avcodec/dcaenc: Simplify channel layout check

ff_encode_preinit() ensures that the channel layout is equivalent
to one of the channel layouts in AVCodec.ch_layout; given that
all of these channel layouts have distinct numbers of channels,
one can therefore uniquely determine the channel layout by
the number of channels.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/dcaenc.c

@@ -222,16 +222,25 @@ static int encode_init(AVCodecContext *avctx)
     if (ff_dcaadpcm_init(&c->adpcm_ctx))
         return AVERROR(ENOMEM);
 
-    if (!av_channel_layout_compare(&layout, &(AVChannelLayout)AV_CHANNEL_LAYOUT_MONO))
+    switch (layout.nb_channels) {
+    case 1: /* mono */
         c->channel_config = 0;
-    else if (!av_channel_layout_compare(&layout, &(AVChannelLayout)AV_CHANNEL_LAYOUT_STEREO))
+        break;
+    case 2: /* stereo */
         c->channel_config = 2;
-    else if (!av_channel_layout_compare(&layout, &(AVChannelLayout)AV_CHANNEL_LAYOUT_2_2))
+        break;
+    case 4: /* 2.2 */
         c->channel_config = 8;
-    else if (!av_channel_layout_compare(&layout, &(AVChannelLayout)AV_CHANNEL_LAYOUT_5POINT0))
+        break;
+    case 5: /* 5.0 */
         c->channel_config = 9;
-    else if (!av_channel_layout_compare(&layout, &(AVChannelLayout)AV_CHANNEL_LAYOUT_5POINT1))
+        break;
+    case 6: /* 5.1 */
         c->channel_config = 9;
+        break;
+    default:
+        av_assert1(!"impossible channel layout");
+    }
 
     if (c->lfe_channel) {
         c->fullband_channels--;