Re: [PATCH v3 13/16] MIPS: math-emu: <MADDF|MSUBF>.<D|S>: Fix some cases of zero inputs

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

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On Fri, Jul 21, 2017 at 04:09:11PM +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
> +0 or -0, and the third input is also +0 or -0. Depending on the signs
> of inputs, certain special cases must be handled.
> 
> The relevant example:
> 
> MADDF.S fd,fs,ft:
>   If fs contains +0.0, ft contains -0.0, and fd contains 0.0, fd is
>   going to contain +0.0 (without this patch, it used to contain -0.0).
> 

Usual fixes/stable comments.

> 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>

Patch looks correct to me.

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

Cheers
James

> ---
>  arch/mips/math-emu/dp_maddf.c | 8 ++++++++
>  arch/mips/math-emu/sp_maddf.c | 8 ++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/arch/mips/math-emu/dp_maddf.c b/arch/mips/math-emu/dp_maddf.c
> index 45f815d..b8b2c17 100644
> --- a/arch/mips/math-emu/dp_maddf.c
> +++ b/arch/mips/math-emu/dp_maddf.c
> @@ -113,6 +113,14 @@ static union ieee754dp _dp_maddf(union ieee754dp z, union ieee754dp x,
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
>  		if (zc == IEEE754_CLASS_INF)
>  			return ieee754dp_inf(zs);
> +		/* Handle cases +0 + (-0) and similar ones. */
> +		if (zc == IEEE754_CLASS_ZERO) {
> +			if ((!(flags & maddf_negate_product) && (zs == (xs ^ ys))) ||
> +			    ((flags & maddf_negate_product) && (zs != (xs ^ ys))))
> +				return z;
> +			else
> +				return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
> +		}
>  		/* Multiplication is 0 so just return z */
>  		return z;
>  
> diff --git a/arch/mips/math-emu/sp_maddf.c b/arch/mips/math-emu/sp_maddf.c
> index 76856d7..cb8597b 100644
> --- a/arch/mips/math-emu/sp_maddf.c
> +++ b/arch/mips/math-emu/sp_maddf.c
> @@ -114,6 +114,14 @@ static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
>  	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
>  		if (zc == IEEE754_CLASS_INF)
>  			return ieee754sp_inf(zs);
> +		/* Handle cases +0 + (-0) and similar ones. */
> +		if (zc == IEEE754_CLASS_ZERO) {
> +			if ((!(flags & maddf_negate_product) && (zs == (xs ^ ys))) ||
> +			    ((flags & maddf_negate_product) && (zs != (xs ^ ys))))
> +				return z;
> +			else
> +				return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);
> +		}
>  		/* Multiplication is 0 so just return z */
>  		return z;
>  
> -- 
> 2.7.4
> 

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