Hello Matthew,
2014-04-16 20:36 GMT+02:00 Matthew Brett <matthew.br...@gmail.com>:
> Hi,
>
> Sorry for my ignorance about mingw-w64 - I am hoping for advice on
> submitting a patch.
>
> When testing against the Python numpy library, we found a failing test
> for the mingw-w64 expm1 routine. Specifically, we found that:
>
> double i = -0.0;
> return expm1(i);
>
> returns 0 instead of -0, as I believe the standard requires:
>
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/expm1.html
> http://lists.gnu.org/archive/html/bug-gnulib/2012-03/msg00029.html
> https://github.com/gagern/gnulib/blob/master/tests/test-expm1-ieee.h
So thanks for showing to us this bug. Math tests are a bit wacky in
general. I use normally netbsd test for validation. Nevertheless
this works only in some aspects for Windows, so we have some
additional tests in our crt's testcases directory.
At this place I would think your testcase should go.
> The following patch fixes this:
>
> diff -r -u mingw-w64-v3.1.0/mingw-w64-crt/math/expm1.def.h
> b/mingw-w64-crt/math/expm1.def.h
> --- mingw-w64-v3.1.0/mingw-w64-crt/math/expm1.def.h 2014-04-14
> 20:41:33.000000000 -0700
> +++ b/mingw-w64-crt/math/expm1.def.h 2011-04-02 09:58:41.000000000 -0700
> @@ -60,7 +60,7 @@
> }
> else if (x_class == FP_ZERO)
> {
> - return __FLT_CST(0.0);
> + return (signbit (x) ? -__FLT_CST(0.0) : __FLT_CST(0.0)
Hmm, as x is in that case zero, wouldn't it be better just to return x here?
> }
> if (__FLT_ABI (fabs) (x) < __FLT_LOGE2)
> {
>
> but I don't know how to submit tests for the change. What do y'all advise?
>
> Thanks a lot,
A test checking exactly this case (or the set of cases for expm1) is welcome.
Please also provide an ChangeLog entry, so we can prominent mark your
code-donation.
> Matthew
Regards,
Kai
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