From baf440a171c8e58fc7772c28f74abe38605f139a Mon Sep 17 00:00:00 2001
From: Stefano D'Angelo <s@dangelo.audio>
Date: Mon, 18 Sep 2023 13:41:15 +0200
Subject: [PATCH] finalized bw_phase_gen + updated synth(pp)_simple + better
 bw_svf doc

---
 TODO                                          |   2 +
 .../src/bw_example_synth_simple.c             |   8 +-
 examples/synth_simple/vst3/Makefile           |   3 +
 examples/synthpp_simple/vst3/Makefile         |   3 +
 include/bw_phase_gen.h                        | 670 +++++++++++++++---
 include/bw_svf.h                              |   4 +-
 6 files changed, 585 insertions(+), 105 deletions(-)

diff --git a/TODO b/TODO
index 79024e4..85c718e 100644
--- a/TODO
+++ b/TODO
@@ -28,6 +28,7 @@ finally:
 * state that you need different output buffers to reset
 * thank scientific paper authors
 * change config.h in examples version 1.0.0
+* "Templates must have C++ linkage"?
 
 build system:
 * single header generation (vs modules in bwp... to think about)
@@ -75,6 +76,7 @@ code:
 * get current compression level, knee
 * src inside distortions? w/ control from outside?
 * make all outs nullable?
+* make all reset state outs nullable (svf, phase_gen, ...)?
 
 build system:
 * make makefiles handle paths with spaces etc
diff --git a/examples/synth_simple/src/bw_example_synth_simple.c b/examples/synth_simple/src/bw_example_synth_simple.c
index 4669088..008dd8d 100644
--- a/examples/synth_simple/src/bw_example_synth_simple.c
+++ b/examples/synth_simple/src/bw_example_synth_simple.c
@@ -44,16 +44,18 @@ void bw_example_synth_simple_set_sample_rate(bw_example_synth_simple *instance,
 
 void bw_example_synth_simple_reset(bw_example_synth_simple *instance) {
 	bw_phase_gen_reset_coeffs(&instance->phase_gen_coeffs);
-	bw_phase_gen_reset_state(&instance->phase_gen_coeffs, &instance->phase_gen_state, 0.f);
+	float p, inc;
+	bw_phase_gen_reset_state(&instance->phase_gen_coeffs, &instance->phase_gen_state, 0.f, &p, &inc);
 	bw_osc_pulse_reset_coeffs(&instance->osc_pulse_coeffs);
 	bw_osc_filt_reset_state(&instance->osc_filt_state);
 	bw_svf_reset_coeffs(&instance->svf_coeffs);
-	bw_svf_reset_state(&instance->svf_coeffs, &instance->svf_state, 0.f);
+	float lp, bp, hp;
+	bw_svf_reset_state(&instance->svf_coeffs, &instance->svf_state, 0.f, &lp, &bp, &hp);
 	bw_env_gen_reset_coeffs(&instance->env_gen_coeffs);
 	bw_env_gen_reset_state(&instance->env_gen_coeffs, &instance->env_gen_state);
 	bw_gain_reset_coeffs(&instance->gain_coeffs);
 	bw_ppm_reset_coeffs(&instance->ppm_coeffs);
-	bw_ppm_reset_state(&instance->ppm_coeffs, &instance->ppm_state);
+	bw_ppm_reset_state(&instance->ppm_coeffs, &instance->ppm_state, 0.f);
 	instance->note = -1;
 }
 
diff --git a/examples/synth_simple/vst3/Makefile b/examples/synth_simple/vst3/Makefile
index 070f1ba..e3d8d91 100644
--- a/examples/synth_simple/vst3/Makefile
+++ b/examples/synth_simple/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_synth_simple
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_synth_simple.c
 
 include ${ROOT_DIR}/../../common/vst3/vst3.mk
+
+CXXFLAGS += -DRELEASE=1 -DNDEBUG -DBW_NO_DEBUG
+#CXXFLAGS += -DDEVELOPMENT=1 -DBW_DEBUG_DEEP
diff --git a/examples/synthpp_simple/vst3/Makefile b/examples/synthpp_simple/vst3/Makefile
index 02790dc..ec6e210 100644
--- a/examples/synthpp_simple/vst3/Makefile
+++ b/examples/synthpp_simple/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_synthpp_simple
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_synthpp_simple.cpp
 
