[FFmpeg-devel] [PATCH 7/7] Add alias-safe aligned AV_[RW]N macros

[Michael Niedermayer]

On Sun, Feb 07, 2010 at 01:06:41PM +0000, M?ns Rullg?rd wrote:
> Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
> 
> > On Fri, Feb 05, 2010 at 10:51:59AM +0100, Michael Niedermayer wrote:
> >> On Sun, Jan 31, 2010 at 02:08:29AM +0000, M?ns Rullg?rd wrote:
> >> > Michael Niedermayer <michaelni at gmx.at> writes:
> >> > 
> >> > > On Fri, Jan 29, 2010 at 02:12:14AM +0000, Mans Rullgard wrote:
> >> > >> ---
> >> > >>  libavutil/intreadwrite.h |   32 ++++++++++++++++++++++++++++++++
> >> > >>  1 files changed, 32 insertions(+), 0 deletions(-)
> >> > >> 
> >> > >> diff --git a/libavutil/intreadwrite.h b/libavutil/intreadwrite.h
> >> > >> index 631db75..61ad488 100644
> >> > >> --- a/libavutil/intreadwrite.h
> >> > >> +++ b/libavutil/intreadwrite.h
> >> > >> @@ -418,6 +418,38 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
> >> > >>      } while(0)
> >> > >>  #endif
> >> > >>  
> >> > >> +/*
> >> > >> + * The AV_[RW]NA macros access naturally aligned data
> >> > >> + * in a type-safe way.
> >> > >> + */
> >> > >> +
> >> > >> +#define AV_RNA(s, p)    (((const ff_alias##s*)(p))->u##s)
> >> > >> +#define AV_WNA(s, p, v) (((ff_alias##s*)(p))->u##s = (v))
> >> > >
> >> > > do we really need yet another set?
> >> > 
> >> > We need one set for aligned accesses and one for unaligned, yes.
> >> 
> >> yes i agree, doesnt mean i like it though
> >
> > What I don't particularly like is that "NA" is a bit confusing, unless
> > you extrapolate from the other naming it might just as well mean "not aligned".
> > No, I don't have better ideas...
> 
> We could rename the other ones into AV_[RW]*U...

or always inlude the U / A, this would decrease the chance of people using
AV_[RW] and expectings its alignment requirements to be different from
what they are

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Into a blind darkness they enter who follow after the Ignorance,
they as if into a greater darkness enter who devote themselves
to the Knowledge alone. -- Isha Upanishad
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