RFR: 8255368: Math.exp() gives wrong result for large values on x86 32-bit platforms [v5]

[Xubo Zhang]

On Mon, 9 Nov 2020 22:10:07 GMT, Xubo Zhang <github.com+58006833+xbzhang99 at openjdk.org> wrote:

>> The regression tests for exp should be explicitly updated to cover the previously erroneous input if they do not do so already.
>
> Hi Darcy,
> Where should the test be? A new test file?
> 
> Best regards,
> Xubo
> 
> From: Joe Darcy <notifications at github.com>
> Sent: Monday, November 9, 2020 1:33 PM
> To: openjdk/jdk <jdk at noreply.github.com>
> Cc: Zhang, Xubo <xubo.zhang at intel.com>; Mention <mention at noreply.github.com>
> Subject: Re: [openjdk/jdk] 8255368: Math.exp() gives wrong result for large values on x86 32-bit platforms (#894)
> 
> 
> @jddarcy commented on this pull request.
> 
> ________________________________
> 
> In test/jdk/java/lang/Math/WorstCaseTests.java<https://github.com/openjdk/jdk/pull/894#discussion_r520133623>:
> 
>> @@ -114,8 +114,8 @@ private static int testWorstExp() {
> 
>              {+0x1.A8EAD058BC6B8p3,      0x1.1D71965F516ADp19},
> 
>              {+0x1.1D5C2DAEBE367p4,      0x1.A8C02E974C314p25},
> 
>              {+0x1.C44CE0D716A1Ap4,      0x1.B890CA8637AE1p40},
> 
> -            {+0x4.0p8,                  Double.POSITIVE_INFINITY},
> 
> -            {+0x2.71p12,                Double.POSITIVE_INFINITY},
> 
> +            {+0x4.0p8,                  Double.POSITIVE_INFINITY}, //bug 8255368 gave 0
> 
> This is not an appropriate test to update to cover this bug. This test is specifically probing at difficult cases in double arithmetic for the underlying mathematically function as opposed to flaws in a particular implementation.
> 
> —
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Sure. 
I reversed the changes in WorstCaseTests.java, and added a new test file ExpCornerCaseTests.java in test/jdk/java/lang/Math

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PR: https://git.openjdk.java.net/jdk/pull/894