decoder/flac: move position code to FlacDecoder::GetDeltaPosition()

src/decoder/plugins/FlacCommon.cxx

@@ -151,6 +151,24 @@ flac_got_first_frame(FlacDecoder *data, const FLAC__FrameHeader *header)
 				0);
 }
 
+FLAC__uint64
+FlacDecoder::GetDeltaPosition(const FLAC__StreamDecoder &sd)
+{
+	FLAC__uint64 nbytes;
+	if (!FLAC__stream_decoder_get_decode_position(&sd, &nbytes))
+		return 0;
+
+	if (position > 0 && nbytes > position) {
+		nbytes -= position;
+		position += nbytes;
+	} else {
+		position = nbytes;
+		nbytes = 0;
+	}
+
+	return nbytes;
+}
+
 FLAC__StreamDecoderWriteStatus
 flac_common_write(FlacDecoder *data, const FLAC__Frame * frame,
 		  const FLAC__int32 *const buf[],

src/decoder/plugins/FlacCommon.hxx

@@ -69,6 +69,12 @@ struct FlacDecoder : public FlacInput {
 	 */
 	bool Initialize(unsigned sample_rate, unsigned bits_per_sample,
 			unsigned channels, FLAC__uint64 total_frames);
+
+	/**
+	 * Calculate the delta (in bytes) between the last frame and
+	 * the current frame.
+	 */
+	FLAC__uint64 GetDeltaPosition(const FLAC__StreamDecoder &sd);
 };
 
 void flac_metadata_common_cb(const FLAC__StreamMetadata * block,

src/decoder/plugins/FlacDecoderPlugin.cxx

@@ -65,20 +65,9 @@ flac_write_cb(const FLAC__StreamDecoder *dec, const FLAC__Frame *frame,
 	      const FLAC__int32 *const buf[], void *vdata)
 {
 	FlacDecoder *data = (FlacDecoder *) vdata;
-	FLAC__uint64 nbytes = 0;
-
-	if (FLAC__stream_decoder_get_decode_position(dec, &nbytes)) {
-		if (data->position > 0 && nbytes > data->position) {
-			nbytes -= data->position;
-			data->position += nbytes;
-		} else {
-			data->position = nbytes;
-			nbytes = 0;
-		}
-	} else
-		nbytes = 0;
 
-	return flac_common_write(data, frame, buf, nbytes);
+	return flac_common_write(data, frame, buf,
+				 data->GetDeltaPosition(*dec));
 }
 
 static bool