From cb91af4576aa5de46124b31241687e66b7474c3e Mon Sep 17 00:00:00 2001
From: Stefano D'Angelo <stefano.dangelo@orastron.com>
Date: Tue, 19 Sep 2023 14:35:38 +0200
Subject: [PATCH] finalized bw_{sr_reduce,bd_reduce} + examples

---
 TODO                                          |   1 +
 .../fx_bitcrush/src/bw_example_fx_bitcrush.c  |   7 +-
 examples/fx_bitcrush/vst3/Makefile            |   3 +
 examples/fxpp_bitcrush/vst3/Makefile          |   3 +
 include/bw_bd_reduce.h                        | 294 +++++++++--
 include/bw_sr_reduce.h                        | 465 ++++++++++++++++--
 6 files changed, 689 insertions(+), 84 deletions(-)

diff --git a/TODO b/TODO
index 3c8457c..bed6c55 100644
--- a/TODO
+++ b/TODO
@@ -78,6 +78,7 @@ code:
 * make all outs nullable?
 * make all reset state outs nullable (svf, phase_gen, ...)?
 * ring mod fx module?
+* bitcrusher module?
 
 build system:
 * make makefiles handle paths with spaces etc
diff --git a/examples/fx_bitcrush/src/bw_example_fx_bitcrush.c b/examples/fx_bitcrush/src/bw_example_fx_bitcrush.c
index 885df2e..27ef435 100644
--- a/examples/fx_bitcrush/src/bw_example_fx_bitcrush.c
+++ b/examples/fx_bitcrush/src/bw_example_fx_bitcrush.c
@@ -26,12 +26,13 @@ void bw_example_fx_bitcrush_init(bw_example_fx_bitcrush *instance) {
 }
 
 void bw_example_fx_bitcrush_set_sample_rate(bw_example_fx_bitcrush *instance, float sample_rate) {
-	(void)instance;
-	(void)sample_rate;
+	bw_sr_reduce_set_sample_rate(&instance->sr_reduce_coeffs, sample_rate);
+	bw_bd_reduce_set_sample_rate(&instance->bd_reduce_coeffs, sample_rate);
 }
 
 void bw_example_fx_bitcrush_reset(bw_example_fx_bitcrush *instance) {
-	bw_sr_reduce_reset_state(&instance->sr_reduce_coeffs, &instance->sr_reduce_state);
+	bw_sr_reduce_reset_coeffs(&instance->sr_reduce_coeffs);
+	bw_sr_reduce_reset_state(&instance->sr_reduce_coeffs, &instance->sr_reduce_state, 0.f);
 	bw_bd_reduce_reset_coeffs(&instance->bd_reduce_coeffs);
 }
 
