Re: [bug-gawk] atan2(y,x) return value for y = 0 and x = -0

[arnold]

I have a fix. I will send it out later today.

Thanks for the report.

Arnold
---------------------------------------
Hermann Peifer <address@hidden> wrote:

>
> Here a few more observations (as already posted to c.l.a)
>
> # The input value -0.0 (rather than -0) makes a difference
> $ awk -M 'BEGIN{ print atan2(-.0,-.0) }'
> -3.14159
>
> # Using the mpfr extension with input value -0
> $ awk -l mpfr 'BEGIN{ print mpfr_atan2(0,-0) }'
> 0.0000000000000000E-1
>
> # The trick with -0.0 doesn't help here
> $ awk -l mpfr 'BEGIN{ print mpfr_atan2(0,-.0) }'
> 0.0000000000000000E-1
>
> Hermann
>
> On 2014-01-18 15:05, Janis Papanagnou wrote:
> > Complementary to Herman's view I think that -0 should be handled as +0;
> > so I'd qualify the first sample below as "Why is the result pi here?", and
> > the second sample as "Works as expected". Either way, I agree that this
> > looks like a bug.
> >
> > Janis
> >
> >  > Date: Sat, 18 Jan 2014 14:56:19 +0100
> >  > From: address@hidden
> >  > To: address@hidden
> >  > CC: address@hidden
> >  > Subject: atan2(y,x) return value for y = 0 and x = -0
> >  >
> >  > Hi,
> >  >
> >  > This might be a feature or a bug, but I thought it would be worth
> > reporting.
> >  >
> >  > # Works as expected
> >  > $ awk 'BEGIN{ pi = atan2(0,-0) ; printf "%.16f\n", pi }'
> >  > 3.1415926535897931
> >  >
> >  > # Why is the result 0 here ?
> >  > $ awk -M 'BEGIN{ pi = atan2(0,-0) ; printf "%.16f\n", pi }'
> >  > 0.0000000000000000
> >  >
> >  > # Works again as expected
> >  > $ awk -M 'BEGIN{ pi = atan2(0,-0.1) ; printf "%.16f\n", pi }'
> >  > 3.1415926535897931
> >  >
> >  > # I used gawk from git on Mac OS X, 10.9.1
> >  > $ awk -V | head -1
> >  > GNU Awk 4.1.60, API: 1.0 (GNU MPFR 3.1.1-p2, GNU MP 5.1.2)
> >  >
> >  > Hermann
>