Add libs

3 files changed, 182 insertions, 0 deletions

diff --git a/src/libsamplerate/Makefile.am b/src/libsamplerate/Makefile.am
new file mode 100644
index 0000000..bd2319f
--- /dev/null
+++ b/src/libsamplerate/Makefile.am
@@ -0,0 +1,6 @@
+AM_CPPFLAGS = -Wall -Wextra -g $(all_includes)
+
+noinst_LIBRARIES = libsamplerate.a
+
+libsamplerate_a_SOURCES = \
+	samplerate.c
diff --git a/src/libsamplerate/samplerate.c b/src/libsamplerate/samplerate.c
new file mode 100644
index 0000000..7076366
--- /dev/null
+++ b/src/libsamplerate/samplerate.c
@@ -0,0 +1,157 @@
+/* Sample rate conversion
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * 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 <stdio.h>
+#include <stdint.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include "../libsample/sample.h"
+#include "samplerate.h"
+
+int init_samplerate(samplerate_t *state, double low_samplerate, double high_samplerate, double filter_cutoff)
+{
+	memset(state, 0, sizeof(*state));
+	state->factor = high_samplerate / low_samplerate;
+	if (state->factor < 1.0) {
+		fprintf(stderr, "Software error: Low sample rate must be lower than high sample rate, aborting!\n");
+		abort();
+	}
+
+	iir_lowpass_init(&state->up.lp, filter_cutoff, high_samplerate, 2);
+	iir_lowpass_init(&state->down.lp, filter_cutoff, high_samplerate, 2);
+
+	return 0;
+}
+
+/* convert high sample rate to low sample rate */
+int samplerate_downsample(samplerate_t *state, sample_t *samples, int input_num)
+{
+	int output_num = 0, i, idx;
+	double factor = state->factor, in_index, diff;
+	sample_t output[(int)((double)input_num / factor + 0.5) + 10]; /* add some safety */
+	sample_t last_sample;
+
+	/* filter down */
+	iir_process(&state->down.lp, samples, input_num);
+
+	/* get last sample for interpolation */
+	last_sample = state->down.last_sample;
+
+	/* resample filtered result */
+	in_index = state->down.in_index;
+
+	for (i = 0; ; i++) {
+		/* convert index to int */
+		idx = (int)in_index;
+		/* if index is outside input sample range, we are done */
+		if (idx >= input_num)
+			break;
+		/* linear interpolation */
+		diff = in_index - (double)idx;
+		if (idx)
+			output[i] = samples[idx - 1] * (1.0 - diff) + samples[idx] * diff;
+		else
+			output[i] = last_sample * (1.0 - diff) + samples[idx] * diff;
+		/* count output number */
+		output_num++;
+		/* increment input index */
+		in_index += factor;
+	}
+
+	/* store last sample for interpolation */
+	if (input_num)
+		state->down.last_sample = samples[input_num - 1];
+
+	/* remove number of input samples from index */
+	in_index -= (double)input_num;
+	/* in_index cannot be negative, except due to rounding error, so... */
+	if ((int)in_index < 0)
+		in_index = 0.0;
+
+	state->down.in_index = in_index;
+
+	/* copy samples */
+	for (i = 0; i < output_num; i++)
+		*samples++ = output[i];
+
+	return output_num;
+}
+
+/* convert low sample rate to high sample rate */
+int samplerate_upsample(samplerate_t *state, sample_t *input, int input_num, sample_t *output)
+{
+	int output_num = 0, i, idx;
+	double factor = 1.0 / state->factor, in_index, diff;
+	sample_t buff[(int)((double)input_num / factor + 0.5) + 10]; /* add some safety */
+	sample_t *samples, last_sample;
+
+	/* get last sample for interpolation */
+	last_sample = state->up.last_sample;
+
+	if (input == output)
+		samples = buff;
+	else
+		samples = output;
+
+	/* resample input */
+	in_index = state->up.in_index;
+
+	for (i = 0; ; i++) {
+		/* convert index to int */
+		idx = (int)in_index;
+		/* if index is outside input sample range, we are done */
+		if (idx >= input_num)
+			break;
+		/* linear interpolation */
+		diff = in_index - (double)idx;
+		if (idx)
+			samples[i] = input[idx - 1] * (1.0 - diff) + input[idx] * diff;
+		else
+			samples[i] = last_sample * (1.0 - diff) + input[idx] * diff;
+		/* count output number */
+		output_num++;
+		/* increment input index */
+		in_index += factor;
+	}
+
+	/* store last sample for interpolation */
+	if (input_num)
+		state->up.last_sample = input[input_num - 1];
+
+	/* remove number of input samples from index */
+	in_index -= (double)input_num;
+	/* in_index cannot be negative, except due to rounding error, so... */
+	if ((int)in_index < 0)
+		in_index = 0.0;
+
+	state->up.in_index = in_index;
+
+	/* filter up */
+	iir_process(&state->up.lp, samples, output_num);
+
+	if (input == output) {
+		/* copy samples */
+		for (i = 0; i < output_num; i++)
+			*output++ = samples[i];
+	}
+
+	return output_num;
+}
+
diff --git a/src/libsamplerate/samplerate.h b/src/libsamplerate/samplerate.h
new file mode 100644
index 0000000..8f8ea87
--- /dev/null
+++ b/src/libsamplerate/samplerate.h
@@ -0,0 +1,19 @@
+#include "../libfilter/iir_filter.h"
+
+typedef struct samplerate {
+	double factor;
+	struct {
+		iir_filter_t lp;
+		sample_t last_sample;
+		double in_index;
+	} down;
+	struct {
+		iir_filter_t lp;
+		sample_t last_sample;
+		double in_index;
+	} up;
+} samplerate_t;
+
+int init_samplerate(samplerate_t *state, double low_samplerate, double high_samplerate, double filter_cutoff);
+int samplerate_downsample(samplerate_t *state, sample_t *samples, int input_num);
+int samplerate_upsample(samplerate_t *state, sample_t *input, int input_num, sample_t *output);