Re: [PATCH v3 11/16] MIPS: math-emu: <MADDF|MSUBF>.<D|S>: Fix NaN propagation

From: James Hogan
Date: Mon Jul 24 2017 - 06:24:51 EST

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On Fri, Jul 21, 2017 at 04:09:09PM +0200, Aleksandar Markovic wrote:
> From: Aleksandar Markovic <aleksandar.markovic@xxxxxxxxxx>
>
> Fix the cases of <MADDF|MSUBF>.<D|S> when any of three inputs is any
> NaN. Correct behavior of <MADDF|MSUBF>.<D|S> fd, fs, ft is following:
>
> - if any of inputs is sNaN, return a sNaN using following rules: if
> only one input is sNaN, return that one; if more than one input is
> sNaN, order of precedence for return value is fd, fs, ft
> - if no input is sNaN, but at least one of inputs is qNaN, return a
> qNaN using following rules: if only one input is qNaN, return that
> one; if more than one input is qNaN, order of precedence for
> return value is fd, fs, ft
>
> The previous code contained handling of some above cases, but not all.
> Also, such handling was scattered into various cases of
> "switch (CLPAIR(xc, yc))" statement and elsewhere. With this patch,
> this logic is placed in one place, and "switch (CLPAIR(xc, yc))" is
> significantly simplified.
>
> The relevant example:
>
> MADDF.S fd,fs,ft:
> If fs contains qNaN1, ft contains qNaN2, and fd contains qNaN3, fd
> is going to contain qNaN3 (without this patch, it used to contain
> qNaN1).
>

Fixes: e24c3bec3e8e ("MIPS: math-emu: Add support for the MIPS R6 MADDF FPU instruction")
Fixes: 83d43305a1df ("MIPS: math-emu: Add support for the MIPS R6 MSUBF FPU instruction")

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

If backported, I suspect commits:
6162051e87f6 ("MIPS: math-emu: Unify ieee754sp_m{add,sub}f")
and
d728f6709bcc ("MIPS: math-emu: Unify ieee754dp_m{add,sub}f")
in 4.7 will require manual backporting between 4.3 and 4.7 (due to
separation of maddf/msubf before that point), so I suppose tagging
stable 4.7+ and backporting is best (assuming you consider this fix
worth backporting).

> ---
> arch/mips/math-emu/dp_maddf.c | 71 ++++++++++++++-----------------------------
> arch/mips/math-emu/sp_maddf.c | 69 ++++++++++++++---------------------------
> 2 files changed, 46 insertions(+), 94 deletions(-)
>
> diff --git a/arch/mips/math-emu/dp_maddf.c b/arch/mips/math-emu/dp_maddf.c
> index caa62f2..4f2e783 100644
> --- a/arch/mips/math-emu/dp_maddf.c
> +++ b/arch/mips/math-emu/dp_maddf.c
> @@ -48,52 +48,35 @@ static union ieee754dp _dp_maddf(union ieee754dp z, union ieee754dp x,
>
> ieee754_clearcx();
>
> - switch (zc) {
> - case IEEE754_CLASS_SNAN:
> - ieee754_setcx(IEEE754_INVALID_OPERATION);
> - return ieee754dp_nanxcpt(z);
> - case IEEE754_CLASS_DNORM:
> - DPDNORMZ;
> - /* QNAN and ZERO cases are handled separately below */
> - }
> -
> - switch (CLPAIR(xc, yc)) {
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
> - return ieee754dp_nanxcpt(y);
> -
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
> - return ieee754dp_nanxcpt(x);
> -
> - case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
> + /* handle the cases when at least one of x, y or z is a NaN */
> + if (((xc == IEEE754_CLASS_SNAN) || (xc == IEEE754_CLASS_QNAN)) ||
> + ((yc == IEEE754_CLASS_SNAN) || (yc == IEEE754_CLASS_QNAN)) ||
> + ((zc == IEEE754_CLASS_SNAN) || (zc == IEEE754_CLASS_QNAN))) {

This condition basically covers all of the cases below. Any particular
reason not to skip it ...

> + /* order of precedence is z, x, y */
> + if (zc == IEEE754_CLASS_SNAN)
> + return ieee754dp_nanxcpt(z);
> + if (xc == IEEE754_CLASS_SNAN)
> + return ieee754dp_nanxcpt(x);
> + if (yc == IEEE754_CLASS_SNAN)
> + return ieee754dp_nanxcpt(y);
> + if (zc == IEEE754_CLASS_QNAN)
> + return z;
> + if (xc == IEEE754_CLASS_QNAN)
> + return x;
> return y;

... and make this return conditional on (yc == IEEE754_CLASS_QNAN)?