 include ${ROOT_DIR}/../../common/vst3/vst3.mk
+
+CXXFLAGS += -DRELEASE=1 -DNDEBUG -DBW_NO_DEBUG
+#CXXFLAGS += -DDEVELOPMENT=1 -DBW_DEBUG_DEEP
diff --git a/include/bw_phase_gen.h b/include/bw_phase_gen.h
index e8b77bd..d66be6c 100644
--- a/include/bw_phase_gen.h
+++ b/include/bw_phase_gen.h
@@ -31,6 +31,14 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
+ *          <li>Added initial input value to
+ *              <code>bw_phase_gen_reset_state()</code>.</li>
+ *          <li>Added <code>bw_phase_gen_reset_state_multi()</code> and updated
+ *              C++ API in this regard.</li>
+ *          <li>Now <code>bw_phase_gen_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_phase_gen_process()</code> and
  *              <code>bw_phase_gen_process_multi()</code> now use
  *              <code>size_t</code> to count samples and channels.</li>
@@ -39,7 +47,11 @@
  *          <li>Moved C++ code to C header.</li>
  *          <li>Added overloaded C++ <code>process()</code> function taking
  *              C-style arrays as arguments.</li>
+ *          <li>Fixed smoothing coefficients update in
+ *              <code>bw_phase_gen_reset_coeffs()</code>.</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>:
@@ -102,58 +114,105 @@ typedef struct bw_phase_gen_state bw_phase_gen_state;
  *
  *    #### bw_phase_gen_init()
  *  ```>>> */
-static inline void bw_phase_gen_init(bw_phase_gen_coeffs *BW_RESTRICT coeffs);
+static inline void bw_phase_gen_init(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Initializes input parameter values in `coeffs`.
  *
  *    #### bw_phase_gen_set_sample_rate()
  *  ```>>> */
-static inline void bw_phase_gen_set_sample_rate(bw_phase_gen_coeffs *BW_RESTRICT coeffs, float sample_rate);
+static inline void bw_phase_gen_set_sample_rate(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	float                             sample_rate);
 /*! <<<```
  *    Sets the `sample_rate` (Hz) value in `coeffs`.
  *
  *    #### bw_phase_gen_reset_coeffs()
  *  ```>>> */
-static inline void bw_phase_gen_reset_coeffs(bw_phase_gen_coeffs *BW_RESTRICT coeffs);
+static inline void bw_phase_gen_reset_coeffs(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Resets coefficients in `coeffs` to assume their target values.
  *
  *    #### bw_phase_gen_reset_state()
  *  ```>>> */
-static inline void bw_phase_gen_reset_state(const bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, float phase_0);
+static inline void bw_phase_gen_reset_state(
+	const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	bw_phase_gen_state * BW_RESTRICT        state,
+	float                                   phase_0,
+	float * BW_RESTRICT                     y_0,
+	float * BW_RESTRICT                     y_inc_0);
 /*! <<<```
- *    Resets the given `state` to its initial values using the given `coeffs`.
+ *    Resets the given `state` to its initial values using the given `coeffs`
+ *    and the initial phase value `phase_0`.
+ *
+ *    The corresponding initial output and phase increment values are put into
+ *    `y_0` and `y_inc_0` respectively.
+ *
+ *    #### bw_phase_gen_reset_state_multi()
+ *  ```>>> */
+static inline void bw_phase_gen_reset_state_multi(
+	const bw_phase_gen_coeffs * BW_RESTRICT              coeffs,
+	bw_phase_gen_state * BW_RESTRICT const * BW_RESTRICT state,
+	const float *                                        phase_0,
+	float *                                              y_0,
+	float *                                              y_inc_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 phase value in the `phase_0`
+ *    array.
+ *
+ *    The corresponding initial output and phase increment values are put into
+ *    the `y_0` and `y_inc_0` arrays, respectively, if they are not `NULL`.
  *
  *    #### bw_phase_gen_update_coeffs_ctrl()
  *  ```>>> */
-static inline void bw_phase_gen_update_coeffs_ctrl(bw_phase_gen_coeffs *BW_RESTRICT coeffs);
+static inline void bw_phase_gen_update_coeffs_ctrl(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers control-rate update of coefficients in `coeffs`.
  *
  *    #### bw_phase_gen_update_coeffs_audio()
  *  ```>>> */
-static inline void bw_phase_gen_update_coeffs_audio(bw_phase_gen_coeffs *BW_RESTRICT coeffs);
+static inline void bw_phase_gen_update_coeffs_audio(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers audio-rate update of coefficients in `coeffs`.
  *
  *    #### bw_phase_gen_process1\*()
  *  ```>>> */
-static inline void bw_phase_gen_process1(const bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, float *BW_RESTRICT y, float *BW_RESTRICT y_phase_inc);
-static inline void bw_phase_gen_process1_mod(const bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, float x_mod, float *BW_RESTRICT y, float *BW_RESTRICT y_phase_inc);
+static inline void bw_phase_gen_process1(
+	const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	bw_phase_gen_state * BW_RESTRICT        state,
+	float * BW_RESTRICT                     y,
+	float * BW_RESTRICT                     y_inc);
+
+static inline void bw_phase_gen_process1_mod(
+	const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	bw_phase_gen_state * BW_RESTRICT        state,
+	float                                   x_mod,
+	float * BW_RESTRICT                     y,
+	float * BW_RESTRICT                     y_inc);
 /*! <<<```
- *    These functions generate and return one sample using `coeffs`, while using
