On Friday 28 July 2006 01:51, David Miller wrote:
> From: Rene Rebe <rene@xxxxxxxxxxxx>
> Date: Mon, 26 Jun 2006 09:02:12 +0200
>
> > int main ()
> > {
> > long double a = 2;
> > long double b = 1.0;
> > a *= b;
> > printf ("%Lf\n", a);
> > }
> >
> > built with: gcc -m64 -mhard-quad-float
> >
> > yields: 4
>
> Something is wrong with _FP_MUL_MEAT_2_wide_3mul, which tries to
> optimize the 2-limb multiply into 3 multiplies instead of 4. None of
> the other platforms utilizing the soft-fp layer in the kernel try to
> use the _3mul version either.
>
> Correctness trumps performance, so we can just use the full 4 multiply
> version to fix this bug.
>
> Thanks for the report.
>
> diff-tree 92f282988b4ce3967ee8399f7d1184ebfa04e48b (from 64821324ca49f24be1a66f2f432108f96a24e596)
> Author: David S. Miller <davem@xxxxxxxxxxxxxxxxxxxx>
> Date: Thu Jul 27 16:49:21 2006 -0700
>
> [SPARC64]: Fix quad-float multiply emulation.
>
> Something is wrong with the 3-multiply (vs. 4-multiply) optimized
> version of _FP_MUL_MEAT_2_*(), so just use the slower version
> which actually computes correct values.
>
> Noticed by Rene Rebe
>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
>
> diff --git a/include/asm-sparc64/sfp-machine.h b/include/asm-sparc64/sfp-machine.h
> index 5015bb8..89d4243 100644
> --- a/include/asm-sparc64/sfp-machine.h
> +++ b/include/asm-sparc64/sfp-machine.h
> @@ -34,7 +34,7 @@
> #define _FP_MUL_MEAT_D(R,X,Y) \
> _FP_MUL_MEAT_1_wide(_FP_WFRACBITS_D,R,X,Y,umul_ppmm)
> #define _FP_MUL_MEAT_Q(R,X,Y) \
> - _FP_MUL_MEAT_2_wide_3mul(_FP_WFRACBITS_Q,R,X,Y,umul_ppmm)
> + _FP_MUL_MEAT_2_wide(_FP_WFRACBITS_Q,R,X,Y,umul_ppmm)
>
> #define _FP_DIV_MEAT_S(R,X,Y) _FP_DIV_MEAT_1_imm(S,R,X,Y,_FP_DIV_HELP_imm)
> #define _FP_DIV_MEAT_D(R,X,Y) _FP_DIV_MEAT_1_udiv_norm(D,R,X,Y)
>
I can confirm this patch corrects the emulation.
Yours thankfully,
--
René Rebe - ExactCODE - Berlin (Europe / Germany)
http://exactcode.de | http://t2-project.org | http://rene.rebe.name
+49 (0)30 / 255 897 45
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