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, 14 insertions, 4 deletions

diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
index 5a225ffc44..5025fafdc5 100644
--- a/libavfilter/avfilter.h
+++ b/libavfilter/avfilter.h
@@ -71,8 +71,7 @@ typedef struct AVFilterFormats AVFilterFormats;
 typedef struct AVFilterChannelLayouts AVFilterChannelLayouts;
 
 /**
- * Get the number of elements in a NULL-terminated array of AVFilterPads (e.g.
- * AVFilter.inputs/outputs).
+ * Get the number of elements in an AVFilter's inputs or outputs array.
  */
 int avfilter_pad_count(const AVFilterPad *pads);
 
@@ -156,15 +155,16 @@ typedef struct AVFilter {
     const char *description;
 
     /**
-     * List of inputs, terminated by a zeroed element.
+     * List of static inputs.
      *
      * NULL if there are no (static) inputs. Instances of filters with
      * AVFILTER_FLAG_DYNAMIC_INPUTS set may have more inputs than present in
      * this list.
      */
     const AVFilterPad *inputs;
+
     /**
-     * List of outputs, terminated by a zeroed element.
+     * List of static outputs.
      *
      * NULL if there are no (static) outputs. Instances of filters with
      * AVFILTER_FLAG_DYNAMIC_OUTPUTS set may have more outputs than present in
@@ -196,6 +196,16 @@ typedef struct AVFilter {
      */
 
     /**
+     * The number of entries in the list of inputs.
+     */
+    uint16_t nb_inputs;
+
+    /**
+     * The number of entries in the list of outputs.
+     */
+    uint16_t nb_outputs;
+
+    /**
      * Filter pre-initialization function
      *
      * This callback will be called immediately after the filter context is