diff --git a/examples/fx_bitcrush/vst3/Makefile b/examples/fx_bitcrush/vst3/Makefile
index 82de167..85be32b 100644
--- a/examples/fx_bitcrush/vst3/Makefile
+++ b/examples/fx_bitcrush/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fx_bitcrush
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_fx_bitcrush.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/fxpp_bitcrush/vst3/Makefile b/examples/fxpp_bitcrush/vst3/Makefile
index f2a1743..ce871a7 100644
--- a/examples/fxpp_bitcrush/vst3/Makefile
+++ b/examples/fxpp_bitcrush/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fxpp_bitcrush
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_fxpp_bitcrush.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_bd_reduce.h b/include/bw_bd_reduce.h
index cd0ce26..3ed8d37 100644
--- a/include/bw_bd_reduce.h
+++ b/include/bw_bd_reduce.h
@@ -33,6 +33,7 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
+ *          <li>Added <code>bw_bd_reduce_set_sample_rate()</code>.</li>
  *          <li><code>bw_bd_reduce_process()</code> and
  *              <code>bw_bd_reduce_process_multi()</code> now use
  *              <code>size_t</code> to count samples and channels.</li>
@@ -42,6 +43,8 @@
  *          <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>:
@@ -87,38 +90,56 @@ typedef struct bw_bd_reduce_coeffs bw_bd_reduce_coeffs;
  *
  *    #### bw_bd_reduce_init()
  *  ```>>> */
-static inline void bw_bd_reduce_init(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+static inline void bw_bd_reduce_init(
+	bw_bd_reduce_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Initializes input parameter values in `coeffs`.
  *
+ *    #### bw_bw_reduce_set_sample_rate()
+ *  ```>>> */
+static inline void bw_bd_reduce_set_sample_rate(
+	bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+	float                             sample_rate);
+/*! <<<```
+ *    Sets the `sample_rate` (Hz) value in `coeffs`.
+ *
  *    #### bw_bd_reduce_reset_coeffs()
  *  ```>>> */
-static inline void bw_bd_reduce_reset_coeffs(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+static inline void bw_bd_reduce_reset_coeffs(
+	bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
 /*! <<<```
  *    Resets coefficients in `coeffs` to assume their target values.
  *
  *    #### bw_bd_reduce_update_coeffs_ctrl()
  *  ```>>> */
-static inline void bw_bd_reduce_update_coeffs_ctrl(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+static inline void bw_bd_reduce_update_coeffs_ctrl(
+	bw_bd_reduce_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers control-rate update of coefficients in `coeffs`.
  *
  *    #### bw_bd_reduce_update_coeffs_audio()
  *  ```>>> */
-static inline void bw_bd_reduce_update_coeffs_audio(bw_bd_reduce_coeffs *BW_RESTRICT coeffs);
+static inline void bw_bd_reduce_update_coeffs_audio(
+	bw_bd_reduce_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers audio-rate update of coefficients in `coeffs`.
  *
  *    #### bw_bd_reduce_process1()
  *  ```>>> */
-static inline float bw_bd_reduce_process1(const bw_bd_reduce_coeffs *BW_RESTRICT coeffs, float x);
+static inline float bw_bd_reduce_process1(
+	const bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+	float                                   x);
 /*! <<<```
  *    Processes one input sample `x` using `coeffs`. Returns the corresponding
  *    output sample.
  *
  *    #### bw_bd_reduce_process()
  *  ```>>> */
-static inline void bw_bd_reduce_process(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, const float *x, float *y, size_t n_samples);
+static inline void bw_bd_reduce_process(
+	bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+	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
@@ -126,7 +147,12 @@ static inline void bw_bd_reduce_process(bw_bd_reduce_coeffs *BW_RESTRICT coeffs,
  *
  *    #### bw_bd_reduce_process_multi()
  *  ```>>> */
-static inline void bw_bd_reduce_process_multi(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, const float * const *x, float * const *y, size_t n_channels, size_t n_samples);
+static inline void bw_bd_reduce_process_multi(
+	bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+	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
@@ -134,11 +160,27 @@ static inline void bw_bd_reduce_process_multi(bw_bd_reduce_coeffs *BW_RESTRICT c
  *
  *    #### bw_bd_reduce_set_bit_depth()
  *  ```>>> */
-static inline void bw_bd_reduce_set_bit_depth(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, char value);
+static inline void bw_bd_reduce_set_bit_depth(
+	bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+	char                              value);
 /*! <<<```
- *    Sets the output bit depth `value` in `coeffs`. `value` must be strictly positive.
+ *    Sets the output bit depth `value` in `coeffs`.
+ *
+ *    Valid range: [`1`, `64`].
  *
  *    Default value: `16`.
+ *
+ *    #### bw_bd_reduce_coeffs_is_valid()
+ *  ```>>> */
+static inline char bw_bd_reduce_coeffs_is_valid(
+	const bw_bd_reduce_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_bd_reduce_coeffs`.
  *  }}} */
 
 #ifdef __cplusplus
@@ -156,27 +198,65 @@ static inline void bw_bd_reduce_set_bit_depth(bw_bd_reduce_coeffs *BW_RESTRICT c
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_bd_reduce_coeffs_state {
+	bw_bd_reduce_coeffs_state_invalid,
+	bw_bd_reduce_coeffs_state_init,
+	bw_bd_reduce_coeffs_state_set_sample_rate,
+	bw_bd_reduce_coeffs_state_reset_coeffs
+};
+#endif
+
 struct bw_bd_reduce_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_bd_reduce_coeffs_state	state;
+#endif
+
 	// Coefficients
-	float	ki;
-	float	k;
-	float	max;
+	float				ki;
+	float				k;
+	float				max;
 	
 	// Parameters
-	char	bit_depth;
-	char	bit_depth_prev;
+	char				bit_depth;
+	char				bit_depth_prev;
 };
 
