new bw_sr_reduce module (untested)

include/bw_sr_reduce.h

@@ -0,0 +1,150 @@
+/*
+ * Brickworks
+ *
+ * Copyright (C) 2022 Orastron Srl unipersonale
+ *
+ * Brickworks 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, version 3 of the License.
+ *
+ * Brickworks 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 Brickworks.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * File author: Stefano D'Angelo
+ */
+
+/*!
+ *  module_type {{{ dsp }}}
+ *  version {{{ 0.3.0 }}}
+ *  requires {{{ bw_config bw_common bw_math }}}
+ *  description {{{
+ *    Sample rate reducer.
+ *
+ *    This is purely an audio effect, it doesn't actually produce an output
+ *    signal at a lower sample rate. The algorithm is deliberately crude to
+ *    obtain the characteristic aliasing due to lo-fi downsampling.
+ *  }}}
+ *  changelog {{{
+ *    <ul>
+ *      <li>Version <strong>0.3.0</strong>:
+ *        <ul>
+ *          <li>First release.</li>
+ *        </ul>
+ *      </li>
+ *    </ul>
+ *  }}}
+ */
+
+#ifndef _BW_REDUCER_H
+#define _BW_REDUCER_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <bw_common.h>
+
+/*! api {{{
+ *    #### bw_sr_reduce_coeffs
+ *  ```>>> */
+typedef struct _bw_sr_reduce_coeffs bw_sr_reduce_coeffs;
+/*! <<<```
+ *    Coefficients and related.
+ *
+ *    #### bw_sr_reduce_state
+ *  ```>>> */
+typedef struct _bw_sr_reduce_state bw_sr_reduce_state;
+/*! <<<```
+ *    Internal state and related.
+ *
+ *    #### bw_sr_reduce_init()
+ *  ```>>> */
+static inline void bw_sr_reduce_init(bw_sr_reduce_coeffs *BW_RESTRICT coeffs);
+/*! <<<```
+ *    Initializes input parameter values in `coeffs`.
+ *
+ *    #### bw_sr_reduce_reset_state()
+ *  ```>>> */
+static inline void bw_sr_reduce_reset_state(const bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state);
+/*! <<<```
+ *    Resets the given `state` to its initial values using the given `coeffs`.
+ *
+ *    #### bw_sr_reduce_process1()
+ *  ```>>> */
+static inline float bw_sr_reduce_process1(const bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state, float x);
+/*! <<<```
+ *    Processes one input sample `x` using `coeffs`, while using and updating
+ *    `state`. Returns the corresponding output sample.
+ *
+ *    #### bw_sr_reduce_process()
+ *  ```>>> */
+static inline void bw_sr_reduce_process(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state, const float *x, float* y, int n_samples);
+/*! <<<```
+ *    Processes the first `n_samples` of the input buffer `x` and fills the
+ *    first `n_samples` of the output buffer `y`, while using and updating both
+ *    `coeffs` and `state` (control and audio rate).
+ *
+ *    #### bw_sr_reduce_set_ratio()
+ *  ```>>> */
+static inline void bw_sr_reduce_set_ratio(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, float value);
+/*! <<<```
+ *    Sets the output to input sample rate ratio in `coeffs`.
+ *
+ *    Valid input range: [`0.f`, `1.f`].
+ *
+ *    Default value: `1.f`.
+ *  }}} */
+
+/*** Implementation ***/
+
+/* WARNING: This part of the file is not part of the public API. Its content may
+ * change at any time in future versions. Please, do not use it directly. */
+
+#include <bw_math.h>
+
+struct _bw_sr_reduce_coeffs {
+	// Parameters
+	float	ratio;
+};
+
+struct _bw_sr_reduce_state {
+	float	phase;
+	float	y_z1;
+};
+
+static inline void bw_sr_reduce_init(bw_sr_reduce_coeffs *BW_RESTRICT coeffs) {
+	coeffs->ratio = 1.f;
+}
+
+static inline void bw_sr_reduce_reset_state(const bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state) {
+	state->phase = 1.f;
+}
+
+static inline float bw_sr_reduce_process1(const bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state, float x) {
+	state->phase += coeffs->ratio;
+	if (state->phase >= 1.f) {
+		state->y_z1 = x;
+		state->phase -= bw_floorf(state->phase);
+	}
+	return state->y_z1;
+}
+
+static inline void bw_sr_reduce_process(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state, const float *x, float* y, int n_samples) {
+	for (int i = 0; i < n_samples; i++)
+		y[i] = bw_sr_reduce_process1_scaling(coeffs, state, x[i]);
+}
+
+static inline void bw_sr_reduce_set_ratio(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, float value) {
+	coeffs->ratio = value;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif