Date: Fri, 21 Jun 1996 19:41:19 +0200 (MET DST) From: "Christoph P. Kukulies" <kuku@gilberto.physik.rwth-aachen.de> To: bde@zeta.org.au (Bruce Evans) Cc: freebsd-hackers@FreeBSD.ORG, mrm@MARMOT.Mole.ORG Subject: Re: TARGET_NO_FANCY_MATH_387 Message-ID: <199606211741.TAA21575@gilberto.physik.rwth-aachen.de> In-Reply-To: <199605311508.BAA09743@godzilla.zeta.org.au> from Bruce Evans at "Jun 1, 96 01:08:37 am"
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> >Might it be a good thing now to change the default in gcc to enable
> >FP sin, cos and sqrt.
>
> It would only give the inline sqrt. The inline sin and cos are disabled
> in the FSF version of gcc-2.6.3 for other reasons. At least the i386
> versions of them were broken. You can use -mfancy-math-387 to get the
> inline sqrt and -ffast-math to get the inline sin and cos together with
> other fast and broken "math", or you can use inline assembler to get
> inline math functions exactly where you want, or you can use the i387
> version of libm to get non-inline hardware math functions in more cases.
Could you give an example showing that
-ffancy-math-386 and -ffast-math
have an effect? I tried with a small example and I'm always getting
calls instead of fpu-inline statements. (gcc-2.6.3)
#include <math.h>
main()
{
double d=2500.;
printf("%lf\n",sqrt(sin(d)));
}
gcc -ffast-math -m486 -mfancy-math-387 -S p.c
___gnu_compiled_c:
.text
LC0:
.ascii "%lf\12\0"
.align 4
.globl _main
.type _main,@function
_main:
pushl %ebp
movl %esp,%ebp
subl $8,%esp
call ___main
movl $0,-8(%ebp)
movl $1084459008,-4(%ebp)
pushl -4(%ebp)
pushl -8(%ebp)
call _sin
addl $8,%esp
subl $8,%esp
fstpl (%esp)
call _sqrt
> >for those of us with trusty '386/16's. Those still dependent upon
> >FP simulation could use -mno-fancy-math-387...
>
> The price of an i386 sqrt() emulation (in milliPentiums :-) has gone
> up. Those dependent on FP emulation would probably have difficulty
> bootstrapping to use it. At least the following utilities use sqrt(),
> so they might fail when their inline sqrt() doesn't work: as, awk, bc,
> cc1, cc1plus, dc, gdb, groff (parts), perl.
>
> >and document
> >-mfancy-math-387, -mno-fancy-math-387 in the man page for cc? ;-)
>
> They have been documented for 5 months in -current, and the changes were
> merged into -stable a couple of days ago.
>
> Bruce
>
--Chris Christoph P. U. Kukulies kuku@gil.physik.rwth-aachen.de
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