add method availableOutputBuffer()

The method availableOutputBuffer() calculates how many chunks are in
use.  This simplifies code which needs this information, and it can
run without knowing OutputBuffer internals.  The function knows how to
calculate this when begin>end; this might have been a bug in
decodeParent(), which does not.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7250 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/decode.c

@@ -425,8 +425,7 @@ static void decodeParent(PlayerControl * pc, DecoderControl * dc, OutputBuffer *
 	pc->play = 0;
 	wakeup_main_task();
 
-	while ((unsigned)cb->end - cb->begin < bbp &&
-	       cb->end != buffered_chunks - 1 &&
+	while (availableOutputBuffer(cb) < bbp &&
 	       dc->state != DECODE_STATE_STOP) {
 		processDecodeInput();
 		player_sleep();

src/outputBuffer.c

@@ -57,6 +57,14 @@ void flushOutputBuffer(OutputBuffer * cb)
 	}
 }
 
+unsigned availableOutputBuffer(const OutputBuffer * cb)
+{
+	if (cb->end >= cb->begin)
+		return cb->end - cb->begin;
+	else
+		return cb->end + buffered_chunks - cb->begin;
+}
+
 /**
  * Return the tail chunk has room for additional data.  If there is no
  * room in the queue, this function blocks until the player thread has

src/outputBuffer.h

@@ -55,6 +55,9 @@ void clearOutputBuffer(OutputBuffer * cb);
 
 void flushOutputBuffer(OutputBuffer * cb);
 
+/** determine the number of decoded chunks */
+unsigned availableOutputBuffer(const OutputBuffer * cb);
+
 /* we send inStream for buffering the inputStream while waiting to
    send the next chunk */
 int sendDataToOutputBuffer(OutputBuffer * cb,