-static inline void bw_bd_reduce_init(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_bd_reduce_init(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
 	coeffs->bit_depth = 16;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_bd_reduce_coeffs");
+	coeffs->state = bw_bd_reduce_coeffs_state_init;
+#endif
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_bd_reduce_coeffs_state_init);
 }
 
-static inline void bw_bd_reduce_reset_coeffs(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
-	coeffs->bit_depth_prev = 0;
-	bw_bd_reduce_update_coeffs_ctrl(coeffs);
+static inline void bw_bd_reduce_set_sample_rate(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+		float                             sample_rate) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
+
+	(void)coeffs;
+	(void)sample_rate;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_bd_reduce_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_bd_reduce_coeffs_state_set_sample_rate);
 }
 
-static inline void bw_bd_reduce_update_coeffs_ctrl(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_bd_reduce_do_update_coeffs_ctrl(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
 	if (coeffs->bit_depth_prev != coeffs->bit_depth) {
 		coeffs->k = bw_pow2f(coeffs->bit_depth - 1);
 		coeffs->ki = bw_rcpf(coeffs->k);
@@ -185,29 +265,144 @@ static inline void bw_bd_reduce_update_coeffs_ctrl(bw_bd_reduce_coeffs *BW_RESTR
 	}
 }
 
-static inline void bw_bd_reduce_update_coeffs_audio(bw_bd_reduce_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_bd_reduce_reset_coeffs(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_set_sample_rate);
+
+	coeffs->bit_depth_prev = 0;
+	bw_bd_reduce_do_update_coeffs_ctrl(coeffs);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_bd_reduce_coeffs_state_reset_coeffs;
+#endif
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_bd_reduce_coeffs_state_reset_coeffs);
+}
+
+static inline void bw_bd_reduce_update_coeffs_ctrl(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+
+	bw_bd_reduce_do_update_coeffs_ctrl(coeffs);
+
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+}
+
+static inline void bw_bd_reduce_update_coeffs_audio(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+
 	(void)coeffs;
 }
 
-static inline float bw_bd_reduce_process1(const bw_bd_reduce_coeffs *BW_RESTRICT coeffs, float x) {
-	return coeffs->ki * (bw_floorf(coeffs->k * bw_clipf(x, -coeffs->max, coeffs->max)) + 0.5f);
+static inline float bw_bd_reduce_process1(
+		const bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+		float                                   x) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(bw_is_finite(x));
+
+	const float y = coeffs->ki * (bw_floorf(coeffs->k * bw_clipf(x, -coeffs->max, coeffs->max)) + 0.5f);
+
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_bd_reduce_process(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, const float *x, float *y, size_t n_samples) {
+static inline void bw_bd_reduce_process(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+		const float *                     x,
+		float *                           y,
+		size_t                            n_samples) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+	BW_ASSERT(y != NULL);
+
 	bw_bd_reduce_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++)
 		y[i] = bw_bd_reduce_process1(coeffs, x[i]);
+
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
 }
 
-static inline void bw_bd_reduce_process_multi(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, const float * const *x, float * const *y, size_t n_channels, size_t n_samples) {
+static inline void bw_bd_reduce_process_multi(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+		const float * const *             x,
+		float * const *                   y,
+		size_t                            n_channels,
+		size_t                            n_samples) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT(y != NULL);
+
 	bw_bd_reduce_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++)
 		for (size_t j = 0; j < n_channels; j++)
 			y[j][i] = bw_bd_reduce_process1(coeffs, x[j][i]);
+
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_bd_reduce_set_bit_depth(bw_bd_reduce_coeffs *BW_RESTRICT coeffs, char value) {
+static inline void bw_bd_reduce_set_bit_depth(
+		bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
+		char                              value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_init);
+	BW_ASSERT(value >= 1 && value <= 64);
+
 	coeffs->bit_depth = value;
+
+	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_init);
+}
+
+static inline char bw_bd_reduce_coeffs_is_valid(
+		const bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->hash != bw_hash_sdbm("bw_bd_reduce_coeffs"))
+		return 0;
+	if (coeffs->state < bw_bd_reduce_coeffs_state_init || coeffs->state > bw_bd_reduce_coeffs_state_reset_coeffs)
+		return 0;
+#endif
+
+	if (coeffs->bit_depth < 1 || coeffs->bit_depth > 64)
+		return 0;
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs) {
+		if (coeffs->bit_depth_prev < 1 || coeffs->bit_depth_prev > 64)
+			return 0;
+		if (!bw_is_finite(coeffs->k) || coeffs->k <= 0.f)
+			return 0;
+		if (!bw_is_finite(coeffs->ki) || coeffs->ki <= 0.f)
+			return 0;
+		if (!bw_is_finite(coeffs->max) || coeffs->max < 0.5f || coeffs->max > 1.f)
+			return 0;
+	}
+#endif
+
+	return 1;
 }
 
