audio-channels: map buffer read-write only if channels differ

gst_audio_buffer_reorder_channels() was always mapping the buffer read-write
regardless whether any reordering was needed.  If the from and to channel order
is identical return immediately without remapping the buffer.

Add a small helper function gst_audio_channel_positions_equal() which is used
in both gst_audio_reorder_channels() and gst_audio_buffer_reorder_channels().

https://bugzilla.gnome.org/show_bug.cgi?id=773833

diff --git a/gst-libs/gst/audio/audio-channels.c b/gst-libs/gst/audio/audio-channels.c
index 5ce2f5c747d3c9a05d49c2ca4c76b602a9995159..77bbccf57c94787621a0f15206f92258fe17f51f 100644 (file)
--- a/gst-libs/gst/audio/audio-channels.c
+++ b/gst-libs/gst/audio/audio-channels.c
@@ -121,6 +121,19 @@ static const GstAudioChannelPosition default_channel_order[64] = {
   GST_AUDIO_CHANNEL_POSITION_INVALID
 };
 
+/*
+ * Compares @channels audio channel positions @p1 and @p2 if they are equal.
+ * In other words, tells whether channel reordering is needed (unequal) or not (equal).
+ *
+ * Returns: %TRUE if the channel positions are equal, i.e. no reordering is needed.
+ */
+static gboolean
+gst_audio_channel_positions_equal (const GstAudioChannelPosition * p1,
+    const GstAudioChannelPosition * p2, gint channels)
+{
+  return memcmp (p1, p2, channels * sizeof (p1[0])) == 0;
+}
+
 static gboolean
 check_valid_channel_positions (const GstAudioChannelPosition * position,
     gint channels, gboolean enforce_order, guint64 * channel_mask_out)
@@ -211,7 +224,7 @@ gst_audio_reorder_channels (gpointer data, gsize size, GstAudioFormat format,
   if (size == 0)
     return TRUE;
 
-  if (memcmp (from, to, channels * sizeof (from[0])) == 0)
+  if (gst_audio_channel_positions_equal (from, to, channels))
     return TRUE;
 
   if (!gst_audio_get_channel_reorder_map (channels, from, to, reorder_map))
@@ -260,6 +273,9 @@ gst_audio_buffer_reorder_channels (GstBuffer * buffer,
   g_return_val_if_fail (GST_IS_BUFFER (buffer), FALSE);
   g_return_val_if_fail (gst_buffer_is_writable (buffer), FALSE);
 
+  if (gst_audio_channel_positions_equal (from, to, channels))
+    return TRUE;
+
   gst_buffer_map (buffer, &info, GST_MAP_READWRITE);
 
   ret =