brickworks/include/bw_drive.h

/*
 * Brickworks
 *
 * Copyright (C) 2023, 2024 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 {{{ 1.1.1 }}}
 *  requires {{{
 *    bw_common bw_gain bw_hs1 bw_lp1 bw_math bw_mm2 bw_one_pole bw_peak
 *    bw_satur bw_svf
 *  }}}
 *  description {{{
 *    Overdrive effect.
 *
 *    Loosely inspired to the green "screaming" overdrive pedal.
 *  }}}
 *  changelog {{{
 *    <ul>
 *      <li>Version <strong>1.1.1</strong>:
 *        <ul>
 *          <li>Added debugging check in <code>bw_drive_process_multi()</code>
 *              to ensure that buffers used for both input and output appear at
 *              the same channel indices.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>1.1.0</strong>:
 *        <ul>
 *          <li>Now using <code>BW_NULL</code> and
 *              <code>BW_CXX_NO_ARRAY</code>.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>1.0.0</strong>:
 *        <ul>
 *          <li>Improved algorithm to be a bit more faithful to the
 *              original.</li>
 *          <li>Added initial input value to
 *              <code>bw_drive_reset_state()</code>.</li>
 *          <li>Added <code>bw_drive_reset_state_multi()</code> and updated C++
 *              API in this regard.</li>
 *          <li>Now <code>bw_drive_reset_state()</code> returns the initial
 *              output value.</li>
 *          <li>Added overloaded C++ <code>reset()</code> functions taking
 *              arrays as arguments.</li>
 *          <li><code>bw_drive_process()</code> and
 *              <code>bw_drive_process_multi()</code> now use
 *              <code>size_t</code> to count samples and channels.</li>
 *          <li>Added more <code>const</code> and <code>BW_RESTRICT</code>
 *              specifiers to input arguments and implementation.</li>
 *          <li>Moved C++ code to C header.</li>
 *          <li>Added overloaded C++ <code>process()</code> function taking
 *              C-style arrays as arguments.</li>
 *          <li>Removed usage of reserved identifiers.</li>
 *          <li>Clearly specified parameter validity ranges.</li>
 *          <li>Added debugging code.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>0.6.0</strong>:
 *        <ul>
 *          <li>Removed dependency on bw_config.</li>
 *        </ul>
 *      </li>
 *      <li>Version <strong>0.5.0</strong>:
 *        <ul>
 *          <li>First release.</li>
 *        </ul>
 *      </li>
 *    </ul>
 *  }}}
 */

