASK & SIGNIF_BIT_MASK) == 0L) &&
>> 88:                 ((EXP_BIT_MASK & SIGNIF_BIT_MASK) == 0L)) &&
>> 89:                 ((SIGN_BIT_MASK | MAG_BIT_MASK) == ~0));
> 
> Nit: please use "~0L" instead so the long-ness of 0 is explicit.

Fixed.

> test/jdk/java/lang/Math/AbsTests.java line 202:
> 
>> 200:             return Float.floatToRawIntBits(result) !=
>> 201:                 Float.floatToRawIntBits(f) ? 1 : 0;
>> 202:         } else if ((f >= 0 && result != f) || (f < 0 && result != -f)) {
> 
> Please look at the Tests.java file in the jdk/test/java/lang/Math directory. One of the methods like
> 
>     public static int test(String testName, double input,
>                            double result, double expected
> 
> will be helpful here; e.g.
> 
> Tests.test("Math.abs", f, Math.abs(-f), f)
> 
> I would also add combination for StrictMath.abs and negations:
> 
> Tests.test("Math.abs", f, Math.abs(f), f)
> Tests.test("StrictMath.abs", -f, Math.abs(f), f)
> Tests.test("StrictMath.abs", f, Math.abs(f), f)

Modified.

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PR: https://git.openjdk.java.net/jdk/pull/4711