 #ifdef __cplusplus
@@ -226,18 +421,24 @@ template<size_t N_CHANNELS>
 class BDReduce {
 public:
 	BDReduce();
-	
-	void reset();
-	void process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples);
-	void process(
-		const std::array<const float *, N_CHANNELS> x,
-		const std::array<float *, N_CHANNELS> y,
-		size_t nSamples);
 
-	void setBitDepth(char value);
+	void setSampleRate(
+		float sampleRate);
+
+	void reset();
+
+	void process(
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples);
+
+	void process(
+		std::array<const float *, N_CHANNELS> x,
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples);
+
+	void setBitDepth(
+		char value);
 /*! <<<...
  *  }
  *  ```
@@ -257,6 +458,12 @@ inline BDReduce<N_CHANNELS>::BDReduce() {
 	bw_bd_reduce_init(&coeffs);
 }
 
+template<size_t N_CHANNELS>
+inline void BDReduce<N_CHANNELS>::setSampleRate(
+		float sampleRate) {
+	bw_bd_reduce_set_sample_rate(&coeffs, sampleRate);
+}
+
 template<size_t N_CHANNELS>
 inline void BDReduce<N_CHANNELS>::reset() {
 	bw_bd_reduce_reset_coeffs(&coeffs);
@@ -264,22 +471,23 @@ inline void BDReduce<N_CHANNELS>::reset() {
 
 template<size_t N_CHANNELS>
 inline void BDReduce<N_CHANNELS>::process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples) {
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples) {
 	bw_bd_reduce_process_multi(&coeffs, x, y, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void BDReduce<N_CHANNELS>::process(
-		const std::array<const float *, N_CHANNELS> x,
-		const std::array<float *, N_CHANNELS> y,
-		size_t nSamples) {
+		std::array<const float *, N_CHANNELS> x,
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples) {
 	process(x.data(), y.data(), nSamples);
 }
 
 template<size_t N_CHANNELS>
-inline void BDReduce<N_CHANNELS>::setBitDepth(char value) {
+inline void BDReduce<N_CHANNELS>::setBitDepth(
+		char value) {
 	bw_bd_reduce_set_bit_depth(&coeffs, value);
 }
 
diff --git a/include/bw_sr_reduce.h b/include/bw_sr_reduce.h
index 0c2634c..4e41b49 100644
--- a/include/bw_sr_reduce.h
+++ b/include/bw_sr_reduce.h
@@ -33,8 +33,20 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
- *          <li><code>bw_sr_reduce_lim_process()</code> and
- *              <code>bw_sr_reduce_lim_process_multi()</code> now use
+ *          <li>Added <code>bw_sr_reduce_set_sample_rate()</code>,
+ *              <code>bw_sr_reduce_reset_coeffs()</code>,
+ *              <code>bw_sr_reduce_update_coeffs_ctrl()</code>, and
+ *              <code>bw_sr_reduce_update_coeffs_audio()</code>.</li>
+ *          <li>Added initial input value to
+ *              <code>bw_sr_reduce_reset_state()</code>.</li>
+ *          <li>Added <code>bw_sr_reduce_reset_state_multi()</code> and updated C++
+ *              API in this regard.</li>
+ *          <li>Now <code>bw_sr_reduce_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_sr_reduce_process()</code> and
+ *              <code>bw_sr_reduce_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>
@@ -42,6 +54,7 @@
  *          <li>Added overloaded C++ <code>process()</code> function taking
  *              C-style arrays as arguments.</li>
  *          <li>Removed usage of reserved identifiers.</li>
+ *          <li>Added debugging code.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>0.6.0</strong>:
@@ -93,26 +106,86 @@ typedef struct bw_sr_reduce_state bw_sr_reduce_state;
  *
  *    #### bw_sr_reduce_init()
  *  ```>>> */