#ifndef BW_DRIVE_H
#define BW_DRIVE_H

#include <bw_common.h>

#ifdef __cplusplus
extern "C" {
#endif

/*! api {{{
 *    #### bw_drive_coeffs
 *  ```>>> */
typedef struct bw_drive_coeffs bw_drive_coeffs;
/*! <<<```
 *    Coefficients and related.
 *
 *    #### bw_drive_state
 *  ```>>> */
typedef struct bw_drive_state bw_drive_state;
/*! <<<```
 *    Internal state and related.
 *
 *    #### bw_drive_init()
 *  ```>>> */
static inline void bw_drive_init(
	bw_drive_coeffs * BW_RESTRICT coeffs);
/*! <<<```
 *    Initializes input parameter values in `coeffs`.
 *
 *    #### bw_drive_set_sample_rate()
 *  ```>>> */
static inline void bw_drive_set_sample_rate(
	bw_drive_coeffs * BW_RESTRICT coeffs,
	float                         sample_rate);
/*! <<<```
 *    Sets the `sample_rate` (Hz) value in `coeffs`.
 *
 *    #### bw_drive_reset_coeffs()
 *  ```>>> */
static inline void bw_drive_reset_coeffs(
	bw_drive_coeffs * BW_RESTRICT coeffs);
/*! <<<```
 *    Resets coefficients in `coeffs` to assume their target values.
 *
 *    #### bw_drive_reset_state()
 *  ```>>> */
static inline float bw_drive_reset_state(
	const bw_drive_coeffs * BW_RESTRICT coeffs,
	bw_drive_state * BW_RESTRICT        state,
	float                               x_0);
/*! <<<```
 *    Resets the given `state` to its initial values using the given `coeffs`
 *    and the initial input value `x_0`.
 *
 *    Returns the corresponding initial output value.
 *
 *    #### bw_drive_reset_state_multi()
 *  ```>>> */
static inline void bw_drive_reset_state_multi(
	const bw_drive_coeffs * BW_RESTRICT              coeffs,
	bw_drive_state * BW_RESTRICT const * BW_RESTRICT state,
	const float *                                   x_0,
	float *                                         y_0,
	size_t                                          n_channels);
/*! <<<```
 *    Resets each of the `n_channels` `state`s to its initial values using the
 *    given `coeffs` and the corresponding initial input value in the `x_0`
 *    array.
 *
 *    The corresponding initial output values are written into the `y_0` array,
 *    if not `BW_NULL`.
 *
 *    #### bw_drive_update_coeffs_ctrl()
 *  ```>>> */
static inline void bw_drive_update_coeffs_ctrl(
	bw_drive_coeffs * BW_RESTRICT coeffs);
/*! <<<```
 *    Triggers control-rate update of coefficients in `coeffs`.
 *
 *    #### bw_drive_update_coeffs_audio()
 *  ```>>> */
static inline void bw_drive_update_coeffs_audio(
	bw_drive_coeffs * BW_RESTRICT coeffs);
/*! <<<```
 *    Triggers audio-rate update of coefficients in `coeffs`.
 *
 *    #### bw_drive_process1()
 *  ```>>> */
static inline float bw_drive_process1(
	const bw_drive_coeffs * BW_RESTRICT coeffs,
	bw_drive_state * BW_RESTRICT        state,
	float                               x);
/*! <<<```
 *    Processes one input sample `x` using `coeffs`, while using and updating
 *    `state`. Returns the corresponding output sample.
 *
 *    #### bw_drive_process()
 *  ```>>> */
static inline void bw_drive_process(
	bw_drive_coeffs * BW_RESTRICT coeffs,
	bw_drive_state * BW_RESTRICT  state,
	const float *                 x,
	float *                       y,
	size_t                        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_drive_process_multi()
 *  ```>>> */
static inline void bw_drive_process_multi(
	bw_drive_coeffs * BW_RESTRICT                    coeffs,
	bw_drive_state * BW_RESTRICT const * BW_RESTRICT state,
	const float * const *                            x,
	float * const *                                  y,
