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-rw-r--r--src/goertzel.c64
-rw-r--r--src/goertzel.h34
2 files changed, 98 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
@@ -0,0 +1,64 @@
+/**
+ * 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);
+}
+
diff --git a/src/goertzel.h b/src/goertzel.h
new file mode 100644
index 0000000..ad1e4b8
--- /dev/null
+++ b/src/goertzel.h
@@ -0,0 +1,34 @@
+/**
+ * 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 <stddef.h>
+#include <stdint.h>
+
+
+
+struct goertzel_state
+{
+ double prev1;
+ double prev2;
+ double power;
+ size_t n;
+ double k;
+};
+
+
+void goertzel_init(double freq, double rate, struct goertzel_state* restrict state);
+double goertzel(size_t n, const uint32_t* restrict samples, struct goertzel_state* restrict state);
+