- *    and updating `state`, and put the corresponding phase increment value in
- *    `y_phase_inc`.
+ *    These functions generate one output sample using `coeffs`, while using
+ *    and updating `state`, putting its value in `y` and the corresponding phase
+ *    increment value in `y_inc`.
  *
  *    In particular:
- *     * `bw_phase_gen_process1()` does not apply exponential frequency
- *       modulation;
+ *     * `bw_phase_gen_process1()` does not apply frequency modulation;
  *     * `bw_phase_gen_process1_mod()` applies exponential frequency modulation
  *       using `x_mod` as modulation input (scale `1.f`/octave).
  *
  *    #### bw_phase_gen_process()
  *  ```>>> */
-static inline void bw_phase_gen_process(bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, const float *x_mod, float *y, float *y_phase_inc, size_t n_samples);
+static inline void bw_phase_gen_process(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	bw_phase_gen_state * BW_RESTRICT  state,
+	const float *                     x_mod,
+	float *                           y,
+	float *                           y_inc,
+	size_t                            n_samples);
 /*! <<<```
  *    Generates and fills the first `n_samples` of the output buffer `y`, while
  *    using and updating both `coeffs` and `state` (control and audio rate).
@@ -165,7 +224,14 @@ static inline void bw_phase_gen_process(bw_phase_gen_coeffs *BW_RESTRICT coeffs,
  *
  *    #### bw_phase_gen_process_multi()
  *  ```>>> */
-static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x_mod, float * const *y, float * const *y_phase_inc, size_t n_channels, size_t n_samples);
+static inline void bw_phase_gen_process_multi(
+	bw_phase_gen_coeffs * BW_RESTRICT                    coeffs,
+	bw_phase_gen_state * BW_RESTRICT const * BW_RESTRICT state,
+	const float * const *                                x_mod,
+	float * const *                                      y,
+	float * const *                                      y_inc,
+	size_t                                               n_channels,
+	size_t                                               n_samples);
 /*! <<<```
  *    Generates and fills the first `n_samples` of the `n_channels` output
  *    buffers `y`, while using and updating both the common `coeffs` and each of
@@ -180,19 +246,55 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
  *
  *    #### bw_phase_gen_set_frequency()
  *  ```>>> */
-static inline void bw_phase_gen_set_frequency(bw_phase_gen_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_phase_gen_set_frequency(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	float                             value);
 /*! <<<```
  *    Sets the base frequency to `value` (Hz) in `coeffs`.
- *    
+ *
+ *    `value` must be finite.
+ *
  *    Default value: `1.f`.
  *
  *    #### bw_phase_gen_set_portamento_tau()
  *  ```>>> */
-static inline void bw_phase_gen_set_portamento_tau(bw_phase_gen_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_phase_gen_set_portamento_tau(
+	bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	float                             value);
 /*! <<<```
  *    Sets the portamento time constant `value` (s) in `coeffs`.
  *
+ *    `value` must be non-negative.
+ *
  *    Default value: `0.f`.
+ *
+ *    #### bw_phase_gen_coeffs_is_valid()
+ *  ```>>> */
+static inline char bw_phase_gen_coeffs_is_valid(
+	const bw_phase_gen_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_phase_gen_coeffs`.
+ *
+ *    #### bw_phase_gen_state_is_valid()
+ *  ```>>> */
+static inline char bw_phase_gen_state_is_valid(
+	const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+	const bw_phase_gen_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 `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_phase_gen_state`.
  *  }}} */
 
 #ifdef __cplusplus
@@ -211,36 +313,82 @@ static inline void bw_phase_gen_set_portamento_tau(bw_phase_gen_coeffs *BW_RESTR
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_phase_gen_coeffs_state {
+	bw_phase_gen_coeffs_state_invalid,
+	bw_phase_gen_coeffs_state_init,
+	bw_phase_gen_coeffs_state_set_sample_rate,
+	bw_phase_gen_coeffs_state_reset_coeffs
+};
+#endif
+
 struct bw_phase_gen_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_phase_gen_coeffs_state	state;
+	uint32_t			reset_id;
+#endif
+
 	// Sub-components
-	bw_one_pole_coeffs	portamento_coeffs;
-	bw_one_pole_state	portamento_state;
+	bw_one_pole_coeffs		portamento_coeffs;
+	bw_one_pole_state		portamento_state;
 
 	// Coefficients
-	float			T;
+	float				T;
 
-	float			portamento_target;
+	float				portamento_target;
 
 	// Parameters
-	float			frequency;
-	float			frequency_prev;
+	float				frequency;
+	float				frequency_prev;
 };
 
 struct bw_phase_gen_state {
-	float	phase;
+#ifdef BW_DEBUG_DEEP
+	uint32_t	hash;
+	uint32_t	coeffs_reset_id;
+#endif
+
+	// States
+	float		phase;
 };
 
-static inline void bw_phase_gen_init(bw_phase_gen_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_phase_gen_init(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
 	bw_one_pole_init(&coeffs->portamento_coeffs);
 	coeffs->frequency = 1.f;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_phase_gen_coeffs");
+	coeffs->state = bw_phase_gen_coeffs_state_init;
+	coeffs->reset_id = coeffs->hash + 1;
+#endif
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_phase_gen_coeffs_state_init);
 }
 
