On Tue, Oct 9, 2012 at 5:16 PM, Mans Rullgard <mans.rullg...@linaro.org>wrote:
> On 9 October 2012 12:09, Peter Maydell <peter.mayd...@linaro.org> wrote:
> > On 9 October 2012 11:21, Matthew Gretton-Dann
> > <matthew.gretton-d...@linaro.org> wrote:
> >> On 9 October 2012 10:37, Jubi Taneja <jubitan...@gmail.com> wrote:
> >>> I wanted to see the difference in objdump of an application where I
> can make
> >>> the difference between the VFPV3 and VFPV4 support. I tried enabling
> the
> >>> flag -mfpu=vfpv3 and -mfpu=vfpv4 for ARM Cortex A15 toolchain in my
> test
> >>> code but cannot see the difference in two objdumps.
> >>
> >> Try the following (tested against FSF GCC:
> >>
> >> /* arm-none-linux-gnueabi-gcc -mcpu=cortex-a15 -mfpu=vfpv4 -S -o-
> >> /tmp/fma.c -mfloat-abi=hard -O2 */
> >> float f(float a, float b, float c)
> >> {
> >> return a * b + c;
> >> }
> >> /* end of tmp.c */
> >
> > I would have expected that you would need a gcc option to tell it that
> > non-IEEE floating point results are OK. Otherwise it's not valid to
> > emit a fused multiply-add for a*b+c because IEEE specifies that you
> > should get a rounding step between the multiply and the add. Or
> > does gcc default to non-IEEE arithmetic?
>
> Maybe adding -ffast-math does something.
>
I have checked, it does not make any difference.
>
> --
> Mans Rullgard / mru
>
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