Cherry pick the OPF refactor from the smoothers

benchmarks/BM_filterModulation.cpp

@@ -8,6 +8,7 @@
 #include "OnePoleFilter.h"
 #include "SfzFilter.h"
 #include "ScopedFTZ.h"
+#include "SfzHelpers.h"
 #include <benchmark/benchmark.h>
 #include <random>
 #include <numeric>
@@ -57,7 +58,7 @@ BENCHMARK_DEFINE_F(FilterFixture, OnePole_VA)(benchmark::State& state) {
         const auto sentinel = cutoff.data() + blockSize;
         while (cutoffPtr < sentinel)
         {
-            const auto gain = sfz::OnePoleFilter<float>::normalizedGain(*cutoffPtr, sampleRate);
+            const auto gain = sfz::vaGain(*cutoffPtr, sampleRate);
             filter.setGain(gain);
             filter.processLowpass({ inputPtr, step }, { outputPtr, step } );
             cutoffPtr += step;

src/sfizz/MathHelpers.h

@@ -340,6 +340,66 @@ bool isValidAudio(absl::Span<Type> span)
     return true;
 }
 
+/**
+ * @brief Finds the minimum size of 2 spans
+ *
+ * @tparam T
+ * @tparam U
+ * @param span1
+ * @param span2
+ * @return constexpr size_t
+ */
+template <class T, class U>
+constexpr size_t minSpanSize(absl::Span<T>& span1, absl::Span<U>& span2)
+{
+    return min(span1.size(), span2.size());
+}
+
+/**
+ * @brief Finds the minimum size of a list of spans.
+ *
+ * @tparam T
+ * @tparam Others
+ * @param first
+ * @param others
+ * @return constexpr size_t
+ */
+template <class T, class... Others>
+constexpr size_t minSpanSize(absl::Span<T>& first, Others... others)
+{
+    return min(first.size(), minSpanSize(others...));
+}
+
+template <class T>
+constexpr bool _checkSpanSizes(size_t size, absl::Span<T>& span1)
+{
+    return span1.size() == size;
+}
+
+template <class T, class... Others>
+constexpr bool _checkSpanSizes(size_t size, absl::Span<T>& span1, Others... others)
+{
+    return span1.size() == size && _checkSpanSizes(size, others...);
+}
+
+/**
+ * @brief Check that all spans of a compile time list have the same size
+ *
+ * @tparam T
+ * @tparam Others
+ * @param first
+ * @param others
+ * @return constexpr size_t
+ */
+template <class T, class... Others>
+constexpr bool checkSpanSizes(const absl::Span<T>& span1, Others... others)
+{
+    return _checkSpanSizes(span1.size(), others...);
+}
+
+#define CHECK_SPAN_SIZES(...) ASSERT(checkSpanSizes(__VA_ARGS__))
+
+
 class ScopedRoundingMode {
 public:
     ScopedRoundingMode() = delete;

src/sfizz/OnePoleFilter.h

@@ -6,12 +6,14 @@
 
 #pragma once
 #include "Config.h"
+#include "Debug.h"
 #include "MathHelpers.h"
+#include "Macros.h"
 #include <absl/types/span.h>
 #include <cmath>
 
-namespace sfz
-{
+namespace sfz {
+
 /**
  * @brief An implementation of a one pole filter. This is a scalar
  * implementation.
@@ -22,108 +24,82 @@ template <class Type = float>
 class OnePoleFilter {
 public:
     OnePoleFilter() = default;
-    // Normalized cutoff with respect to the sampling rate
-    template <class C>
-    static Type normalizedGain(Type cutoff, C sampleRate)
-    {
-        return std::tan(cutoff / static_cast<Type>(sampleRate) * pi<float>());
-    }
-
-    OnePoleFilter(Type gain)
-    {
-        setGain(gain);
-    }
 
     void setGain(Type gain)
     {
-        this->gain = gain;
         G = gain / (1 + gain);
     }
 
-    Type getGain() const { return gain; }
-
-    size_t processLowpass(absl::Span<const Type> input, absl::Span<Type> lowpass)
+    void processLowpass(absl::Span<const Type> input, absl::Span<Type> output)
     {
-        auto in = input.begin();
-        auto out = lowpass.begin();
-        auto size = std::min(input.size(), lowpass.size());
-        auto sentinel = in + size;
-        while (in < sentinel) {
-            oneLowpass(in, out);
-            in++;
-            out++;
-        }
-        return size;
+        CHECK_SPAN_SIZES(input, output);
+        processLowpass(input.data(), output.data(), minSpanSize(input, output));
     }
 
-    size_t processHighpass(absl::Span<const Type> input, absl::Span<Type> highpass)
+    void processHighpass(absl::Span<const Type> input, absl::Span<Type> output)
     {
-        auto in = input.begin();
-        auto out = highpass.begin();
-        auto size = std::min(input.size(), highpass.size());
-        auto sentinel = in + size;
-        while (in < sentinel) {
-            oneHighpass(in, out);
-            in++;
-            out++;
-        }
-        return size;
+        CHECK_SPAN_SIZES(input, output);
+        processHighpass(input.data(), output.data(), minSpanSize(input, output));
     }
 