-static inline void bw_sr_reduce_init(bw_sr_reduce_coeffs *BW_RESTRICT coeffs);
+static inline void bw_sr_reduce_init(
+	bw_sr_reduce_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Initializes input parameter values in `coeffs`.
  *
+ *    #### bw_sr_reduce_set_sample_rate()
+ *  ```>>> */
+static inline void bw_sr_reduce_set_sample_rate(
+	bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+	float                             sample_rate);
+/*! <<<```
+ *    Sets the `sample_rate` (Hz) value in `coeffs`.
+ *
+ *    #### bw_sr_reduce_reset_coeffs()
+ *  ```>>> */
+static inline void bw_sr_reduce_reset_coeffs(
+	bw_sr_reduce_coeffs * BW_RESTRICT coeffs);
+/*! <<<```
+ *    Resets coefficients in `coeffs` to assume their target values.
+ *
  *    #### 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);
+static inline float bw_sr_reduce_reset_state(
+	const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+	bw_sr_reduce_state * BW_RESTRICT        state,
+	float                                   x_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 input value `x_0`.
+ *
+ *    Returns the corresponding initial output value.
+ *
+ *    #### bw_sr_reduce_reset_state_multi()
+ *  ```>>> */
+static inline void bw_sr_reduce_reset_state_multi(
+	const bw_sr_reduce_coeffs * BW_RESTRICT              coeffs,
+	bw_sr_reduce_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 `NULL`.
+ *
+ *    #### bw_sr_reduce_update_coeffs_ctrl()
+ *  ```>>> */
+static inline void bw_sr_reduce_update_coeffs_ctrl(
+	bw_sr_reduce_coeffs * BW_RESTRICT coeffs);
+/*! <<<```
+ *    Triggers control-rate update of coefficients in `coeffs`.
+ *
+ *    #### bw_sr_reduce_update_coeffs_audio()
+ *  ```>>> */
+static inline void bw_sr_reduce_update_coeffs_audio(
+	bw_sr_reduce_coeffs * BW_RESTRICT coeffs);
+/*! <<<```
+ *    Triggers audio-rate update of coefficients in `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);
+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, size_t n_samples);
+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,
+	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 `coeffs` and
@@ -120,7 +193,13 @@ static inline void bw_sr_reduce_process(bw_sr_reduce_coeffs *BW_RESTRICT coeffs,
  *
  *    #### bw_sr_reduce_process_multi()
  *  ```>>> */
-static inline void bw_sr_reduce_process_multi(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x, float * const *y, size_t n_channels, size_t n_samples);
+static inline void bw_sr_reduce_process_multi(
+	bw_sr_reduce_coeffs * BW_RESTRICT                    coeffs,
+	bw_sr_reduce_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
@@ -129,13 +208,43 @@ static inline void bw_sr_reduce_process_multi(bw_sr_reduce_coeffs *BW_RESTRICT c
  *
  *    #### bw_sr_reduce_set_ratio()
  *  ```>>> */
-static inline void bw_sr_reduce_set_ratio(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, float value);
+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`.
+ *
+*    #### bw_sr_reduce_coeffs_is_valid()
+ *  ```>>> */
+static inline char bw_sr_reduce_coeffs_is_valid(
+	const bw_sr_reduce_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_sr_reduce_coeffs`.
+ *
+ *    #### bw_sr_reduce_state_is_valid()
+ *  ```>>> */
+static inline char bw_sr_reduce_state_is_valid(
+	const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+	const bw_sr_reduce_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_sr_reduce_state`.
  *  }}} */
 