	size_t                                           n_channels,
	size_t                                           n_samples);
/*! <<<```
 *    Processes the first `n_samples` of the `n_channels` input buffers `x` and
 *    fills the first `n_samples` of the `n_channels` output buffers `y`, while
 *    using and updating both the common `coeffs` and each of the `n_channels`
 *    `state`s (control and audio rate).
 *
 *    #### bw_drive_set_drive()
 *  ```>>> */
static inline void bw_drive_set_drive(
	bw_drive_coeffs * BW_RESTRICT coeffs,
	float value);
/*! <<<```
 *    Sets the overdrive (input gain, approximately) to the given `value` in
 *    `coeffs`.
 *
 *    Valid range: [`0.f` (low overdrive), `1.f` (high overdrive)].
 *
 *    Default value: `0.f`.
 *
 *    #### bw_drive_set_tone()
 *  ```>>> */
static inline void bw_drive_set_tone(
	bw_drive_coeffs * BW_RESTRICT coeffs,
	float value);
/*! <<<```
 *    Sets the tone (filter) to the given `value` in `coeffs`.
 *
 *    Valid range: [`0.f` (low cutoff), `1.f` (high cutoff)].
 *
 *    Default value: `0.5f`.
 *
 *    #### bw_drive_set_volume()
 *  ```>>> */
static inline void bw_drive_set_volume(
	bw_drive_coeffs * BW_RESTRICT coeffs,
	float value);
/*! <<<```
 *    Sets the volume (output gain) to the given `value` in `coeffs`.
 *
 *    Valid range: [`0.f` (silence), `1.f` (max volume)].
 *
 *    Default value: `1.f`.
 *
 *    #### bw_drive_coeffs_is_valid()
 *  ```>>> */
static inline char bw_drive_coeffs_is_valid(
	const bw_drive_coeffs * BW_RESTRICT coeffs);
/*! <<<```
 *    Tries to determine whether `coeffs` is valid and returns non-`0` if it
 *    seems to be the case and `0` if it is certainly not. False positives are
 *    possible, false negatives are not.
 *
 *    `coeffs` must at least point to a readable memory block of size greater
 *    than or equal to that of `bw_drive_coeffs`.
 *
 *    #### bw_drive_state_is_valid()
 *  ```>>> */
static inline char bw_drive_state_is_valid(
	const bw_drive_coeffs * BW_RESTRICT coeffs,
	const bw_drive_state * BW_RESTRICT  state);
/*! <<<```
 *    Tries to determine whether `state` is valid and returns non-`0` if it
 *    seems to be the case and `0` if it is certainly not. False positives are
 *    possible, false negatives are not.
 *
 *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
 *    (`state` is supposed to be associated to `coeffs`).
 *
 *    `state` must at least point to a readable memory block of size greater
 *    than or equal to that of `bw_drive_state`.
 *  }}} */

#ifdef __cplusplus
}
#endif

/*** 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_svf.h>
#include <bw_hs1.h>
#include <bw_peak.h>
#include <bw_satur.h>
#include <bw_lp1.h>
#include <bw_gain.h>

#ifdef __cplusplus
extern "C" {
#endif

#ifdef BW_DEBUG_DEEP
enum bw_drive_coeffs_state {
	bw_drive_coeffs_state_invalid,
	bw_drive_coeffs_state_init,
	bw_drive_coeffs_state_set_sample_rate,
	bw_drive_coeffs_state_reset_coeffs
};
#endif

struct bw_drive_coeffs {
#ifdef BW_DEBUG_DEEP
	uint32_t			hash;
	enum bw_drive_coeffs_state	state;
	uint32_t			reset_id;
#endif

	// Sub-components
	bw_svf_coeffs			hp2_coeffs;
	bw_hs1_coeffs			hs1_coeffs;
	bw_peak_coeffs			peak_coeffs;
	bw_satur_coeffs			satur_coeffs;
	bw_lp1_coeffs			lp1_coeffs;
	bw_gain_coeffs			gain_coeffs;
};

struct bw_drive_state {
#ifdef BW_DEBUG_DEEP
	uint32_t	hash;
	uint32_t	coeffs_reset_id;
#endif

	// Sub-components
	bw_svf_state	hp2_state;
	bw_hs1_state	hs1_state;
	bw_peak_state	peak_state;
	bw_satur_state	satur_state;
	bw_lp1_state	lp1_state;
