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?
GCC defaults to -ffp-contract=fast which according to the manual:
> enables floating-point expression contraction
> such as forming of fused multiply-add operations if the target has
> native support for them
Which as Peter notes is not IEEE compliant.
Thanks,
Matt
--
Matthew Gretton-Dann
Linaro Toolchain Working Group
matthew.gretton-d...@linaro.org
_______________________________________________
linaro-toolchain mailing list
linaro-toolchain@lists.linaro.org
http://lists.linaro.org/mailman/listinfo/linaro-toolchain