-    size_t processLowpassVariableGain(absl::Span<const Type> input, absl::Span<Type> lowpass, absl::Span<const Type> gain)
+    void processLowpass(absl::Span<const Type> input, absl::Span<Type> output, absl::Span<const Type> gain)
     {
-        auto in = input.begin();
-        auto out = lowpass.begin();
-        auto g = gain.begin();
-        auto size = min(input.size(), lowpass.size(), gain.size());
-        auto sentinel = in + size;
-        while (in < sentinel) {
-            setGain(*g);
-            oneLowpass(in, out);
-            in++;
-            out++;
-            g++;
-        }
-        return size;
+        CHECK_SPAN_SIZES(input, output, gain);
+        processLowpass(input.data(), output.data(), gain.data(), minSpanSize(input, output, gain));
     }
 
-    size_t processHighpassVariableGain(absl::Span<const Type> input, absl::Span<Type> highpass, absl::Span<const Type> gain)
+    void processHighpass(absl::Span<const Type> input, absl::Span<Type> output, absl::Span<const Type> gain)
     {
-        auto in = input.begin();
-        auto out = highpass.begin();
-        auto g = gain.begin();
-        auto size = min(input.size(), highpass.size(), gain.size());
-        auto sentinel = in + size;
-        while (in < sentinel) {
-            setGain(*g);
-            oneHighpass(in, out);
-            in++;
-            out++;
-            g++;
-        }
-        return size;
+        CHECK_SPAN_SIZES(input, output, gain);
+        processHighpass(input.data(), output.data(), gain.data(), minSpanSize(input, output, gain));
     }
 
-    void reset() { state = 0.0; }
+    void processLowpass(const Type* input, Type* output, unsigned size)
+    {
+        for (unsigned i = 0; i < size; ++i) {
+            const Type intermediate = G * (input[i] - state);
+            output[i] = intermediate + state;
+            state = output[i] + intermediate;
+        }
+    }
+
+    void processHighpass(const Type* input, Type* output, unsigned size)
+    {
+        for (unsigned i = 0; i < size; ++i) {
+            const Type intermediate = G * (input[i] - state);
+            output[i] = input[i] - intermediate - state;
+            state += 2 * intermediate;
+        }
+    }
+
+    void processLowpass(const Type* input, Type* output, const Type* gain, unsigned size)
+    {
+        for (unsigned i = 0; i < size; ++i) {
+            setGain(gain[i]);
+            const Type intermediate = G * (input[i] - state);
+            output[i] = intermediate + state;
+            state = output[i] + intermediate;
+        }
+    }
+
+    void processHighpass(const Type* input, Type* output, const Type* gain, unsigned size)
+    {
+        for (unsigned i = 0; i < size; ++i) {
+            setGain(gain[i]);
+            const Type intermediate = G * (input[i] - state);
+            output[i] = input[i] - intermediate - state;
+            state += 2 * intermediate;
+        }
+    }
+
+    void reset(Type value = 0.0)
+    {
+        state = value;
+    }
 
 private:
     Type state { 0.0 };
-    Type gain { 0.25 };
-    Type intermediate { 0.0 };
-    Type G { gain / (1 + gain) };
-
-    inline void oneLowpass(const Type* in, Type* out)
-    {
-        intermediate = G * (*in - state);
-        *out = intermediate + state;
-        state = *out + intermediate;
-    }
-
-    inline void oneHighpass(const Type* in, Type* out)
-    {
-        intermediate = G * (*in - state);
-        *out = *in - intermediate - state;
-        state += 2 * intermediate;
-    }
+    Type G { 0.5 };
 };
+
 }

src/sfizz/SfzHelpers.h

@@ -204,6 +204,12 @@ namespace literals {
  */
 absl::optional<uint8_t> readNoteValue(const absl::string_view& value);
 
+template <class Type>
+inline CXX14_CONSTEXPR Type vaGain(Type cutoff, Type sampleRate)
+{
+    return std::tan(cutoff / sampleRate * pi<Type>());
+}
+
 /**
  * @brief From a source view, find the next sfz header and its members and
  *          return them, while updating the source by removing this header

tests/OnePoleFilterT.cpp

@@ -40,12 +40,13 @@ void testFilter(const std::array<Type, N>& input, const std::array<Type, N>& exp
     std::array<Type, N> gains;
     std::fill(gains.begin(), gains.end(), gain);
 
-    sfz::OnePoleFilter<Type> filter { gain };
+    sfz::OnePoleFilter<Type> filter;
+    filter.setGain(gain);
     filter.processLowpass(input, outputSpan);
     REQUIRE(approxEqual(output, expectedLow));
 
     filter.reset();
-    filter.processLowpassVariableGain(input, outputSpan, gains);
+    filter.processLowpass(input, outputSpan, gains);
     REQUIRE(approxEqual(output, expectedLow));
 
     filter.reset();
@@ -53,7 +54,7 @@ void testFilter(const std::array<Type, N>& input, const std::array<Type, N>& exp
     REQUIRE(approxEqual(output, expectedHigh));
 
     filter.reset();
-    filter.processHighpassVariableGain(input, outputSpan, gains);
+    filter.processHighpass(input, outputSpan, gains);
     REQUIRE(approxEqual(output, expectedHigh));
 }