[FFmpeg-devel] AAC-Main (round 2)

[Dominik 'Rathann' Mierzejewski]

On Thursday, 20 November 2008 at 12:48, Dominik 'Rathann' Mierzejewski wrote:
> On Thursday, 20 November 2008 at 12:38, Robert Swain wrote:
> > 2008/11/20 M?ns Rullg?rd <mans at mansr.com>:
> > >
> > > Michael Niedermayer wrote:
> > >> On Thu, Nov 20, 2008 at 10:51:28AM -0000, M?ns Rullg?rd wrote:
> > >>>
> > >>> Michael Niedermayer wrote:
> > >>> > On Thu, Nov 20, 2008 at 10:25:51AM -0000, M?ns Rullg?rd wrote:
> > >>> >>
> > >>> >> Michael Niedermayer wrote:
> > >>> >> > On Wed, Nov 19, 2008 at 01:42:55PM -0500, Alex Converse wrote:
> > >>> >> > [...]
> > >>> >> >> diff --git a/libavcodec/aac.c b/libavcodec/aac.c
> > >>> >> >> index 1ad0a58..9fb242b 100644
> > >>> >> >> --- a/libavcodec/aac.c
> > >>> >> >> +++ b/libavcodec/aac.c
> > >>> >> >> @@ -91,6 +91,11 @@
> > >>> >> >>  #include <math.h>
> > >>> >> >>  #include <string.h>
> > >>> >> >>
> > >>> >> >> +#ifdef ARCH_X86
> > >>> >> >> +#define USE_754_PUNS
> > >>> >> >> +union float754 { float f; uint32_t i; };
> > >>> >> >> +#endif
> > >>> >> >
> > >>> >> > The correctness of the USE_754_PUNS code could be tested by configure
> > >>> >>
> > >>> >> Not easily.  The best we could do is set it based on architecture.
> > >>> >
> > >>> > hmm, is there a problem i miss with just compiling a
> > >>> > float a[]= {1.23456789, PI, E, -23.456789}
> > >>> > and checking if the IEEE expected byte sequence (for matching integer
> > >>> > endianness) is in the object file?
> > >>>
> > >>> That's checking 4 out of 4 billion possible float values.  Even if these
> > >>> look like IEEE754 numbers, there could be differences elsewhere, e.g.
> > >>> in the representation non-finite numbers.  Floating-point is weird enough
> > >>> that I wouldn't trust a simple check like that.
> > >>
> > >> A hand written list of archs wont be based on checking 4 billion values
> > >> each either. Nor would i completely trust a claim of manufactur X about their
> > >> cpus being Y compliant
> > >
> > > The list would include only architectures known to implement IEE754.  At
> > > the moment, this is all of the ones we support.
> > 
> > One would assume there's some sort of IEEE754 compliance test
> > somewhere by now. Is there?
> 
> I've just found this:
> http://www.cant.ua.ac.be/ieeecc754.html

And some more:
http://www.math.utah.edu/~beebe/software/ieee/

Regards,
R.

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