[FFmpeg-devel] [PATCH] lavu/eval: add ifzero() and ifnonzero() expression

[Stefano Sabatini]

On date Monday 2012-01-16 00:37:35 +0100, Michael Niedermayer encoded:
> On Sun, Jan 15, 2012 at 11:08:55PM +0100, Stefano Sabatini wrote:
> > They allow to implement the if/then/else logic, which cannot be
> > implemented otherwise.
> > 
> > For example the expression:
> > A*B + not(A)*C
> > 
> > always evaluates to NaN if B is NaN, even in the case where A is 0.
> > ---
> >  doc/eval.texi    |   19 ++++++++++++-------
> >  libavutil/eval.c |    8 ++++++++
> >  2 files changed, 20 insertions(+), 7 deletions(-)
> > 
> > diff --git a/doc/eval.texi b/doc/eval.texi
> > index b325b37..4cc8ec9 100644
> > --- a/doc/eval.texi
> > +++ b/doc/eval.texi
> > @@ -100,6 +100,14 @@ Return the greatest common divisor of @var{x} and @var{y}. If both @var{x} and
> >  @var{y} are 0 or either or both are less than zero then behavior is undefined.
> >  @end table
> >  
> > + at item ifzero(x, y)
> > +Evaluate @var{x}, and if the result is zero return the result of the
> > +evaluation of @var{y}, return 0 otherwise.
> > +
> > + at item ifnonzero(x, y)
> > +Evaluate @var{x}, and if the result is non-zero return the result of
> > +the evaluation of @var{y}, return 0 otherwise.
> 
> i suggest
> 
> if(x,y)
> Evaluates y when x is non zero
> returns the value of y if evaluated otherwise 0
> 
> then
> if(not(x),y)
> would give the other case

Works for me, I'm keeping ifnot() since it slightly simplifies syntax
(if(not(x),y) -> ifnot(x,y)).
-- 
FFmpeg = Fiendish and Faithful MultiPurpose Encoding/decoding Glue
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