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Date: Mon, 23 Jul 2018 12:34:18 -0700
From: Steve Kargl <sgk@troutmask.apl.washington.edu>
To: enh via freebsd-numerics <freebsd-numerics@freebsd.org>
Subject: Re: fmod nan_mix usage
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References: <CAJgzZopb_0fxM9jbVjUEZ0JPOfcrgeQo_Ki-afZ5aRNr38tKVg@mail.gmail.com>
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On Mon, Jul 23, 2018 at 11:28:08AM -0700, enh via freebsd-numerics wrote:
> the recent change from
> 
>   return (x*y)/(x*y);
> 
> to
> 
>   return nan_mix(x, y)/nan_mix(x, y);
> 
> in e_fmod.c broke some of our unit tests. for example, fmod(3.f, 0.f) in
> one of the VM tests.
> 
> bionic/tests/math_test.cpp:(784) Failure in test
> math_h_force_long_double.fmod
> Value of: isnan(fmod(3.0, 0.0))
>   Actual: false
> Expected: true

Can you share the code for the relevant tests?
This simple program gives the expected results
on amd64.

#include <math.h>
#include <stdio.h>

int
main(void)
{
	printf("%e %d\n", fmodf(3.f, 0.f), isnan(fmodf(3.f, 0.f)));
	printf("%le %d\n", fmod(3.0, 0.0),  isnan(fmod(3.0, 0.0)));
	printf("%Le %d\n", fmodl(3.L, 0.L),  isnan(fmodl(3.L, 0.L)));
	return 0;
}

% cc -o z -O a.c -lm && ./z
nan 1
nan 1
nan 1

-- 
Steve