Same for sp_maddf.c too.

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

Cheers
James

> + }
>
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
> - return x;
> + if (zc == IEEE754_CLASS_DNORM)
> + DPDNORMZ;
> + /* ZERO z cases are handled separately below */
>
> + switch (CLPAIR(xc, yc)) {
>
> /*
> * Infinity handling
> */
> case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
> case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> ieee754_setcx(IEEE754_INVALID_OPERATION);
> return ieee754dp_indef();
>
> @@ -102,8 +85,6 @@ 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):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> return ieee754dp_inf(xs ^ ys);
>
> case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> @@ -120,25 +101,19 @@ static union ieee754dp _dp_maddf(union ieee754dp z, union ieee754dp x,
> DPDNORMX;
>
> case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> - else if (zc == IEEE754_CLASS_INF)
> + if (zc == IEEE754_CLASS_INF)
> return ieee754dp_inf(zs);
> DPDNORMY;
> break;
>
> case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> - else if (zc == IEEE754_CLASS_INF)
> + if (zc == IEEE754_CLASS_INF)
> return ieee754dp_inf(zs);
> DPDNORMX;
> break;
>
> case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> - else if (zc == IEEE754_CLASS_INF)
> + if (zc == IEEE754_CLASS_INF)
> return ieee754dp_inf(zs);
> /* fall through to real computations */
> }
> diff --git a/arch/mips/math-emu/sp_maddf.c b/arch/mips/math-emu/sp_maddf.c
> index c91d5e5..9fd2035 100644
> --- a/arch/mips/math-emu/sp_maddf.c
> +++ b/arch/mips/math-emu/sp_maddf.c
> @@ -48,51 +48,36 @@ static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
>
> ieee754_clearcx();
>
> - switch (zc) {
> - case IEEE754_CLASS_SNAN:
> - ieee754_setcx(IEEE754_INVALID_OPERATION);
> - return ieee754sp_nanxcpt(z);
> - case IEEE754_CLASS_DNORM:
> - SPDNORMZ;
> - /* QNAN and ZERO cases are handled separately below */
> + /* handle the cases when at least one of x, y or z is a NaN */
> + if (((xc == IEEE754_CLASS_SNAN) || (xc == IEEE754_CLASS_QNAN)) ||
> + ((yc == IEEE754_CLASS_SNAN) || (yc == IEEE754_CLASS_QNAN)) ||
> + ((zc == IEEE754_CLASS_SNAN) || (zc == IEEE754_CLASS_QNAN))) {
> + /* order of precedence is z, x, y */
> + if (zc == IEEE754_CLASS_SNAN)
> + return ieee754sp_nanxcpt(z);
> + if (xc == IEEE754_CLASS_SNAN)
> + return ieee754sp_nanxcpt(x);
> + if (yc == IEEE754_CLASS_SNAN)
> + return ieee754sp_nanxcpt(y);
> + if (zc == IEEE754_CLASS_QNAN)
> + return z;
> + if (xc == IEEE754_CLASS_QNAN)
> + return x;
> + return y;
> }
>
> + if (zc == IEEE754_CLASS_DNORM)
> + SPDNORMZ;
> + /* ZERO z cases are handled separately below */
> +
> switch (CLPAIR(xc, yc)) {
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
> - return ieee754sp_nanxcpt(y);
> -
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
> - case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
> - return ieee754sp_nanxcpt(x);
> -
> - case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
> - return y;
>
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
> - case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
> - return x;
>
> /*
> * Infinity handling
> */
> case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
> case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> ieee754_setcx(IEEE754_INVALID_OPERATION);
> return ieee754sp_indef();
>
> @@ -101,8 +86,6 @@ 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):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> return ieee754sp_inf(xs ^ ys);
>
> case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
> @@ -119,25 +102,19 @@ static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
> SPDNORMX;
>
> case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> - else if (zc == IEEE754_CLASS_INF)
> + if (zc == IEEE754_CLASS_INF)
> return ieee754sp_inf(zs);
> SPDNORMY;
> break;
>
> case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> - else if (zc == IEEE754_CLASS_INF)
> + if (zc == IEEE754_CLASS_INF)
> return ieee754sp_inf(zs);
> SPDNORMX;
> break;
>
> case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
> - if (zc == IEEE754_CLASS_QNAN)
> - return z;
> - else if (zc == IEEE754_CLASS_INF)
> + if (zc == IEEE754_CLASS_INF)
> return ieee754sp_inf(zs);
> /* fall through to real computations */
> }
> --
> 2.7.4
>

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