1 files changed, 74 insertions, 0 deletions
diff --git a/src/include/interpolate.h b/src/include/interpolate.h
new file mode 100644
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+++ b/src/include/interpolate.h
@@ -0,0 +1,74 @@
+#ifndef blop_interpolate_h
+#define blop_interpolate_h
+
+#include "blop_config.h"
+#include "math_func.h"
+
+/**
+   Interpolate between p0 and n0 taking the previous (p1) and next (n1) points
+   into account, using a 3rd order polynomial (a.k.a. cubic spline).
+   @param interval Normalised time interval between intepolated sample and p0
+   @param p1 Sample two previous to interpolated one
+   @param p0 Previous sample to interpolated one
+   @param n0 Sample following interpolated one
+   @param n1 Sample following n0
+   @return Interpolated sample.
+
+   Adapted from Steve Harris' plugin code
+   swh-plugins-0.2.7/ladspa-util.h::cube_interp
+   http://plugin.org.uk/releases/0.2.7/
+*/
+static inline float
+interpolate_cubic(float interval,
+                  float p1,
+                  float p0,
+                  float n0,
+                  float n1)
+{
+	return p0 + 0.5f * interval * (n0 - p1 +
+	                   interval * (4.0f * n0 + 2.0f * p1 - 5.0f * p0 - n1 +
+	                   interval * (3.0f * (p0 - n0) - p1 + n1)));
+}
+
+/**
+   Interpolate between p0 and n0 taking the previous (p1) and next (n1) points
+   into account, using a 5th order polynomial.
+   @param interval Normalised time interval between intepolated sample and p0
+   @param p1 Sample two previous to interpolated one
+   @param p0 Previous sample to interpolated one
+   @param n0 Sample following interpolated one
+   @param n1 Sample following n0
+   @return Interpolated sample.
+
+   Adapted from http://www.musicdsp.org/archive.php?classid=5#62
+*/
+static inline float
+interpolate_quintic(float interval,
+                    float p1,
+                    float p0,
+                    float n0,
+                    float n1)
+{
+	return p0 + 0.5f * interval * (n0 - p1 +
+	                   interval * (n0 - 2.0f * p0 + p1 +
+	                   interval * ( 9.0f * (n0 - p0) + 3.0f * (p1 - n1) +
+	                   interval * (15.0f * (p0 - n0) + 5.0f * (n1 - p1) +
+	                   interval * ( 6.0f * (n0 - p0) + 2.0f * (p1 - n1))))));
+}
+
+/**
+   Linear interpolation
+*/
+static inline float
+f_lerp (float value,
+        float v1,
+        float v2)
+{
+	value -= LRINTF (value - 0.5f);
+	value *= (v2 - v1);
+	value += v1;
+
+	return value;
+}
+
+#endif /* blop_interpolate_h */