};

static inline void bw_drive_init(
		bw_drive_coeffs * BW_RESTRICT coeffs) {
	BW_ASSERT(coeffs != BW_NULL);

	bw_svf_init(&coeffs->hp2_coeffs);
	bw_hs1_init(&coeffs->hs1_coeffs);
	bw_peak_init(&coeffs->peak_coeffs);
	bw_satur_init(&coeffs->satur_coeffs);
	bw_lp1_init(&coeffs->lp1_coeffs);
	bw_gain_init(&coeffs->gain_coeffs);
	bw_svf_set_cutoff(&coeffs->hp2_coeffs, 16.f);
	bw_hs1_set_cutoff(&coeffs->hs1_coeffs, 200.f);
	bw_hs1_set_high_gain_dB(&coeffs->hs1_coeffs, 20.f);
	bw_peak_set_peak_gain_dB(&coeffs->peak_coeffs, 0.f);
	bw_peak_set_cutoff(&coeffs->peak_coeffs, 500.f);
	bw_peak_set_bandwidth(&coeffs->peak_coeffs, 9.5f);
	bw_satur_set_gain(&coeffs->satur_coeffs, 1.5f);
	bw_satur_set_gain_compensation(&coeffs->satur_coeffs, 1);
	bw_lp1_set_cutoff(&coeffs->lp1_coeffs, 400.f + (5e3f - 400.f) * 0.125f);

#ifdef BW_DEBUG_DEEP
	coeffs->hash = bw_hash_sdbm("bw_drive_coeffs");
	coeffs->state = bw_drive_coeffs_state_init;
	coeffs->reset_id = coeffs->hash + 1;
#endif
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state == bw_drive_coeffs_state_init);
}

static inline void bw_drive_set_sample_rate(
		bw_drive_coeffs * BW_RESTRICT coeffs,
		float                         sample_rate) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);

	bw_svf_set_sample_rate(&coeffs->hp2_coeffs, sample_rate);
	bw_hs1_set_sample_rate(&coeffs->hs1_coeffs, sample_rate);
	bw_peak_set_sample_rate(&coeffs->peak_coeffs, sample_rate);
	bw_satur_set_sample_rate(&coeffs->satur_coeffs, sample_rate);
	bw_lp1_set_sample_rate(&coeffs->lp1_coeffs, sample_rate);
	bw_gain_set_sample_rate(&coeffs->gain_coeffs, sample_rate);
	bw_svf_reset_coeffs(&coeffs->hp2_coeffs);
	bw_hs1_reset_coeffs(&coeffs->hs1_coeffs);
	bw_satur_reset_coeffs(&coeffs->satur_coeffs);

#ifdef BW_DEBUG_DEEP
	coeffs->state = bw_drive_coeffs_state_set_sample_rate;
#endif
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state == bw_drive_coeffs_state_set_sample_rate);
}

static inline void bw_drive_reset_coeffs(
		bw_drive_coeffs * BW_RESTRICT coeffs) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_set_sample_rate);

	bw_peak_reset_coeffs(&coeffs->peak_coeffs);
	bw_lp1_reset_coeffs(&coeffs->lp1_coeffs);
	bw_gain_reset_coeffs(&coeffs->gain_coeffs);

#ifdef BW_DEBUG_DEEP
	coeffs->state = bw_drive_coeffs_state_reset_coeffs;
	coeffs->reset_id++;
#endif
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state == bw_drive_coeffs_state_reset_coeffs);
}

static inline float bw_drive_reset_state(
		const bw_drive_coeffs * BW_RESTRICT coeffs,
		bw_drive_state * BW_RESTRICT        state,
		float                               x_0) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT(state != BW_NULL);
	BW_ASSERT(bw_is_finite(x_0));

	float v_lp, v_hp, v_bp;
	bw_svf_reset_state(&coeffs->hp2_coeffs, &state->hp2_state, 0.316f * x_0, &v_lp, &v_bp, &v_hp);
	float y = bw_hs1_reset_state(&coeffs->hs1_coeffs, &state->hs1_state, v_hp);
	y = bw_peak_reset_state(&coeffs->peak_coeffs, &state->peak_state, y);
	y = v_hp + bw_satur_reset_state(&coeffs->satur_coeffs, &state->satur_state, y - v_hp);
	y = bw_lp1_reset_state(&coeffs->lp1_coeffs, &state->lp1_state, y);
	y = bw_gain_get_gain_cur(&coeffs->gain_coeffs) * y;

#ifdef BW_DEBUG_DEEP
	state->hash = bw_hash_sdbm("bw_drive_state");
	state->coeffs_reset_id = coeffs->reset_id;
#endif
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
	BW_ASSERT(bw_is_finite(y));

	return y;
}

static inline void bw_drive_reset_state_multi(
		const bw_drive_coeffs * BW_RESTRICT              coeffs,