-static inline void bw_phase_gen_set_sample_rate(bw_phase_gen_coeffs *BW_RESTRICT coeffs, float sample_rate) {
+static inline void bw_phase_gen_set_sample_rate(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		float                             sample_rate) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
+
 	bw_one_pole_set_sample_rate(&coeffs->portamento_coeffs, sample_rate);
 	coeffs->T = 1.f / sample_rate;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_phase_gen_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_phase_gen_coeffs_state_set_sample_rate);
 }
 
-static inline void bw_phase_gen_do_update_coeffs_ctrl(bw_phase_gen_coeffs *BW_RESTRICT coeffs, char force) {
+static inline void bw_phase_gen_do_update_coeffs_ctrl(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs, char force) {
 	bw_one_pole_update_coeffs_ctrl(&coeffs->portamento_coeffs);
 	if (force || coeffs->frequency != coeffs->frequency_prev) {
 		coeffs->portamento_target = coeffs->T * coeffs->frequency;
@@ -248,49 +396,197 @@ static inline void bw_phase_gen_do_update_coeffs_ctrl(bw_phase_gen_coeffs *BW_RE
 	}
 }
 
-static inline void bw_phase_gen_reset_coeffs(bw_phase_gen_coeffs *BW_RESTRICT coeffs) {
-	bw_phase_gen_do_update_coeffs_ctrl(coeffs, 1);
+static inline void bw_phase_gen_reset_coeffs(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_set_sample_rate);
+
 	bw_one_pole_reset_coeffs(&coeffs->portamento_coeffs);
+	bw_phase_gen_do_update_coeffs_ctrl(coeffs, 1);
 	bw_one_pole_reset_state(&coeffs->portamento_coeffs, &coeffs->portamento_state, coeffs->portamento_target);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_phase_gen_coeffs_state_reset_coeffs;
+	coeffs->reset_id++;
+#endif
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_phase_gen_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_phase_gen_reset_state(const bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, float phase_0) {
-	(void)coeffs;
+static inline void bw_phase_gen_reset_state(
+		const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		bw_phase_gen_state * BW_RESTRICT        state,
+		float                                   phase_0,
+		float * BW_RESTRICT                     y_0,
+		float * BW_RESTRICT                     y_inc_0) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(bw_is_finite(phase_0));
+	BW_ASSERT(y_0 != NULL);
+	BW_ASSERT(y_inc_0 != NULL);
+
 	state->phase = phase_0;
+	*y_inc_0 = bw_one_pole_get_y_z1(&coeffs->portamento_state);
+	*y_0 = phase_0;
+
+#ifdef BW_DEBUG_DEEP
+	state->hash = bw_hash_sdbm("bw_phase_gen_state");
+	state->coeffs_reset_id = coeffs->reset_id;
+#endif
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(*y_0));
+	BW_ASSERT(bw_is_finite(*y_inc_0));
 }
 
-static inline void bw_phase_gen_update_coeffs_ctrl(bw_phase_gen_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_phase_gen_reset_state_multi(
+		const bw_phase_gen_coeffs * BW_RESTRICT              coeffs,
+		bw_phase_gen_state * BW_RESTRICT const * BW_RESTRICT state,
+		const float *                                        phase_0,
+		float *                                              y_0,
+		float *                                              y_inc_0,
+		size_t                                               n_channels) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(phase_0 != NULL);
+
+	if (y_0 != NULL) {
+		if (y_inc_0 != NULL) {
+			for (size_t i = 0; i < n_channels; i++)
+				bw_phase_gen_reset_state(coeffs, state[i], phase_0[i], y_0 + i, y_inc_0 + i);
+		} else {
+			for (size_t i = 0; i < n_channels; i++) {
+				float v_inc;
+				bw_phase_gen_reset_state(coeffs, state[i], phase_0[i], y_0 + i, &v_inc);
+			}
+		}
+	} else {
+		if (y_inc_0 != NULL) {
+			for (size_t i = 0; i < n_channels; i++) {
+				float v;
+				bw_phase_gen_reset_state(coeffs, state[i], phase_0[i], &v, y_inc_0 + i);
+			}
+		} else {
+			for (size_t i = 0; i < n_channels; i++) {
+				float v, v_inc;
+				bw_phase_gen_reset_state(coeffs, state[i], phase_0[i], &v, &v_inc);
+			}
+		}
+	}
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_inc_0 != NULL ? bw_has_only_finite(y_inc_0, n_channels) : 1);
+}
+
+static inline void bw_phase_gen_update_coeffs_ctrl(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+
 	bw_phase_gen_do_update_coeffs_ctrl(coeffs, 0);
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_phase_gen_update_coeffs_audio(bw_phase_gen_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_phase_gen_update_coeffs_audio(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+
 	bw_one_pole_process1(&coeffs->portamento_coeffs, &coeffs->portamento_state, coeffs->portamento_target);
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
 }
 
-static inline float _bw_phase_gen_update_phase(bw_phase_gen_state *BW_RESTRICT state, float phase_inc) {
-	state->phase += phase_inc;
+static inline float bw_phase_gen_update_phase(
+		bw_phase_gen_state * BW_RESTRICT state,
+		float                            inc) {
+	state->phase += inc;
 	state->phase -= bw_floorf(state->phase);
 	return state->phase;
 }
 
-static inline void bw_phase_gen_process1(const bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, float *BW_RESTRICT y, float *BW_RESTRICT y_phase_inc) {
-	*y_phase_inc = bw_one_pole_get_y_z1(&coeffs->portamento_state);
-	*y = _bw_phase_gen_update_phase(state, *y_phase_inc);
+static inline void bw_phase_gen_process1(
+		const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		bw_phase_gen_state * BW_RESTRICT        state,
