avfilter/avfilter: Add numbers of (in|out)pads directly to AVFilter

Up until now, an AVFilter's lists of input and output AVFilterPads
were terminated by a sentinel and the only way to get the length
of these lists was by using avfilter_pad_count(). This has two
drawbacks: first, sizeof(AVFilterPad) is not negligible
(i.e. 64B on 64bit systems); second, getting the size involves
a function call instead of just reading the data.

This commit therefore changes this. The sentinels are removed and new
private fields nb_inputs and nb_outputs are added to AVFilter that
contain the number of elements of the respective AVFilterPad array.

Given that AVFilter.(in|out)puts are the only arrays of zero-terminated
AVFilterPads an API user has access to (AVFilterContext.(in|out)put_pads
are not zero-terminated and they already have a size field) the argument
to avfilter_pad_count() is always one of these lists, so it just has to
find the filter the list belongs to and read said number. This is slower
than before, but a replacement function that just reads the internal numbers
that users are expected to switch to will be added soon; and furthermore,
avfilter_pad_count() is probably never called in hot loops anyway.

This saves about 49KiB from the binary; notice that these sentinels are
not in .bss despite being zeroed: they are in .data.rel.ro due to the
non-sentinels.

Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/libavfilter/internal.h b/libavfilter/internal.h
index a0aa32af4d..51b0afa24d 100644
--- a/libavfilter/internal.h
+++ b/libavfilter/internal.h
@@ -141,6 +141,12 @@ static av_always_inline int ff_filter_execute(AVFilterContext *ctx, avfilter_act
     return ctx->internal->execute(ctx, func, arg, ret, nb_jobs);
 }
 
+#define FILTER_INOUTPADS(inout, array) \
+       .inout        = array, \
+       .nb_ ## inout = FF_ARRAY_ELEMS(array)
+#define FILTER_INPUTS(array) FILTER_INOUTPADS(inputs, (array))
+#define FILTER_OUTPUTS(array) FILTER_INOUTPADS(outputs, (array))
+
 /**
  * Tell if an integer is contained in the provided -1-terminated list of integers.
  * This is useful for determining (for instance) if an AVPixelFormat is in an