__m128 data type *not* auto aligned with GCC. :-/

__m128 data type *not* auto aligned with GCC. :-/

[Ozzy]

Hi,

I'm working on a port from a win32 prg to linux.
My last problem is due to automatic data alignment under VisualC++ or
ICC when u are
using __m128 data types inside your sets of structures. In fact, i
haven't been able to get
the right/same structure bytes fields organisation with GCC while using
:

__attribute__((aligned(16)))
is this aligning something??????

or

#pragma pack(push,16)
(may get same structure size but not exactly padded as it was intended)

or

the combination of both but it doesn't work aswell. ;)

Anyhow, any help is welcome on the subject! I hope that 3.3 will fix
that problem which makes Instrinsics code portability a real nightmare!
:)=

bye,

Ozzy.

Re: __m128 data type *not* auto aligned with GCC. :-/

[Arunachalam G]

Hi,

On Mon, 30 Dec 2002, Ozzy wrote:
> Hi,
>
[...]
> using __m128 data types inside your sets of structures. In fact, i
> haven't been able to get
> the right/same structure bytes fields organisation with GCC while using
> :
> __attribute__((aligned(16)))
> is this aligning something??????
>
Yes, this does aligning if the object globally visible.

eg.

int gi __attribute__ ((aligned(128)));

main()
{
     int i __attribute__ ((aligned(128)));
}

the variable gi will be aligned to 128bytes boundary not the
variable i even though it is requested. You can check this with
__alignof__ operator. Alignment can't be done in stack area.


Sincerely,
Arunachalam.