 #ifdef __cplusplus
@@ -153,46 +262,271 @@ static inline void bw_sr_reduce_set_ratio(bw_sr_reduce_coeffs *BW_RESTRICT coeff
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_sr_reduce_coeffs_state {
+	bw_sr_reduce_coeffs_state_invalid,
+	bw_sr_reduce_coeffs_state_init,
+	bw_sr_reduce_coeffs_state_set_sample_rate,
+	bw_sr_reduce_coeffs_state_reset_coeffs
+};
+#endif
+
 struct bw_sr_reduce_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_sr_reduce_coeffs_state	state;
+	uint32_t			reset_id;
+#endif
+
 	// Parameters
-	float	ratio;
+	float				ratio;
 };
 
 struct bw_sr_reduce_state {
-	float	phase;
-	float	y_z1;
+#ifdef BW_DEBUG_DEEP
+	uint32_t	hash;
+	uint32_t	coeffs_reset_id;
+#endif
+
+	// States
+	float		phase;
+	float		y_z1;
 };
 
-static inline void bw_sr_reduce_init(bw_sr_reduce_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_sr_reduce_init(
+		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
 	coeffs->ratio = 1.f;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_sr_reduce_coeffs");
+	coeffs->state = bw_sr_reduce_coeffs_state_init;
+	coeffs->reset_id = coeffs->hash + 1;
+#endif
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_sr_reduce_coeffs_state_init);
 }
 
-static inline void bw_sr_reduce_reset_state(const bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state) {
+static inline void bw_sr_reduce_set_sample_rate(
+		bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+		float                             sample_rate) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
+
 	(void)coeffs;
-	state->phase = 1.f;
+	(void)sample_rate;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_sr_reduce_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_sr_reduce_coeffs_state_set_sample_rate);
 }
 
-static inline float bw_sr_reduce_process1(const bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT state, float x) {
+static inline void bw_sr_reduce_reset_coeffs(
+		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_set_sample_rate);
+
+	(void)coeffs;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_sr_reduce_coeffs_state_reset_coeffs;
+	coeffs->reset_id++;
+#endif
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_sr_reduce_coeffs_state_reset_coeffs);
+}
+
+static inline float bw_sr_reduce_reset_state(
+		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+		bw_sr_reduce_state * BW_RESTRICT        state,
+		float                                   x_0) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(bw_is_finite(x_0));
+
+	(void)coeffs;
+	state->y_z1 = x_0;
+	state->phase = 1.f;
+	const float y = x_0;
+
+#ifdef BW_DEBUG_DEEP
+	state->hash = bw_hash_sdbm("bw_sr_reduce_state");
+	state->coeffs_reset_id = coeffs->reset_id;
+#endif
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_sr_reduce_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
+}
+
+static inline void bw_sr_reduce_reset_state_multi(
+		const bw_sr_reduce_coeffs * BW_RESTRICT              coeffs,
+		bw_sr_reduce_state * BW_RESTRICT const * BW_RESTRICT state,
+		const float *                                        x_0,
+		float *                                              y_0,
+		size_t                                               n_channels) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(x_0 != NULL);
+
+	if (y_0 != NULL)
+		for (size_t i = 0; i < n_channels; i++)
+			y_0[i] = bw_sr_reduce_reset_state(coeffs, state[i], x_0[i]);
+	else
+		for (size_t i = 0; i < n_channels; i++)
+			bw_sr_reduce_reset_state(coeffs, state[i], x_0[i]);
+
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+}
+
+static inline void bw_sr_reduce_update_coeffs_ctrl(
+		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+
+	(void)coeffs;
+}
+
+static inline void bw_sr_reduce_update_coeffs_audio(
+		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+
+	(void)coeffs;
+}
+
+static inline float bw_sr_reduce_process1(
+		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+		bw_sr_reduce_state * BW_RESTRICT        state,
+		float                                   x) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(x));
+
 	state->phase += coeffs->ratio;
 	if (state->phase >= 1.f) {
 		state->y_z1 = x;
 		state->phase -= bw_floorf(state->phase);
 	}
-	return state->y_z1;
+	const float y = state->y_z1;
+
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_sr_reduce_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-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, size_t n_samples) {
+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,
+		size_t                            n_samples) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_state_is_valid(coeffs, state));
+	BW_ASSERT(x != NULL);
+	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+	BW_ASSERT(y != NULL);
+
 	for (size_t i = 0; i < n_samples; i++)
 		y[i] = bw_sr_reduce_process1(coeffs, state, x[i]);
+
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_sr_reduce_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
 }
 