		bw_drive_state * BW_RESTRICT const * BW_RESTRICT state,
		const float *                                   x_0,
		float *                                         y_0,
		size_t                                          n_channels) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT(state != BW_NULL);
#ifndef BW_NO_DEBUG
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = i + 1; j < n_channels; j++)
			BW_ASSERT(state[i] != state[j]);
#endif
	BW_ASSERT(x_0 != BW_NULL);

	if (y_0 != BW_NULL)
		for (size_t i = 0; i < n_channels; i++)
			y_0[i] = bw_drive_reset_state(coeffs, state[i], x_0[i]);
	else
		for (size_t i = 0; i < n_channels; i++)
			bw_drive_reset_state(coeffs, state[i], x_0[i]);

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
}

static inline void bw_drive_update_coeffs_ctrl(
		bw_drive_coeffs * BW_RESTRICT coeffs) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);

	bw_peak_update_coeffs_ctrl(&coeffs->peak_coeffs);
	bw_lp1_update_coeffs_ctrl(&coeffs->lp1_coeffs);
	bw_gain_update_coeffs_ctrl(&coeffs->gain_coeffs);

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
}

static inline void bw_drive_update_coeffs_audio(
		bw_drive_coeffs * BW_RESTRICT coeffs) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);

	bw_peak_update_coeffs_audio(&coeffs->peak_coeffs);
	bw_lp1_update_coeffs_audio(&coeffs->lp1_coeffs);
	bw_gain_update_coeffs_audio(&coeffs->gain_coeffs);

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
}

static inline float bw_drive_process1(
		const bw_drive_coeffs * BW_RESTRICT coeffs,
		bw_drive_state * BW_RESTRICT        state,
		float                               x) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT(state != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
	BW_ASSERT(bw_is_finite(x));

	float v_lp, v_hp, v_bp;
	bw_svf_process1(&coeffs->hp2_coeffs, &state->hp2_state, 0.316f * x, &v_lp, &v_bp, &v_hp);
	float y = bw_hs1_process1(&coeffs->hs1_coeffs, &state->hs1_state, v_hp);
	y = bw_peak_process1(&coeffs->peak_coeffs, &state->peak_state, y);
	y = v_hp + bw_satur_process1_comp(&coeffs->satur_coeffs, &state->satur_state, y - v_hp);
	y = bw_lp1_process1(&coeffs->lp1_coeffs, &state->lp1_state, y);
	y = bw_gain_process1(&coeffs->gain_coeffs, y);

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
	BW_ASSERT(bw_is_finite(y));

	return y;
}

static inline void bw_drive_process(
		bw_drive_coeffs * BW_RESTRICT coeffs,
		bw_drive_state * BW_RESTRICT  state,
		const float *                 x,
		float *                       y,
		size_t                        n_samples) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT(state != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
	BW_ASSERT(x != BW_NULL);
	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
	BW_ASSERT(y != BW_NULL);

	bw_drive_update_coeffs_ctrl(coeffs);
	for (size_t i = 0; i < n_samples; i++) {
		bw_drive_update_coeffs_audio(coeffs);
		y[i] = bw_drive_process1(coeffs, state, x[i]);
	}

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
}

static inline void bw_drive_process_multi(
		bw_drive_coeffs * BW_RESTRICT                    coeffs,
		bw_drive_state * BW_RESTRICT const * BW_RESTRICT state,
		const float * const *                            x,
		float * const *                                  y,
		size_t                                           n_channels,
		size_t                                           n_samples) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
	BW_ASSERT(state != BW_NULL);
#ifndef BW_NO_DEBUG
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = i + 1; j < n_channels; j++)
			BW_ASSERT(state[i] != state[j]);
#endif
	BW_ASSERT(x != BW_NULL);
	BW_ASSERT(y != BW_NULL);
#ifndef BW_NO_DEBUG
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = i + 1; j < n_channels; j++)
			BW_ASSERT(y[i] != y[j]);
	for (size_t i = 0; i < n_channels; i++)
		for (size_t j = 0; j < n_channels; j++)
			BW_ASSERT(i == j || x[i] != y[j]);
#endif

	bw_drive_update_coeffs_ctrl(coeffs);
	for (size_t i = 0; i < n_samples; i++) {
		bw_drive_update_coeffs_audio(coeffs);
		for (size_t j = 0; j < n_channels; j++)
			y[j][i] = bw_drive_process1(coeffs, state[j], x[j][i]);
	}

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
}

static inline void bw_drive_set_drive(
		bw_drive_coeffs * BW_RESTRICT coeffs,
		float                         value) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
	BW_ASSERT(bw_is_finite(value));
	BW_ASSERT(value >= 0.f && value <= 1.f);

	bw_peak_set_peak_gain_dB(&coeffs->peak_coeffs, 20.f * value);

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
}

static inline void bw_drive_set_tone(
		bw_drive_coeffs * BW_RESTRICT coeffs,
		float                         value) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
	BW_ASSERT(bw_is_finite(value));
	BW_ASSERT(value >= 0.f && value <= 1.f);

	bw_lp1_set_cutoff(&coeffs->lp1_coeffs, 400.f + (5e3f - 400.f) * value * value * value);

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
}

static inline void bw_drive_set_volume(
		bw_drive_coeffs * BW_RESTRICT coeffs,
		float                         value) {
	BW_ASSERT(coeffs != BW_NULL);
	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
	BW_ASSERT(bw_is_finite(value));
	BW_ASSERT(value >= 0.f && value <= 1.f);

	bw_gain_set_gain_lin(&coeffs->gain_coeffs, value * value * value);

	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
}

static inline char bw_drive_coeffs_is_valid(
		const bw_drive_coeffs * BW_RESTRICT coeffs) {
	BW_ASSERT(coeffs != BW_NULL);

#ifdef BW_DEBUG_DEEP
	if (coeffs->hash != bw_hash_sdbm("bw_drive_coeffs"))
		return 0;
	if (coeffs->state < bw_drive_coeffs_state_init || coeffs->state > bw_drive_coeffs_state_reset_coeffs)
		return 0;
#endif

	return bw_svf_coeffs_is_valid(&coeffs->hp2_coeffs)
		&& bw_hs1_coeffs_is_valid(&coeffs->hs1_coeffs)
		&& bw_peak_coeffs_is_valid(&coeffs->peak_coeffs)
		&& bw_satur_coeffs_is_valid(&coeffs->satur_coeffs)
		&& bw_lp1_coeffs_is_valid(&coeffs->lp1_coeffs)
		&& bw_gain_coeffs_is_valid(&coeffs->gain_coeffs);
}

static inline char bw_drive_state_is_valid(
		const bw_drive_coeffs * BW_RESTRICT coeffs,
		const bw_drive_state * BW_RESTRICT  state) {
	BW_ASSERT(state != BW_NULL);

#ifdef BW_DEBUG_DEEP
	if (state->hash != bw_hash_sdbm("bw_drive_state"))
		return 0;

	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
		return 0;
#endif

	return bw_svf_state_is_valid(coeffs ? &coeffs->hp2_coeffs : BW_NULL, &state->hp2_state)
		&& bw_hs1_state_is_valid(coeffs ? &coeffs->hs1_coeffs : BW_NULL, &state->hs1_state)
		&& bw_peak_state_is_valid(coeffs ? &coeffs->peak_coeffs : BW_NULL, &state->peak_state)
		&& bw_satur_state_is_valid(coeffs ? &coeffs->satur_coeffs : BW_NULL, &state->satur_state)
		&& bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : BW_NULL, &state->lp1_state);
}

#ifdef __cplusplus
}

#ifndef BW_CXX_NO_ARRAY
# include <array>
#endif

namespace Brickworks {

/*** Public C++ API ***/

/*! api_cpp {{{
 *    ##### Brickworks::Drive
 *  ```>>> */
template<size_t N_CHANNELS>
class Drive {
public:
	Drive();

