Move the polyphase resampler to the common lib

1 files changed, 45 insertions, 0 deletions

diff --git a/common/polyphase_resampler.h b/common/polyphase_resampler.h
new file mode 100644
index 00000000..e9833d12
--- /dev/null
+++ b/common/polyphase_resampler.h
@@ -0,0 +1,45 @@
+#ifndef POLYPHASE_RESAMPLER_H
+#define POLYPHASE_RESAMPLER_H
+
+#include <vector>
+
+
+/* This is a polyphase sinc-filtered resampler. It is built for very high
+ * quality results, rather than real-time performance.
+ *
+ *              Upsample                      Downsample
+ *
+ *              p/q = 3/2                     p/q = 3/5
+ *
+ *          M-+-+-+->                     M-+-+-+->
+ *         -------------------+          ---------------------+
+ *   p  s * f f f f|f|        |    p  s * f f f f f           |
+ *   |  0 *   0 0 0|0|0       |    |  0 *   0 0 0 0|0|        |
+ *   v  0 *     0 0|0|0 0     |    v  0 *     0 0 0|0|0       |
+ *      s *       f|f|f f f   |       s *       f f|f|f f     |
+ *      0 *        |0|0 0 0 0 |       0 *         0|0|0 0 0   |
+ *         --------+=+--------+       0 *          |0|0 0 0 0 |
+ *          d . d .|d|. d . d            ----------+=+--------+
+ *                                        d . . . .|d|. . . .
+ *          q->
+ *                                        q-+-+-+->
+ *
+ *   P_f(i,j) = q i mod p + pj
+ *   P_s(i,j) = floor(q i / p) - j
+ *   d[i=0..N-1] = sum_{j=0}^{floor((M - 1) / p)} {
+ *                   { f[P_f(i,j)] s[P_s(i,j)],  P_f(i,j) < M
+ *                   { 0,                        P_f(i,j) >= M. }
+ */
+
+struct PPhaseResampler {
+    using uint = unsigned int;
+
+    void init(const uint srcRate, const uint dstRate);
+    void process(const uint inN, const double *in, const uint outN, double *out);
+
+private:
+    uint mP, mQ, mM, mL;
+    std::vector<double> mF;
+};
+
+#endif /* POLYPHASE_RESAMPLER_H */