added outputBufferRelative()

The cross-fade check is still very complicated whenever it uses
OutputBuffer internals.  Greatly simplify another check by introducing
outputBufferRelative().

git-svn-id: https://svn.musicpd.org/mpd/trunk@7264 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/decode.c

@@ -496,12 +496,8 @@ static void decodeParent(PlayerControl * pc, DecoderControl * dc, OutputBuffer *
 		else if (!outputBufferEmpty(cb) && cb->begin != next) {
 			unsigned int fadePosition;
 			if (doCrossFade == 1 && next >= 0 &&
-			    ((next > cb->begin &&
-			      (fadePosition = next - cb->begin)
-			      <= crossFadeChunks) ||
-			     (cb->begin > next &&
-			      (fadePosition = next - cb->begin +
-			       buffered_chunks) <= crossFadeChunks))) {
+			    (fadePosition = outputBufferRelative(cb, next))
+			    <= crossFadeChunks) {
 				/* perform cross fade */
 				if (nextChunk < 0) {
 					/* beginning of the cross fade

src/outputBuffer.c

@@ -62,12 +62,17 @@ int outputBufferEmpty(const OutputBuffer * cb)
 	return cb->begin == cb->end;
 }
 
+unsigned int outputBufferRelative(const OutputBuffer * cb, unsigned i)
+{
+	if (i >= cb->begin)
+		return i - cb->begin;
+	else
+		return i + buffered_chunks - cb->begin;
+}
+
 unsigned availableOutputBuffer(const OutputBuffer * cb)
 {
-	if (cb->end >= cb->begin)
-		return cb->end - cb->begin;
-	else
-		return cb->end + buffered_chunks - cb->begin;
+	return outputBufferRelative(cb, cb->end);
 }
 
 int outputBufferAbsolute(const OutputBuffer * cb, unsigned relative)

src/outputBuffer.h

@@ -58,6 +58,12 @@ void flushOutputBuffer(OutputBuffer * cb);
 /** is the buffer empty? */
 int outputBufferEmpty(const OutputBuffer * cb);
 
+/**
+ * what is the position of the specified chunk number, relative to
+ * the first chunk in use?
+ */
+unsigned int outputBufferRelative(const OutputBuffer * cb, unsigned i);
+
 /** determine the number of decoded chunks */
 unsigned availableOutputBuffer(const OutputBuffer * cb);