-static inline void bw_sr_reduce_process_multi(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, bw_sr_reduce_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x, float * const *y, size_t n_channels, size_t n_samples) {
+static inline void bw_sr_reduce_process_multi(
+		bw_sr_reduce_coeffs * BW_RESTRICT                    coeffs,
+		bw_sr_reduce_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 != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT(y != NULL);
+
 	for (size_t i = 0; i < n_channels; i++)
 		bw_sr_reduce_process(coeffs, state[i], x[i], y[i], n_samples);
+
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_sr_reduce_set_ratio(bw_sr_reduce_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_sr_reduce_set_ratio(
+		bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+		float                             value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+	BW_ASSERT(value >= 0.f && value <= 1.f);
+
 	coeffs->ratio = value;
+
+	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_init);
+}
+
+static inline char bw_sr_reduce_coeffs_is_valid(
+		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->hash != bw_hash_sdbm("bw_sr_reduce_coeffs"))
+		return 0;
+	if (coeffs->state < bw_sr_reduce_coeffs_state_init || coeffs->state > bw_sr_reduce_coeffs_state_reset_coeffs)
+		return 0;
+#endif
+
+	return bw_is_finite(coeffs->ratio) && coeffs->ratio >= 0.f &&  coeffs->ratio <= 1.f;
+}
+
+static inline char bw_sr_reduce_state_is_valid(
+		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
+		const bw_sr_reduce_state * BW_RESTRICT  state) {
+	BW_ASSERT(state != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (state->hash != bw_hash_sdbm("bw_sr_reduce_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 && bw_is_finite(state->y_z1);
 }
 
 #ifdef __cplusplus
@@ -212,17 +546,37 @@ class SRReduce {
 public:
 	SRReduce();
 	
-	void reset();
+	void setSampleRate(
+		float sampleRate);
+
+	void reset(
+		float               x0 = 0.f,
+		float * BW_RESTRICT y0 = nullptr);
+
+	void reset(
+		float                                       x0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0);
+
+	void reset(
+		const float * x0,
+		float *       y0 = nullptr);
+
+	void reset(
+		std::array<float, N_CHANNELS>               x0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0 = nullptr);
+
 	void process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples);
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples);
+
 	void process(
 		std::array<const float *, N_CHANNELS> x,
-		std::array<float *, N_CHANNELS> y,
-		size_t nSamples);
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples);
 
-	void setRatio(float value);
+	void setRatio(
+		float value);
 /*! <<<...
  *  }
  *  ```
@@ -234,9 +588,9 @@ public:
  * change at any time in future versions. Please, do not use it directly. */
 
 private:
-	bw_sr_reduce_coeffs	 coeffs;
-	bw_sr_reduce_state	 states[N_CHANNELS];
-	bw_sr_reduce_state	*BW_RESTRICT statesP[N_CHANNELS];
+	bw_sr_reduce_coeffs			coeffs;
+	bw_sr_reduce_state			states[N_CHANNELS];
+	bw_sr_reduce_state * BW_RESTRICT	statesP[N_CHANNELS];
 };
 
 template<size_t N_CHANNELS>
@@ -247,24 +601,59 @@ inline SRReduce<N_CHANNELS>::SRReduce() {
 }
 
 template<size_t N_CHANNELS>
-inline void SRReduce<N_CHANNELS>::reset() {
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_sr_reduce_reset_state(&coeffs, states + i);
+inline void SRReduce<N_CHANNELS>::setSampleRate(
+		float sampleRate) {
+	bw_sr_reduce_set_sample_rate(&coeffs, sampleRate);
+}
+
+template<size_t N_CHANNELS>
+inline void SRReduce<N_CHANNELS>::reset(
+		float               x0,
+		float * BW_RESTRICT y0) {
+	bw_sr_reduce_reset_coeffs(&coeffs);
+	if (y0 != nullptr)
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			y0[i] = bw_sr_reduce_reset_state(&coeffs, states + i, x0);
+	else
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			bw_sr_reduce_reset_state(&coeffs, states + i, x0);
+}
+
+template<size_t N_CHANNELS>
+inline void SRReduce<N_CHANNELS>::reset(
+		float                                       x0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0) {
+	reset(x0, y0 != nullptr ? y0->data() : nullptr);
+}
+
+template<size_t N_CHANNELS>
+inline void SRReduce<N_CHANNELS>::reset(
+		const float * x0,
+		float *       y0) {
+	bw_sr_reduce_reset_coeffs(&coeffs);
+	bw_sr_reduce_reset_state_multi(&coeffs, statesP, x0, y0, N_CHANNELS);
+}
+
+template<size_t N_CHANNELS>
+inline void SRReduce<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);
 }
 
 template<size_t N_CHANNELS>
 inline void SRReduce<N_CHANNELS>::process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples) {
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples) {
 	bw_sr_reduce_process_multi(&coeffs, statesP, x, y, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void SRReduce<N_CHANNELS>::process(
 		std::array<const float *, N_CHANNELS> x,
-		std::array<float *, N_CHANNELS> y,
-		size_t nSamples) {
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples) {
 	process(x.data(), y.data(), nSamples);
 }