linux-kernel - Re: [PATCH v3 08/16] MIPS: math-emu: <MAXA|MINA>.<D|S>: Fix cases of input values with opposite signs

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Date:   Fri, 21 Jul 2017 16:42:01 +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 08/16] MIPS: math-emu: <MAXA|MINA>.<D|S>: Fix cases of
 input values with opposite signs

On Fri, Jul 21, 2017 at 04:09:06PM +0200, Aleksandar Markovic wrote:
> From: Aleksandar Markovic <aleksandar.markovic@...tec.com>
> 
> Fix the value returned by <MAXA|MINA>.<D|S>, if inputs are normal fp
> numbers of the same absolute value, but opposite signs.
> 
> The relevant example:
> 
> MAXA.S fd,fs,ft:
>   If fs contains -3, and ft contains +3, fd is going to contain +3
>   (without this patch, it used to contain -3).

I think its worth mentioning also that for MINA.*, it returns the
negative one when the absolute values are equal (The phrase "For equal
absolute values, returns the smallest positive argument" in the manual
is a bit ambiguous IMO, so I ended up checking what I6500 did).

> 

Usual fixes/stable thing.

> 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>

Thanks
James

> ---
>  arch/mips/math-emu/dp_fmax.c | 8 ++++++--
>  arch/mips/math-emu/dp_fmin.c | 6 +++++-
>  arch/mips/math-emu/sp_fmax.c | 8 ++++++--
>  arch/mips/math-emu/sp_fmin.c | 6 +++++-
>  4 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/mips/math-emu/dp_fmax.c b/arch/mips/math-emu/dp_fmax.c
> index a0175cc..860b43f9 100644
> --- a/arch/mips/math-emu/dp_fmax.c
> +++ b/arch/mips/math-emu/dp_fmax.c
> @@ -224,7 +224,11 @@ union ieee754dp ieee754dp_fmaxa(union ieee754dp x, union ieee754dp y)
>  		return y;
>  
>  	/* Compare mantissa */
> -	if (xm <= ym)
> +	if (xm < ym)
>  		return y;
> -	return x;
> +	else if (xm > ym)
> +		return x;
> +	else if (xs == 0)
> +		return x;
> +	return y;
>  }
> diff --git a/arch/mips/math-emu/dp_fmin.c b/arch/mips/math-emu/dp_fmin.c
> index 074a858..73d85e4 100644
> --- a/arch/mips/math-emu/dp_fmin.c
> +++ b/arch/mips/math-emu/dp_fmin.c
> @@ -224,7 +224,11 @@ union ieee754dp ieee754dp_fmina(union ieee754dp x, union ieee754dp y)
>  		return x;
>  
>  	/* Compare mantissa */
> -	if (xm <= ym)
> +	if (xm < ym)
> +		return x;
> +	else if (xm > ym)
> +		return y;
> +	else if (xs == 1)
>  		return x;
>  	return y;
>  }
> diff --git a/arch/mips/math-emu/sp_fmax.c b/arch/mips/math-emu/sp_fmax.c
> index 15825db..fec7f64 100644
> --- a/arch/mips/math-emu/sp_fmax.c
> +++ b/arch/mips/math-emu/sp_fmax.c
> @@ -224,7 +224,11 @@ union ieee754sp ieee754sp_fmaxa(union ieee754sp x, union ieee754sp y)
>  		return y;
>  
>  	/* Compare mantissa */
> -	if (xm <= ym)
> +	if (xm < ym)
>  		return y;
> -	return x;
> +	else if (xm > ym)
> +		return x;
> +	else if (xs == 0)
> +		return x;
> +	return y;
>  }
> diff --git a/arch/mips/math-emu/sp_fmin.c b/arch/mips/math-emu/sp_fmin.c
> index f1418f7..74780bc 100644
> --- a/arch/mips/math-emu/sp_fmin.c
> +++ b/arch/mips/math-emu/sp_fmin.c
> @@ -225,7 +225,11 @@ union ieee754sp ieee754sp_fmina(union ieee754sp x, union ieee754sp y)
>  		return x;
>  
>  	/* Compare mantissa */
> -	if (xm <= ym)
> +	if (xm < ym)
> +		return x;
> +	else if (xm > ym)
> +		return y;
> +	else if (xs == 1)
>  		return x;
>  	return y;
>  }
> -- 
> 2.7.4
> 

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