+		float * BW_RESTRICT                     y,
+		float * BW_RESTRICT                     y_inc) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
+	BW_ASSERT(y != NULL);
+	BW_ASSERT(y_inc != NULL);
+
+	*y_inc = bw_one_pole_get_y_z1(&coeffs->portamento_state);
+	*y = bw_phase_gen_update_phase(state, *y_inc);
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(*y));
+	BW_ASSERT(bw_is_finite(*y_inc));
 }
 
-static inline void bw_phase_gen_process1_mod(const bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, float x_mod, float *BW_RESTRICT y, float *BW_RESTRICT y_phase_inc) {
-	*y_phase_inc = bw_one_pole_get_y_z1(&coeffs->portamento_state) * bw_pow2f(x_mod);
-	*y = _bw_phase_gen_update_phase(state, *y_phase_inc);
+static inline void bw_phase_gen_process1_mod(
+		const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		bw_phase_gen_state * BW_RESTRICT        state,
+		float                                   x_mod,
+		float * BW_RESTRICT                     y,
+		float * BW_RESTRICT                     y_inc) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(x_mod));
+	BW_ASSERT(y != NULL);
+	BW_ASSERT(y_inc != NULL);
+
+	*y_inc = bw_one_pole_get_y_z1(&coeffs->portamento_state) * bw_pow2f(x_mod);
+	*y = bw_phase_gen_update_phase(state, *y_inc);
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(*y));
+	BW_ASSERT(bw_is_finite(*y_inc));
 }
 
-static inline void bw_phase_gen_process(bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT state, const float *x_mod, float* y, float *y_phase_inc, size_t n_samples) {
+static inline void bw_phase_gen_process(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		bw_phase_gen_state * BW_RESTRICT  state,
+		const float *                     x_mod,
+		float *                           y,
+		float *                           y_inc,
+		size_t                            n_samples) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(x_mod != NULL ? bw_has_only_finite(x_mod, n_samples) : 1);
+
 	bw_phase_gen_update_coeffs_ctrl(coeffs);
 	if (y != NULL) {
 		if (x_mod != NULL) {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
-					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], y + i, y_phase_inc + i);
+					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], y + i, y_inc + i);
 				}
 			else
 				for (size_t i = 0; i < n_samples; i++) {
@@ -299,10 +595,10 @@ static inline void bw_phase_gen_process(bw_phase_gen_coeffs *BW_RESTRICT coeffs,
 					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], y + i, &v_phase_inc);
 				}
 		} else {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
-					bw_phase_gen_process1(coeffs, state, y + i, y_phase_inc + i);
+					bw_phase_gen_process1(coeffs, state, y + i, y_inc + i);
 				}
 			else
 				for (size_t i = 0; i < n_samples; i++) {
@@ -313,11 +609,11 @@ static inline void bw_phase_gen_process(bw_phase_gen_coeffs *BW_RESTRICT coeffs,
 		}
 	} else {
 		if (x_mod != NULL) {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					float v;
-					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], &v, y_phase_inc + i);
+					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], &v, y_inc + i);
 				}
 			else
 				for (size_t i = 0; i < n_samples; i++) {
@@ -326,11 +622,11 @@ static inline void bw_phase_gen_process(bw_phase_gen_coeffs *BW_RESTRICT coeffs,
 					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], &v, &v_phase_inc);
 				}
 		} else {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					float v;
-					bw_phase_gen_process1(coeffs, state, &v, y_phase_inc + i);
+					bw_phase_gen_process1(coeffs, state, &v, y_inc + i);
 				}
 			else
 				for (size_t i = 0; i < n_samples; i++) {
@@ -340,13 +636,31 @@ static inline void bw_phase_gen_process(bw_phase_gen_coeffs *BW_RESTRICT coeffs,
 				}
 		}
 	}
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(y != NULL ? bw_has_only_finite(y, n_samples) : 1);
+	BW_ASSERT_DEEP(y_inc != NULL ? bw_has_only_finite(y_inc, n_samples) : 1);
 }
 
-static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT coeffs, bw_phase_gen_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x_mod, float * const *y, float * const *y_phase_inc, size_t n_channels, size_t n_samples) {
+static inline void bw_phase_gen_process_multi(
+		bw_phase_gen_coeffs * BW_RESTRICT                    coeffs,
+		bw_phase_gen_state * BW_RESTRICT const * BW_RESTRICT state,
+		const float * const *                                x_mod,
+		float * const *                                      y,
+		float * const *                                      y_inc,
+		size_t                                               n_channels,
+		size_t                                               n_samples) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+
 	bw_phase_gen_update_coeffs_ctrl(coeffs);
 	if (y != NULL) {
 		if (x_mod != NULL) {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -357,8 +671,8 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
 							bw_phase_gen_process1(coeffs, state[j], &v, &v_phase_inc);
 						if (y[j])
 							y[j][i] = v;
-						if (y_phase_inc[j])
-							y_phase_inc[j][i] = v_phase_inc;
+						if (y_inc[j])
+							y_inc[j][i] = v_phase_inc;
 					}
 				}
 			else
@@ -375,7 +689,7 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
 					}
 				}
 		} else {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -383,8 +697,8 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
