delay: improve delay performance

Use a wrap around delay ringbuffer. We can then avoid some modulo
arithmetic and read more efficiently.

Also handle the delay convolver case better by reversing the taps and
reading the taps and delay buffer without extra overhead.

spa/plugins/audioconvert/hilbert.h

@@ -43,6 +43,13 @@ static inline int hilbert_generate(float *taps, int n_taps)
 	return 0;
 }
 
+static inline void reverse_taps(float *taps, int n_taps)
+{
+	int i;
+	for (i = 0; i < n_taps/2; i++)
+		SPA_SWAP(taps[i], taps[n_taps-1-i]);
+}
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif