3 files changed, 87 insertions, 14 deletions

diff --git a/libs/ardour/ardour/audio_diskstream.h b/libs/ardour/ardour/audio_diskstream.h
index 55cb747a4c..ecced007cf 100644
--- a/libs/ardour/ardour/audio_diskstream.h
+++ b/libs/ardour/ardour/audio_diskstream.h
@@ -146,7 +146,7 @@ class AudioDiskstream : public Diskstream
 		}
 	}
 	
-	LibSamplerateInterpolation interpolation;
+	FixedPointLinearInterpolation interpolation;
 
 	XMLNode* deprecated_io_node;
 	
diff --git a/libs/ardour/ardour/interpolation.h b/libs/ardour/ardour/interpolation.h
index cec951c841..deb0204794 100644
--- a/libs/ardour/ardour/interpolation.h
+++ b/libs/ardour/ardour/interpolation.h
@@ -8,18 +8,90 @@
 
 namespace ARDOUR {
 
-class LibSamplerateInterpolation {
-protected:
-	double   _speed;
-	
-	std::vector<SRC_STATE*>  state;
-	std::vector<SRC_DATA*>   data;
-	
-	int        error;
-	
-	void reset_state ();
+class Interpolation {
+ protected:
+         double   _speed, _target_speed;
+             
+ public:
+         Interpolation () { _speed = 1.0; }
+     
+         void set_speed (double new_speed)          { _speed = new_speed; }
+         void set_target_speed (double new_speed)   { _target_speed = new_speed; }
+
+         double target_speed()          const { return _target_speed; }
+         double speed()                 const { return _speed; }
+         
+         void add_channel_to (int input_buffer_size, int output_buffer_size) {}
+         void remove_channel_from () {}
+  
+         nframes_t interpolate (int channel, nframes_t nframes, Sample* input, Sample* output) {}
+         void reset () {}
+};
+
+// 40.24 fixpoint math
+#define FIXPOINT_ONE 0x1000000
+
+class FixedPointLinearInterpolation : public Interpolation {
+    protected:
+    /// speed in fixed point math
+    uint64_t      phi;
+    
+    /// target speed in fixed point math
+    uint64_t      target_phi;
+    
+    std::vector<uint64_t> last_phase;
+
+	// Fixed point is just an integer with an implied scaling factor. 
+	// In 40.24 the scaling factor is 2^24 = 16777216,  
+	// so a value of 10*2^24 (in integer space) is equivalent to 10.0. 
+	//
+	// The advantage is that addition and modulus [like x = (x + y) % 2^40]  
+	// have no rounding errors and no drift, and just require a single integer add.
+	// (swh)
 	
-public:
+	static const int64_t fractional_part_mask  = 0xFFFFFF;
+	static const Sample  binary_scaling_factor = 16777216.0f;
+    
+    public:
+    	FixedPointLinearInterpolation () : phi (FIXPOINT_ONE), target_phi (FIXPOINT_ONE) {}
+    
+        void set_speed (double new_speed) {
+            target_phi = (uint64_t) (FIXPOINT_ONE * fabs(new_speed));
+            phi = target_phi;
+        }
+        
+        void add_channel_to (int input_buffer_size, int output_buffer_size);
+        void remove_channel_from ();
+         
+        nframes_t interpolate (int channel, nframes_t nframes, Sample* input, Sample* output);
+        void reset ();
+};
+
+ class LinearInterpolation : public Interpolation {
+ protected:
+    // the idea is that when the speed is not 1.0, we have to 
+    // interpolate between samples and then we have to store where we thought we were. 
+    // rather than being at sample N or N+1, we were at N+0.8792922
+    std::vector<double> phase;
+    
+ public:
+         void add_channel_to (int input_buffer_size, int output_buffer_size);
+         void remove_channel_from ();
+     
+         nframes_t interpolate (int channel, nframes_t nframes, Sample* input, Sample* output);
+         void reset ();
+ };
+
+class LibSamplerateInterpolation : public Interpolation {
+ protected:
+    std::vector<SRC_STATE*>  state;
+    std::vector<SRC_DATA*>   data;
+    
+    int        error;
+    
+    void reset_state ();
+    
+ public:
         LibSamplerateInterpolation ();
         ~LibSamplerateInterpolation ();
     
@@ -31,8 +103,9 @@ public:
         void remove_channel_from (); 
  
         nframes_t interpolate (int channel, nframes_t nframes, Sample* input, Sample* output);
+        void reset() { reset_state (); }
 };
 
 } // namespace ARDOUR
 
-#endif
\ No newline at end of file
+#endif
diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index 8b291dd75b..1dd40affdb 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -1011,7 +1011,7 @@ class Session : public PBD::StatefulDestructible, public boost::noncopyable
 	volatile double             _transport_speed;
 	double                      _last_transport_speed;
 	double                      _target_transport_speed;
-	LibSamplerateInterpolation  interpolation;
+	FixedPointLinearInterpolation  interpolation;
 	
 	bool                     auto_play_legal;
 	nframes_t               _last_slave_transport_frame;