 						bw_phase_gen_process1(coeffs, state[j], &v, &v_phase_inc);
 						if (y[j])
 							y[j][i] = v;
-						if (y_phase_inc[j])
-							y_phase_inc[j][i] = v_phase_inc;
+						if (y_inc[j])
+							y_inc[j][i] = v_phase_inc;
 					}
 				}
 			else
@@ -400,7 +714,7 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
 		}
 	} else {
 		if (x_mod != NULL) {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -409,8 +723,8 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
 							bw_phase_gen_process1_mod(coeffs, state[j], x_mod[j][i], &v, &v_phase_inc);
 						else
 							bw_phase_gen_process1(coeffs, state[j], &v, &v_phase_inc);
-						if (y_phase_inc[j])
-							y_phase_inc[j][i] = v_phase_inc;
+						if (y_inc[j])
+							y_inc[j][i] = v_phase_inc;
 					}
 				}
 			else
@@ -425,14 +739,14 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
 					}
 				}
 		} else {
-			if (y_phase_inc != NULL)
+			if (y_inc != NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
 						float v, v_phase_inc;
 						bw_phase_gen_process1(coeffs, state[j], &v, &v_phase_inc);
-						if (y_phase_inc[j])
-							y_phase_inc[j][i] = v_phase_inc;
+						if (y_inc[j])
+							y_inc[j][i] = v_phase_inc;
 					}
 				}
 			else
@@ -445,14 +759,93 @@ static inline void bw_phase_gen_process_multi(bw_phase_gen_coeffs *BW_RESTRICT c
 				}
 		}
 	}
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_phase_gen_set_frequency(bw_phase_gen_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_phase_gen_set_frequency(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		float                             value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+
 	coeffs->frequency = value;
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
 }
 
-static inline void bw_phase_gen_set_portamento_tau(bw_phase_gen_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_phase_gen_set_portamento_tau(
+		bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		float                             value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+	BW_ASSERT(value >= 0.f);
+
 	bw_one_pole_set_tau(&coeffs->portamento_coeffs, value);
+
+	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
+}
+
+static inline char bw_phase_gen_coeffs_is_valid(
+		const bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->hash != bw_hash_sdbm("bw_phase_gen_coeffs"))
+		return 0;
+	if (coeffs->state < bw_phase_gen_coeffs_state_init || coeffs->state > bw_phase_gen_coeffs_state_reset_coeffs)
+		return 0;
+#endif
+
+	if (!bw_is_finite(coeffs->frequency))
+		return 0;
+
+	if (!bw_one_pole_coeffs_is_valid(&coeffs->portamento_coeffs))
+		return 0;
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->state >= bw_phase_gen_coeffs_state_set_sample_rate) {
+		if (!bw_is_finite(coeffs->T) || coeffs->T <= 0.f)
+			return 0;
+	}
+
+	if (coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs) {
+		if (!bw_is_finite(coeffs->portamento_target) || coeffs->portamento_target < 0.f)
+			return 0;
+		if (!bw_is_finite(coeffs->frequency_prev))
+			return 0;
+
+		if (!bw_one_pole_state_is_valid(&coeffs->portamento_coeffs, &coeffs->portamento_state))
+			return 0;
+	}
+#endif
+
+	return 1;
+}
+
+static inline char bw_phase_gen_state_is_valid(
+		const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
+		const bw_phase_gen_state * BW_RESTRICT  state) {
+	BW_ASSERT(state != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (state->hash != bw_hash_sdbm("bw_phase_gen_state"))
+		return 0;
+
+	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+		return 0;
+#endif
+
+	(void)coeffs;
+
+	return bw_is_finite(state->phase) && state->phase >= 0.f && state->phase < 1.f;
 }
 
 #ifdef __cplusplus
@@ -472,21 +865,46 @@ class PhaseGen {
 public:
 	PhaseGen();
 
-	void setSampleRate(float sampleRate);
-	void reset(float phase_0 = 0.f);
-	void process(
-		const float * const *x_mod,
-		float * const *y,
-		float * const *y_phase_inc,
-		size_t nSamples);
-	void process(
-		std::array<const float *, N_CHANNELS> x_mod,
-		std::array<float *, N_CHANNELS> y,
-		std::array<float *, N_CHANNELS> y_phase_inc,
-		size_t nSamples);
+	void setSampleRate(
+		float sampleRate);
 
-	void setFrequency(float value);
-	void setPortamentoTau(float value);
+	void reset(
+		float               phase0 = 0.f,
+		float * BW_RESTRICT y0 = nullptr,
+		float * BW_RESTRICT yInc0 = nullptr);
+
+	void reset(
+		float                                       phase0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT yInc0);
+
+	void reset(
+		const float * phase0,
+		float *       y0 = nullptr,
+		float *       yInc0 = nullptr);
+
+	void reset(
+		std::array<float, N_CHANNELS>               phase0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0 = nullptr,
+		std::array<float, N_CHANNELS> * BW_RESTRICT yInc0 = nullptr);
+
+	void process(
+		const float * const * xMod,
+		float * const *       y,
+		float * const *       yInc,
+		size_t                nSamples);
+
+	void process(
+		std::array<const float *, N_CHANNELS> xMod,
+		std::array<float *, N_CHANNELS>       y,
+		std::array<float *, N_CHANNELS>       yInc,
+		size_t                                nSamples);
+
+	void setFrequency(
+		float value);
+
+	void setPortamentoTau(
+		float value);
 /*! <<<...
  *  }
  *  ```
@@ -498,9 +916,9 @@ public:
  * change at any time in future versions. Please, do not use it directly. */
 
