Date: Mon, 13 Nov 2017 17:43:51 -0800 From: John Baldwin <jhb@freebsd.org> To: freebsd-mips@freebsd.org Subject: Re: fabs(-0.0) returns -0.0 Message-ID: <2687660.XtxPXlZaqn@ralph.baldwin.cx> In-Reply-To: <CAPJvC9X2T23qZhWra8J__Fuo6000nxb-w61q5=i%2BBHmpXfmdmA@mail.gmail.com> References: <CAPJvC9X2T23qZhWra8J__Fuo6000nxb-w61q5=i%2BBHmpXfmdmA@mail.gmail.com>
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On Monday, November 13, 2017 10:52:10 PM Khilan Gudka wrote:
> Hi,
>
> The implementation of fabs(3) for MIPS (at least) appears to not be giving
> the right answer for when -0 is passed, as it returns -0 instead of +0. The
> implementation of fabs is:
>
> double fabs(double x) {
> if (x < 0)
> return -x;
> return x;
> }
>
> The if-test fails for -0 and thus it is returned. Is this a known issue? A
> simple fix would be to return x+0.0 instead of just x.
>
> The implication of this is that other functions which rely on fabs, such as
> hypot, also return -0. For example, hypot(-0.0, 0.0) returns -0 instead of
> +0.
The C version of fabs() for 32-bit arm has the same misimplementation btw.
All other architectures implement fabs in assembly in libc.
--
John Baldwin
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