Add DiodeRectifier

CMakeLists.txt

@@ -59,6 +59,7 @@ if(NOT CMAKE_CROSSCOMPILING)
             "lib/grit/audio/noise/airwindows_vinyl_dither_test.cpp"
             "lib/grit/audio/noise/dither_test.cpp"
             "lib/grit/audio/noise/white_noise_test.cpp"
+            "lib/grit/audio/waveshape/diode_rectifier_test.cpp"
             "lib/grit/audio/waveshape/full_wave_rectifier_test.cpp"
             "lib/grit/audio/waveshape/half_wave_rectifier_test.cpp"
             "lib/grit/audio/waveshape/hard_clipper_test.cpp"

lib/grit/audio/waveshape.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <grit/audio/waveshape/diode_rectifier.hpp>
 #include <grit/audio/waveshape/full_wave_rectifier.hpp>
 #include <grit/audio/waveshape/half_wave_rectifier.hpp>
 #include <grit/audio/waveshape/hard_clipper.hpp>

lib/grit/audio/waveshape/diode_rectifier.hpp

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <grit/audio/waveshape/wave_shaper.hpp>
+#include <grit/audio/waveshape/wave_shaper_adaa1.hpp>
+
+#include <etl/cmath.hpp>
+#include <etl/concepts.hpp>
+
+namespace grit {
+
+template<etl::floating_point Float>
+struct DiodeRectifierNonlinearity
+{
+    constexpr DiodeRectifierNonlinearity() = default;
+
+    [[nodiscard]] constexpr auto operator()(Float x) const -> Float { return f(x); }
+
+    [[nodiscard]] static constexpr auto f(Float x) -> Float
+    {
+        return Float(0.2) * etl::exp(Float(1.79) * x) - Float(0.2);
+    }
+
+    [[nodiscard]] static constexpr auto ad1(Float x) -> Float
+    {
+        return Float(-0.2) * x + Float(0.111731843575419) * etl::exp(Float(1.79) * x);
+    }
+};
+
+template<etl::floating_point Float>
+using DiodeRectifier = WaveShaper<Float, DiodeRectifierNonlinearity<Float>>;
+
+template<etl::floating_point Float>
+using DiodeRectifierADAA1 = WaveShaperADAA1<Float, DiodeRectifierNonlinearity<Float>>;
+
+}  // namespace grit

lib/grit/audio/waveshape/diode_rectifier_test.cpp

@@ -0,0 +1,29 @@
+#include "diode_rectifier.hpp"
+
+#include <catch2/catch_approx.hpp>
+#include <catch2/catch_template_test_macros.hpp>
+
+TEMPLATE_TEST_CASE("grit/audio/waveshape: DiodeRectifier", "", double)
+{
+    using Float = TestType;
+
+    auto shaper = grit::DiodeRectifier<Float>{};
+    STATIC_REQUIRE(etl::is_empty_v<grit::DiodeRectifier<Float>>);
+
+    REQUIRE(shaper(Float(-2.0)) == Catch::Approx(-0.1944248603));
+    REQUIRE(shaper(Float(-1.5)) == Catch::Approx(-0.1863557612));
+    REQUIRE(shaper(Float(+0.0)) == Catch::Approx(+0.0));
+    REQUIRE(shaper(Float(+1.0)) == Catch::Approx(+0.9978904933));
+}
+
+TEMPLATE_TEST_CASE("grit/audio/waveshape: DiodeRectifierADAA1", "", float, double)
+{
+    using Float = TestType;
+
+    auto shaper = grit::DiodeRectifierADAA1<Float>{};
+    REQUIRE(shaper(Float(-2.0)) < Float(0));
+    REQUIRE(shaper(Float(-2.0)) == Catch::Approx(-0.1944248603));
+
+    REQUIRE(shaper(Float(-1.5)) < Float(0));
+    REQUIRE(shaper(Float(-1.5)) == Catch::Approx(-0.1863557612));
+}