linux-kernel - Re: [PATCH v3 10/16] MIPS: math-emu: MINA.<D|S>: Fix some cases of infinity and zero inputs

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Message-ID: <20170721160146.GO6973@jhogan-linux.le.imgtec.org>
Date:   Fri, 21 Jul 2017 17:01:46 +0100
From:   James Hogan <james.hogan@...tec.com>
To:     Aleksandar Markovic <aleksandar.markovic@...rk.com>
CC:     <linux-mips@...ux-mips.org>,
        Aleksandar Markovic <aleksandar.markovic@...tec.com>,
        Miodrag Dinic <miodrag.dinic@...tec.com>,
        Goran Ferenc <goran.ferenc@...tec.com>,
        Douglas Leung <douglas.leung@...tec.com>,
        <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 10/16] MIPS: math-emu: MINA.<D|S>: Fix some cases of
 infinity and zero inputs

On Fri, Jul 21, 2017 at 04:09:08PM +0200, Aleksandar Markovic wrote:
> From: Aleksandar Markovic <aleksandar.markovic@...tec.com>
> 
> Fix following special cases for MINA>.<D|S>:
> 
>   - if one of the inputs is zero, and the other is subnormal, normal,
>     or infinity, the  value of the former should be returned (that is,
>     a zero).
>   - if one of the inputs is infinity, and the other input is normal,
>     or subnormal, the value of the latter should be returned.
> 
> The previous implementation's logic for such cases was incorrect - it
> appears as if it implements MAXA, and not MINA instruction.
> 
> The relevant example:
> 
> MINA.S fd,fs,ft:
>   If fs contains 100.0, and ft contains 0.0, fd is going to contain
>   0.0 (without this patch, it used to contain 100.0).

Another ouch!

> 

Fixes/stable

> Signed-off-by: Miodrag Dinic <miodrag.dinic@...tec.com>
> Signed-off-by: Goran Ferenc <goran.ferenc@...tec.com>
> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@...tec.com>

Reviewed-by: James Hogan <james.hogan@...tec.com>

Cheers
James

> ---
>  arch/mips/math-emu/dp_fmin.c | 4 ++--
>  arch/mips/math-emu/sp_fmin.c | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/mips/math-emu/dp_fmin.c b/arch/mips/math-emu/dp_fmin.c
> index d4cd243..1e9ee3d 100644
> --- a/arch/mips/math-emu/dp_fmin.c
> +++ b/arch/mips/math-emu/dp_fmin.c
> @@ -191,14 +191,14 @@ union ieee754dp ieee754dp_fmina(union ieee754dp x, union ieee754dp y)
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
>  	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
> -		return x;
> +		return y;
>  
>  	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
> -		return y;
> +		return x;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
>  		return ieee754dp_zero(xs | ys);
> diff --git a/arch/mips/math-emu/sp_fmin.c b/arch/mips/math-emu/sp_fmin.c
> index 5f1d650..685ce75 100644
> --- a/arch/mips/math-emu/sp_fmin.c
> +++ b/arch/mips/math-emu/sp_fmin.c
> @@ -192,14 +192,14 @@ union ieee754sp ieee754sp_fmina(union ieee754sp x, union ieee754sp y)
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
>  	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
> -		return x;
> +		return y;
>  
>  	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
> -		return y;
> +		return x;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
>  		return ieee754sp_zero(xs | ys);
> -- 
> 2.7.4
> 

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