 private:
-	bw_phase_gen_coeffs	 coeffs;
-	bw_phase_gen_state	 states[N_CHANNELS];
-	bw_phase_gen_state	*BW_RESTRICT statesP[N_CHANNELS];
+	bw_phase_gen_coeffs			coeffs;
+	bw_phase_gen_state			states[N_CHANNELS];
+	bw_phase_gen_state * BW_RESTRICT	statesP[N_CHANNELS];
 };
 
 template<size_t N_CHANNELS>
@@ -511,42 +929,94 @@ inline PhaseGen<N_CHANNELS>::PhaseGen() {
 }
 
 template<size_t N_CHANNELS>
-inline void PhaseGen<N_CHANNELS>::setSampleRate(float sampleRate) {
+inline void PhaseGen<N_CHANNELS>::setSampleRate(
+		float sampleRate) {
 	bw_phase_gen_set_sample_rate(&coeffs, sampleRate);
 }
 
 template<size_t N_CHANNELS>
-inline void PhaseGen<N_CHANNELS>::reset(float phase_0) {
+inline void PhaseGen<N_CHANNELS>::reset(
+		float               phase0,
+		float * BW_RESTRICT y0,
+		float * BW_RESTRICT yInc0) {
 	bw_phase_gen_reset_coeffs(&coeffs);
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_phase_gen_reset_state(&coeffs, states + i, phase_0);
+	if (y0 != nullptr) {
+		if (yInc0 != nullptr) {
+			for (size_t i = 0; i < N_CHANNELS; i++)
+				bw_phase_gen_reset_state(&coeffs, states + i, phase0, y0 + i, yInc0 + i);
+		} else {
+			for (size_t i = 0; i < N_CHANNELS; i++) {
+				float vInc;
+				bw_phase_gen_reset_state(&coeffs, states + i, phase0, y0 + i, &vInc);
+			}
+		}
+	} else {
+		if (yInc0 != nullptr) {
+			for (size_t i = 0; i < N_CHANNELS; i++) {
+				float v;
+				bw_phase_gen_reset_state(&coeffs, states + i, phase0, &v, yInc0 + i);
+			}
+		} else {
+			for (size_t i = 0; i < N_CHANNELS; i++) {
+				float v, vInc;
+				bw_phase_gen_reset_state(&coeffs, states + i, phase0, &v, &vInc);
+			}
+		}
+	}
+}
+
+template<size_t N_CHANNELS>
+inline void PhaseGen<N_CHANNELS>::reset(
+		float                                       phase0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT yInc0) {
+	reset(phase0, y0 != nullptr ? y0.data() : nullptr, yInc0 != nullptr ? yInc0.data() : nullptr);
+}
+
+template<size_t N_CHANNELS>
+inline void PhaseGen<N_CHANNELS>::reset(
+		const float * phase0,
+		float *       y0,
+		float *       yInc0) {
+	bw_phase_gen_reset_coeffs(&coeffs);
+	bw_phase_gen_reset_state_multi(&coeffs, statesP, phase0, y0, yInc0, N_CHANNELS);
+}
+
+template<size_t N_CHANNELS>
+inline void PhaseGen<N_CHANNELS>::reset(
+		std::array<float, N_CHANNELS>               phase0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT yInc0) {
+	reset(phase0.data(), y0 != nullptr ? y0.data() : nullptr, yInc0 != nullptr ? yInc0.data() : nullptr);
 }
 
