Add hermite resampler.

audio/hermite.c

@@ -0,0 +1,97 @@
+/*  SSNES - A Super Nintendo Entertainment System (SNES) Emulator frontend for libsnes.
+ *  Copyright (C) 2010-2011 - Hans-Kristian Arntzen
+ *
+ *  Some code herein may be based on code found in BSNES.
+ * 
+ *  SSNES is free software: you can redistribute it and/or modify it under the terms
+ *  of the GNU General Public License as published by the Free Software Found-
+ *  ation, either version 3 of the License, or (at your option) any later version.
+ *
+ *  SSNES is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ *  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ *  PURPOSE.  See the GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with SSNES.
+ *  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// Hermite resampler based on bsnes' audio library.
+
+#include "hermite.h"
+#include <stdlib.h>
+
+struct hermite_resampler
+{
+   float chan_data[2][4];
+   double r_frac;
+};
+
+static inline float hermite_kernel(float mu1, float a, float b, float c, float d)
+{
+   float mu2, mu3, m0, m1, a0, a1, a2, a3;
+
+   mu2 = mu1 * mu1;
+   mu3 = mu2 * mu1;
+
+   m0  = (c - a) * 0.5;
+   m1  = (d - b) * 0.5;
+
+   a0 = +2 * mu3 - 3 * mu2 + 1;
+   a1 =      mu3 - 2 * mu2 + mu1;
+   a2 =      mu3 -     mu2;
+   a3 = -2 * mu3 + 3 * mu2;
+
+   return (a0 * b) + (a1 * m0) + (a2 * m1) + (a3 * c);
+}
+
+hermite_resampler_t *hermite_new(void)
+{
+   hermite_resampler_t *re = calloc(1, sizeof(*re));
+   if (!re)
+      return NULL;
+   return re;
+}
+
+size_t hermite_process(hermite_resampler_t *re, const struct hermite_data *data)
+{
+   double r_step = 1.0 / data->ratio;
+   size_t processed = 0;
+
+   size_t in_frames = data->in_frames;
+   const float *in_data = data->in_data;
+   float *out_data = data->out_data;
+
+   while (in_frames > 0)
+   {
+      while (re->r_frac <= 1.0)
+      {
+         re->r_frac += r_step;
+         for (unsigned i = 0; i < 2; i++)
+         {
+            float res = hermite_kernel(re->r_frac, 
+                  re->chan_data[i][0], re->chan_data[i][1], re->chan_data[i][2], re->chan_data[i][3]);
+            *out_data++ = res;
+         }
+         processed++;
+      }
+
+      re->r_frac -= 1.0;
+
+      for (unsigned i = 0; i < 2; i++)
+      {
+         re->chan_data[i][0] = re->chan_data[i][1];
+         re->chan_data[i][1] = re->chan_data[i][2];
+         re->chan_data[i][2] = re->chan_data[i][3];
+         re->chan_data[i][3] = *in_data++;
+      }
+
+      in_frames--;
+   }
+   return processed;
+}
+
+void hermite_free(hermite_resampler_t *re)
+{
+   free(re);
+}
+

audio/hermite.h

@@ -0,0 +1,42 @@
+/*  SSNES - A Super Nintendo Entertainment System (SNES) Emulator frontend for libsnes.
+ *  Copyright (C) 2010-2011 - Hans-Kristian Arntzen
+ *
+ *  Some code herein may be based on code found in BSNES.
+ * 
+ *  SSNES is free software: you can redistribute it and/or modify it under the terms
+ *  of the GNU General Public License as published by the Free Software Found-
+ *  ation, either version 3 of the License, or (at your option) any later version.
+ *
+ *  SSNES is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ *  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ *  PURPOSE.  See the GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with SSNES.
+ *  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// Hermite resampler based on bsnes' audio library.
+
+#ifndef __SSNES_HERMITE_H
+#define __SSNES_HERMITE_H
+
+#include <stddef.h>
+
+typedef struct hermite_resampler hermite_resampler_t;
+
+hermite_resampler_t *hermite_new(void);
+
+struct hermite_data
+{
+   const float *in_data;
+   float *out_data; // We make it really simple and assume that there is always enough space. :)
+
+   size_t in_frames;
+   double ratio;
+};
+
+size_t hermite_process(hermite_resampler_t *re, const struct hermite_data *data);
+void hermite_free(hermite_resampler_t *re);
+
+#endif
+