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, 4 insertions, 8 deletions

diff --git a/libavfilter/f_realtime.c b/libavfilter/f_realtime.c
index 332ef21ac5..125bd6131c 100644
--- a/libavfilter/f_realtime.c
+++ b/libavfilter/f_realtime.c
@@ -81,7 +81,6 @@ static const AVFilterPad avfilter_vf_realtime_inputs[] = {
         .type         = AVMEDIA_TYPE_VIDEO,
         .filter_frame = filter_frame,
     },
-    { NULL }
 };
 
 static const AVFilterPad avfilter_vf_realtime_outputs[] = {
@@ -89,7 +88,6 @@ static const AVFilterPad avfilter_vf_realtime_outputs[] = {
         .name = "default",
         .type = AVMEDIA_TYPE_VIDEO,
     },
-    { NULL }
 };
 
 const AVFilter ff_vf_realtime = {
@@ -97,8 +95,8 @@ const AVFilter ff_vf_realtime = {
     .description = NULL_IF_CONFIG_SMALL("Slow down filtering to match realtime."),
     .priv_size   = sizeof(RealtimeContext),
     .priv_class  = &realtime_class,
-    .inputs      = avfilter_vf_realtime_inputs,
-    .outputs     = avfilter_vf_realtime_outputs,
+    FILTER_INPUTS(avfilter_vf_realtime_inputs),
+    FILTER_OUTPUTS(avfilter_vf_realtime_outputs),
 };
 #endif /* CONFIG_REALTIME_FILTER */
 
@@ -113,7 +111,6 @@ static const AVFilterPad arealtime_inputs[] = {
         .type         = AVMEDIA_TYPE_AUDIO,
         .filter_frame = filter_frame,
     },
-    { NULL }
 };
 
 static const AVFilterPad arealtime_outputs[] = {
@@ -121,7 +118,6 @@ static const AVFilterPad arealtime_outputs[] = {
         .name = "default",
         .type = AVMEDIA_TYPE_AUDIO,
     },
-    { NULL }
 };
 
 const AVFilter ff_af_arealtime = {
@@ -129,7 +125,7 @@ const AVFilter ff_af_arealtime = {
     .description = NULL_IF_CONFIG_SMALL("Slow down filtering to match realtime."),
     .priv_size   = sizeof(RealtimeContext),
     .priv_class  = &arealtime_class,
-    .inputs      = arealtime_inputs,
-    .outputs     = arealtime_outputs,
+    FILTER_INPUTS(arealtime_inputs),
+    FILTER_OUTPUTS(arealtime_outputs),
 };
 #endif /* CONFIG_AREALTIME_FILTER */