[FFmpeg-devel] cavs.c DECLARE_ALIGNED in ff_cavs_filter

[Reimar Döffinger]

On Mon, May 25, 2009 at 10:10:39AM +0000, Loren Merritt wrote:
> On Mon, 25 May 2009, M?ns Rullg?rd wrote:
> > Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
> >
> >> currently there is this code in cavs.c:
> >>     DECLARE_ALIGNED_8(uint8_t, bs[8]);
> >> The reason for it is that kind of code:
> >>> *((uint64_t *)bs) = 0x0202020202020202ULL;
> >>> if( *((uint64_t *)bs) ) {
> >>
> >> I thought of "solving" this via a union, but is this code really this
> >> speed critical that we need such a mess?
> >> Can't we just use memset for the writes and e.g. AV_RN64 for the read?
> 
> Are you complaining about the aliasing, or trying to simplify the code?

Actually about the DECLARE_ALIGNED_8 for a stack variable. 8 seems more
unlikely to cause issues than 16, but I am still trying to remove
that kind of stuff.

> > Such huge literals are fairly inefficient anyway on most CPUs.
> 
> As opposed to what? The compiler should emit the same code for memset as 
> for *(uint64_t*), and gcc on x86 does.

which would be an argument to use memset for simplicity, the read is a
slightly different question.
Btw. I know h264.c has the same code, but I don't want to mess with
that.