chore(fmod): add files from Chensne/DragonNest

lib/freeverb/allpass.h

@@ -0,0 +1,48 @@
+// Allpass filter declaration
+//
+// Written by Jezar at Dreampoint, June 2000
+// http://www.dreampoint.co.uk
+// This code is public domain
+
+#ifndef _allpass_
+#define _allpass_
+#include "denormals.h"
+
+class allpass
+{
+public:
+					allpass();
+			void	setbuffer(float *buf, int size);
+	inline  float	process(float inp);
+			void	mute();
+			void	setfeedback(float val);
+			float	getfeedback();
+// private:
+	float	feedback;
+	float	*buffer;
+	int		bufsize;
+	int		bufidx;
+};
+
+
+// Big to inline - but crucial for speed
+
+inline float allpass::process(float input)
+{
+	float output;
+	float bufout;
+	
+	bufout = buffer[bufidx];
+	undenormalise(bufout);
+	
+	output = -input + bufout;
+	buffer[bufidx] = input + (bufout*feedback);
+
+	if(++bufidx>=bufsize) bufidx = 0;
+
+	return output;
+}
+
+#endif//_allpass
+
+//ends