RFR: 8255368: Math.exp() gives wrong result for large values on x86 32-bit platforms [v3]

[Xubo Zhang]

On Mon, 2 Nov 2020 17:42:27 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Xubo Zhang has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Merge branch 'JDK-8255368' of github.com:xbzhang99/bugfixes into JDK-8255368
>>  - Added test cases for exp at the value of 1024 and 10000
>
> 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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PR: https://git.openjdk.java.net/jdk/pull/894