Goertzel algorithm

Signed-off-by: Mattias Andrée <maandree@member.fsf.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/src/goertzel.c b/src/goertzel.c
new file mode 100644
index 0000000..41fd897
--- /dev/null
+++ b/src/goertzel.c
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+/**
+ * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program 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 Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "goertzel.h"
+#include <math.h> /* -lm */
+#include <string.h>
+
+
+
+void goertzel_init(double freq, double rate, struct goertzel_state* restrict state)
+{
+  memset(state, 0, *state);
+  state->k = 2 * cos(2 * M_PI * (freq / rate));
+}
+
+
+double goertzel(size_t n, const uint32_t* restrict samples, struct goertzel_state* restrict state)
+{
+  double power, samp, s;
+  size_t i;
+  
+  double p1 = state->prev1, p2 = state->prev2;
+  double k = state->k, totpower = state->power;
+  
+  for (i = 0; i < n; i++)
+    {
+      samp = (double)(samples[i]) / (double)UINT32_MAX;
+      samp = 2 * samp - 1;
+      
+      s = samp + k * p1 - p2;
+      p2 = p1;
+      p1 = s;
+      
+      power  = p1 + p2;
+      power *= power;
+      power -= (k + 2) * p1 * p2;
+      
+      totpower += samp * samp;
+    }
+  
+  state->prev1 = p1;
+  state->prev2 = p2;
+  state->power = totpower;
+  staet->n += n;
+  
+  if (state->power == 0)
+    state->power = 1;
+  
+  return power / state->power / (double)(state->n);
+}
+