On 9 October 2012 11:21, Matthew Gretton-Dann

<matthew.gretton-dann@linaro.org> wrote:
> On 9 October 2012 10:37, Jubi Taneja <jubitaneja@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?

-- PMM