linux-kernel - Re: [PATCH v3 05/16] MIPS: math-emu: <MAX|MAXA|MIN|MINA>.<D|S>: Fix quiet NaN propagation

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Message-ID: <20170724134515.GV6973@jhogan-linux.le.imgtec.org>
Date:   Mon, 24 Jul 2017 14:45:15 +0100
From:   James Hogan <james.hogan@...tec.com>
To:     Aleksandar Markovic <Aleksandar.Markovic@...tec.com>
CC:     Aleksandar Markovic <aleksandar.markovic@...rk.com>,
        "linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
        Miodrag Dinic <Miodrag.Dinic@...tec.com>,
        Goran Ferenc <Goran.Ferenc@...tec.com>,
        Douglas Leung <Douglas.Leung@...tec.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Burton <Paul.Burton@...tec.com>,
        Petar Jovanovic <Petar.Jovanovic@...tec.com>,
        Raghu Gandham <Raghu.Gandham@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH v3 05/16] MIPS: math-emu: <MAX|MAXA|MIN|MINA>.<D|S>: Fix
 quiet NaN propagation

Hi Aleksandar,

On Mon, Jul 24, 2017 at 02:36:05PM +0100, Aleksandar Markovic wrote:
> > > diff --git a/arch/mips/math-emu/dp_fmax.c b/arch/mips/math-emu/dp_fmax.c
> > > index fd71b8d..567fc33 100644
> > > --- a/arch/mips/math-emu/dp_fmax.c
> > > +++ b/arch/mips/math-emu/dp_fmax.c
> > > @@ -47,6 +47,9 @@ union ieee754dp ieee754dp_fmax(union ieee754dp x, union ieee754dp y)
> > >       case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
> > >               return ieee754dp_nanxcpt(x);
> > >
> > > +     case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
> > > +             return x;
> > 
> > couldn't the above...
> > 
> > > +
> > >       /* numbers are preferred to NaNs */
> > >       case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
> > >       case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
> > > @@ -54,7 +57,6 @@ union ieee754dp ieee754dp_fmax(union ieee754dp x, union ieee754dp y)
> > 
> > ... go somewhere around here and fall through to the existing return x
> > case?
> > 
> 
> It could, but at the expense of code clarity and/or logical grouping of special cases,
> which after this patch looks like:
> 
>                . . .
>                  |
>   case of both inputs qNaN
>                  |
>   case of only x input qNaN
>                  |
>   case of only y input qNaN
>                  |
>                . . .
> 
> If you agree, I suggest keeping the code the same as currently proposed in
> this patch, except that the following comments should be added in appropriate
> places:
> 
> 	/*
> 	 * Quiet NaN handling
> 	 */
> 	/* The case of both inputs quiet NaNs */
>    . . .
> 	/* The cases of exactly one input quiet NaN */
> 
> Unfortunately, the code segment for handling of sNaN and infinity inputs do
> not follow the organization that I proposed. However, I think that my proposal
> for case organization is the superior one - therefore I intend to keep it in v4,
> unless you tell me not to do so.

Okay, I don't object.

Thanks
James

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