libardour: * Add basic classes for later support of multiple interpolation algorithms for varispeed

                * Add unit tests: Test which shows how the varispeed implementation in diskstream is broken.

git-svn-id: svn://localhost/ardour2/branches/3.0@5144 d708f5d6-7413-0410-9779-e7cbd77b26cf

1 files changed, 43 insertions, 0 deletions

diff --git a/libs/ardour/interpolation.cc b/libs/ardour/interpolation.cc
new file mode 100644
index 0000000000..7aece6453c
--- /dev/null
+++ b/libs/ardour/interpolation.cc
@@ -0,0 +1,43 @@
+#include <stdint.h>
+#include "ardour/interpolation.h"
+
+nframes_t
+LinearInterpolation::interpolate (nframes_t nframes, Sample *input, Sample *output)
+{
+	// the idea behind phase 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
+	// so the "phase" element, if you want to think about this way, 
+	// varies from 0 to 1, representing the "offset" between samples
+	uint64_t    phase = last_phase;
+	
+	// acceleration
+	int64_t     phi_delta;
+
+	// phi = fixed point speed
+	if (phi != target_phi) {
+		phi_delta = ((int64_t)(target_phi - phi)) / nframes;
+	} else {
+		phi_delta = 0;
+	}
+	
+	// index in the input buffers
+	nframes_t   i = 0;
+
+	for (nframes_t outsample = 0; outsample < nframes; ++outsample) {
+		i = phase >> 24;
+		Sample fractional_phase_part = (phase & fractional_part_mask) / binary_scaling_factor;
+		
+        // Linearly interpolate into the output buffer
+        // using fixed point math
+		output[outsample] = 
+			input[i] * (1.0f - fractional_phase_part) +
+			input[i+1] * fractional_phase_part;
+		phase += phi + phi_delta;
+	}
+
+	last_phase = (phase & fractional_part_mask);
+	
+	// playback distance
+	return i;
+}