 template<size_t N_CHANNELS>
 inline void PhaseGen<N_CHANNELS>::process(
-		const float * const *x_mod,
-		float * const *y,
-		float * const *y_phase_inc,
-		size_t nSamples) {
-	bw_phase_gen_process_multi(&coeffs, statesP, x_mod, y, y_phase_inc, N_CHANNELS, nSamples);
+		const float * const * xMod,
+		float * const *       y,
+		float * const *       yInc,
+		size_t                nSamples) {
+	bw_phase_gen_process_multi(&coeffs, statesP, xMod, y, yInc, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void PhaseGen<N_CHANNELS>::process(
-		std::array<const float *, N_CHANNELS> x_mod,
-		std::array<float *, N_CHANNELS> y,
-		std::array<float *, N_CHANNELS> y_phase_inc,
-		size_t nSamples) {
-	process(x_mod.data(), y.data(), y_phase_inc.data(), nSamples);
+		std::array<const float *, N_CHANNELS> xMod,
+		std::array<float *, N_CHANNELS>       y,
+		std::array<float *, N_CHANNELS>       yInc,
+		size_t                                nSamples) {
+	process(xMod.data(), y.data(), yInc.data(), nSamples);
 }
 
 template<size_t N_CHANNELS>
-inline void PhaseGen<N_CHANNELS>::setFrequency(float value) {
+inline void PhaseGen<N_CHANNELS>::setFrequency(
+		float value) {
 	bw_phase_gen_set_frequency(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void PhaseGen<N_CHANNELS>::setPortamentoTau(float value) {
+inline void PhaseGen<N_CHANNELS>::setPortamentoTau(
+		float value) {
 	bw_phase_gen_set_portamento_tau(&coeffs, value);
 }
 
diff --git a/include/bw_svf.h b/include/bw_svf.h
index b4a28c1..e2212da 100644
--- a/include/bw_svf.h
+++ b/include/bw_svf.h
@@ -180,8 +180,8 @@ static inline void bw_svf_reset_state_multi(
  *    array.
  *
  *    The corresponding initial lowpass, bandpass, and highpass output values
- *    are put into `y_lp_0`, `y_bp_0`, and `y_hp_0` respectively, if they are
- *    not `NULL`.
+ *    are put into the `y_lp_0`, `y_bp_0`, and `y_hp_0` arrays, respectively, if
+ *    they are not `NULL`.
  *
  *    #### bw_svf_update_coeffs_ctrl()
  *  ```>>> */