Re: [PATCH v3 12/16] MIPS: math-emu: <MADDF|MSUBF>.<D|S>: Fix some cases of infinite inputs

[James Hogan <james.hogan@imgtec.com>]

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On Fri, Jul 21, 2017 at 04:09:10PM +0200, Aleksandar Markovic wrote:
> From: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
> 
> Fix the cases of <MADDF|MSUBF>.<D|S> when any of two multiplicands is
> infinity. The correct behavior in such cases is affected by the nature
> of third input. Cases of addition of infinities with opposite signs
> and subtraction of infinities with same signs may arise and must be
> handles separately. Also, the value od flags argument (that determines

s/handles/handled/?
s/od/of/

> whether the instruction is MADDF or MSUBF) affects the outcome.
> 
> The relevant examples:
> 
> MADDF.S fd,fs,ft:
>   If fs contains +inf, ft contains +inf, and fd contains -inf, fd is
>   going to contain indef (without this patch, it used to contain
>   -inf).
>
> MSUBF.S fd,fs,ft:
>   If fs contains +inf, ft contains 1.0, and fd contains +0.0, fd is
>   going to contain -inf (without this patch, it used to contain +inf).
> 

Same fixes/stable notes as previous patch.

> Signed-off-by: Douglas Leung <douglas.leung@imgtec.com>
> Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com>
> Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com>
> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com>

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

Cheers
James

> ---
>  arch/mips/math-emu/dp_maddf.c | 21 ++++++++++++++++++++-
>  arch/mips/math-emu/sp_maddf.c | 21 ++++++++++++++++++++-
>  2 files changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/mips/math-emu/dp_maddf.c b/arch/mips/math-emu/dp_maddf.c
> index 4f2e783..45f815d 100644
> --- a/arch/mips/math-emu/dp_maddf.c
> +++ b/arch/mips/math-emu/dp_maddf.c
> @@ -85,7 +85,26 @@ static union ieee754dp _dp_maddf(union ieee754dp z, union ieee754dp x,
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
> -		return ieee754dp_inf(xs ^ ys);
> +		if ((zc == IEEE754_CLASS_INF) &&
> +		    ((!(flags & maddf_negate_product) && (zs != (xs ^ ys))) ||
> +		     ((flags & maddf_negate_product) && (zs == (xs ^ ys))))) {
> +			/*
> +			 * Cases of addition of infinities with opposite signs
> +			 * or subtraction of infinities with same signs.
> +			 */
> +			ieee754_setcx(IEEE754_INVALID_OPERATION);
> +			return ieee754dp_indef();
> +		}
> +		/*
> +		 * z is here either not infinity, or infinity of the same sign
> +		 * as maddf_negate_product * x * y. So, the result must be
> +		 * infinity, and its sign is determined only by the value of
> +		 * (flags & maddf_negate_product) and the signs of x and y.
> +		 */
> +		if (flags & maddf_negate_product)
> +			return ieee754dp_inf(1 ^ (xs ^ ys));
> +		else
> +			return ieee754dp_inf(xs ^ ys);
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
> diff --git a/arch/mips/math-emu/sp_maddf.c b/arch/mips/math-emu/sp_maddf.c
> index 9fd2035..76856d7 100644
> --- a/arch/mips/math-emu/sp_maddf.c
> +++ b/arch/mips/math-emu/sp_maddf.c
> @@ -86,7 +86,26 @@ static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
>  	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
> -		return ieee754sp_inf(xs ^ ys);
> +		if ((zc == IEEE754_CLASS_INF) &&
> +		    ((!(flags & maddf_negate_product) && (zs != (xs ^ ys))) ||
> +		     ((flags & maddf_negate_product) && (zs == (xs ^ ys))))) {
> +			/*
> +			 * Cases of addition of infinities with opposite signs
> +			 * or subtraction of infinities with same signs.
> +			 */
> +			ieee754_setcx(IEEE754_INVALID_OPERATION);
> +			return ieee754sp_indef();
> +		}
> +		/*
> +		 * z is here either not infinity, or infinity of the same sign
> +		 * as maddf_negate_product * x * y. So, the result must be
> +		 * infinity, and its sign is determined only by the value of
> +		 * (flags & maddf_negate_product) and the signs of x and y.
> +		 */
> +		if (flags & maddf_negate_product)
> +			return ieee754sp_inf(1 ^ (xs ^ ys));
> +		else
> +			return ieee754sp_inf(xs ^ ys);
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
> -- 
> 2.7.4
> 

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