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/af_sidechaincompress.c b/libavfilter/af_sidechaincompress.c
index 8e8547c3a4..c964e0d27c 100644
--- a/libavfilter/af_sidechaincompress.c
+++ b/libavfilter/af_sidechaincompress.c
@@ -371,7 +371,6 @@ static const AVFilterPad sidechaincompress_inputs[] = {
         .name           = "sidechain",
         .type           = AVMEDIA_TYPE_AUDIO,
     },
-    { NULL }
 };
 
 static const AVFilterPad sidechaincompress_outputs[] = {
@@ -380,7 +379,6 @@ static const AVFilterPad sidechaincompress_outputs[] = {
         .type          = AVMEDIA_TYPE_AUDIO,
         .config_props  = config_output,
     },
-    { NULL }
 };
 
 const AVFilter ff_af_sidechaincompress = {
@@ -391,8 +389,8 @@ const AVFilter ff_af_sidechaincompress = {
     .query_formats  = query_formats,
     .activate       = activate,
     .uninit         = uninit,
-    .inputs         = sidechaincompress_inputs,
-    .outputs        = sidechaincompress_outputs,
+    FILTER_INPUTS(sidechaincompress_inputs),
+    FILTER_OUTPUTS(sidechaincompress_outputs),
     .process_command = process_command,
 };
 #endif  /* CONFIG_SIDECHAINCOMPRESS_FILTER */
@@ -454,7 +452,6 @@ static const AVFilterPad acompressor_inputs[] = {
         .type           = AVMEDIA_TYPE_AUDIO,
         .filter_frame   = acompressor_filter_frame,
     },
-    { NULL }
 };
 
 static const AVFilterPad acompressor_outputs[] = {
@@ -463,7 +460,6 @@ static const AVFilterPad acompressor_outputs[] = {
         .type          = AVMEDIA_TYPE_AUDIO,
         .config_props  = compressor_config_output,
     },
-    { NULL }
 };
 
 const AVFilter ff_af_acompressor = {
@@ -472,8 +468,8 @@ const AVFilter ff_af_acompressor = {
     .priv_size      = sizeof(SidechainCompressContext),
     .priv_class     = &acompressor_class,
     .query_formats  = acompressor_query_formats,
-    .inputs         = acompressor_inputs,
-    .outputs        = acompressor_outputs,
+    FILTER_INPUTS(acompressor_inputs),
+    FILTER_OUTPUTS(acompressor_outputs),
     .process_command = process_command,
 };
 #endif  /* CONFIG_ACOMPRESSOR_FILTER */