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Message-ID: <20170721150332.GK6973@jhogan-linux.le.imgtec.org>
Date: Fri, 21 Jul 2017 16:03:32 +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 06/16] MIPS: math-emu: <MAX|MAXA|MIN|MINA>.<D|S>: Fix
cases of both inputs zero
On Fri, Jul 21, 2017 at 04:09:04PM +0200, Aleksandar Markovic wrote:
> From: Aleksandar Markovic <aleksandar.markovic@...tec.com>
>
> 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@...tec.com>
> Signed-off-by: Goran Ferenc <goran.ferenc@...tec.com>
> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@...tec.com>
Otherwise
Reviewed-by: James Hogan <james.hogan@...tec.com>
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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