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