Re: [PATCH v3 06/16] MIPS: math-emu: <MAX|MAXA|MIN|MINA>.<D|S>: Fix cases of both inputs zero

[James Hogan]

On Fri, Jul 21, 2017 at 04:09:04PM +0200, Aleksandar Markovic wrote:
> From: Aleksandar Markovic <aleksandar.markovic@xxxxxxxxxx>
> 
> Fix the value returned by <MAX|MAXA|MIN|MINA>.<D|S>, if both inputs
> are zeros. The right behavior in such cases is stated in instruction
> reference manual and is as follows:
> 
>    fs  ft       MAX     MIN       MAXA    MINA
>   ---------------------------------------------
>     0   0        0       0         0       0
>     0  -0        0      -0         0      -0
>    -0   0        0      -0         0      -0
>    -0  -0       -0      -0        -0      -0

To be fair I think the min behaviour was already technically correct.
When the values matched it returned that value, and when they didn't
match it returned -0, so max could have just been fixed to return
ieee754*p_zero(0), but its fine IMO to rewrite both like you have.

> 
> The relevant example:
> 
> MAX.S fd,fs,ft:
>   If fs contains +0, and ft contains -0, fd is going to contain 0
>   (without this patch, it used to contain -0).
> 

Consider Fixes and Cc stable as with other patch

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

Otherwise
Reviewed-by: James Hogan <james.hogan@xxxxxxxxxx>

Cheers
James

> ---
>  arch/mips/math-emu/dp_fmax.c | 8 ++------
>  arch/mips/math-emu/dp_fmin.c | 8 ++------
>  arch/mips/math-emu/sp_fmax.c | 8 ++------
>  arch/mips/math-emu/sp_fmin.c | 8 ++------
>  4 files changed, 8 insertions(+), 24 deletions(-)
> 
> diff --git a/arch/mips/math-emu/dp_fmax.c b/arch/mips/math-emu/dp_fmax.c
> index 567fc33..9517572 100644
> --- a/arch/mips/math-emu/dp_fmax.c
> +++ b/arch/mips/math-emu/dp_fmax.c
> @@ -82,9 +82,7 @@ union ieee754dp ieee754dp_fmax(union ieee754dp x, union ieee754dp y)
>  		return ys ? x : y;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754dp_zero(1);
> +		return ieee754dp_zero(xs & ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		DPDNORMX;
> @@ -184,9 +182,7 @@ union ieee754dp ieee754dp_fmaxa(union ieee754dp x, union ieee754dp y)
>  		return y;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754dp_zero(1);
> +		return ieee754dp_zero(xs & ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		DPDNORMX;
> diff --git a/arch/mips/math-emu/dp_fmin.c b/arch/mips/math-emu/dp_fmin.c
> index 77f7ca9..7069320 100644
> --- a/arch/mips/math-emu/dp_fmin.c
> +++ b/arch/mips/math-emu/dp_fmin.c
> @@ -82,9 +82,7 @@ union ieee754dp ieee754dp_fmin(union ieee754dp x, union ieee754dp y)
>  		return ys ? y : x;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754dp_zero(1);
> +		return ieee754dp_zero(xs | ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		DPDNORMX;
> @@ -184,9 +182,7 @@ union ieee754dp ieee754dp_fmina(union ieee754dp x, union ieee754dp y)
>  		return y;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754dp_zero(1);
> +		return ieee754dp_zero(xs | ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		DPDNORMX;
> diff --git a/arch/mips/math-emu/sp_fmax.c b/arch/mips/math-emu/sp_fmax.c
> index d46e8e4..d72111a 100644
> --- a/arch/mips/math-emu/sp_fmax.c
> +++ b/arch/mips/math-emu/sp_fmax.c
> @@ -82,9 +82,7 @@ union ieee754sp ieee754sp_fmax(union ieee754sp x, union ieee754sp y)
>  		return ys ? x : y;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754sp_zero(1);
> +		return ieee754sp_zero(xs & ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		SPDNORMX;
> @@ -184,9 +182,7 @@ union ieee754sp ieee754sp_fmaxa(union ieee754sp x, union ieee754sp y)
>  		return y;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754sp_zero(1);
> +		return ieee754sp_zero(xs & ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		SPDNORMX;
> diff --git a/arch/mips/math-emu/sp_fmin.c b/arch/mips/math-emu/sp_fmin.c
> index b528c4b..61ff9c6 100644
> --- a/arch/mips/math-emu/sp_fmin.c
> +++ b/arch/mips/math-emu/sp_fmin.c
> @@ -82,9 +82,7 @@ union ieee754sp ieee754sp_fmin(union ieee754sp x, union ieee754sp y)
>  		return ys ? y : x;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754sp_zero(1);
> +		return ieee754sp_zero(xs | ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		SPDNORMX;
> @@ -184,9 +182,7 @@ union ieee754sp ieee754sp_fmina(union ieee754sp x, union ieee754sp y)
>  		return y;
>  
>  	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> -		if (xs == ys)
> -			return x;
> -		return ieee754sp_zero(1);
> +		return ieee754sp_zero(xs | ys);
>  
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
>  		SPDNORMX;
> -- 
> 2.7.4
>

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