	void setSampleRate(
		float sampleRate);

	void reset(
		float               x0 = 0.f,
		float * BW_RESTRICT y0 = nullptr);

#ifndef BW_CXX_NO_ARRAY
	void reset(
		float                                       x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0);
#endif

	void reset(
		const float * x0,
		float *       y0 = nullptr);

#ifndef BW_CXX_NO_ARRAY
	void reset(
		std::array<float, N_CHANNELS>               x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0 = nullptr);
#endif

	void process(
		const float * const * x,
		float * const *       y,
		size_t                nSamples);

#ifndef BW_CXX_NO_ARRAY
	void process(
		std::array<const float *, N_CHANNELS> x,
		std::array<float *, N_CHANNELS>       y,
		size_t                                nSamples);
#endif

	void setDrive(
		float value);

	void setTone(
		float value);

	void setVolume(
		float value);
/*! <<<...
 *  }
 *  ```
 *  }}} */

/*** 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. */

private:
	bw_drive_coeffs			coeffs;
	bw_drive_state			states[N_CHANNELS];
	bw_drive_state * BW_RESTRICT	statesP[N_CHANNELS];
};

template<size_t N_CHANNELS>
inline Drive<N_CHANNELS>::Drive() {
	bw_drive_init(&coeffs);
	for (size_t i = 0; i < N_CHANNELS; i++)
		statesP[i] = states + i;
}

template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::setSampleRate(
		float sampleRate) {
	bw_drive_set_sample_rate(&coeffs, sampleRate);
}

template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::reset(
		float               x0,
		float * BW_RESTRICT y0) {
	bw_drive_reset_coeffs(&coeffs);
	if (y0 != nullptr)
		for (size_t i = 0; i < N_CHANNELS; i++)
			y0[i] = bw_drive_reset_state(&coeffs, states + i, x0);
	else
		for (size_t i = 0; i < N_CHANNELS; i++)
			bw_drive_reset_state(&coeffs, states + i, x0);
}

#ifndef BW_CXX_NO_ARRAY
template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::reset(
		float                                       x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0) {
	reset(x0, y0 != nullptr ? y0->data() : nullptr);
}
#endif

template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::reset(
		const float * x0,
		float *       y0) {
	bw_drive_reset_coeffs(&coeffs);
	bw_drive_reset_state_multi(&coeffs, statesP, x0, y0, N_CHANNELS);
}

#ifndef BW_CXX_NO_ARRAY
template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::reset(
		std::array<float, N_CHANNELS>               x0,
		std::array<float, N_CHANNELS> * BW_RESTRICT y0) {
	reset(x0.data(), y0 != nullptr ? y0->data() : nullptr);
}
#endif

template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::process(
		const float * const * x,
		float * const *       y,
		size_t                nSamples) {
	bw_drive_process_multi(&coeffs, statesP, x, y, N_CHANNELS, nSamples);
}

#ifndef BW_CXX_NO_ARRAY
template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::process(
		std::array<const float *, N_CHANNELS> x,
		std::array<float *, N_CHANNELS>       y,
		size_t                                nSamples) {
	process(x.data(), y.data(), nSamples);
}
#endif

template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::setDrive(
		float value) {
	bw_drive_set_drive(&coeffs, value);
}

template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::setTone(
		float value) {
	bw_drive_set_tone(&coeffs, value);
}

template<size_t N_CHANNELS>
inline void Drive<N_CHANNELS>::setVolume(
		float value) {
	bw_drive_set_volume(&coeffs, value);
}

}
#endif

#endif