From a4b2defa178b10d277246ce5262704f1b0e2cff2 Mon Sep 17 00:00:00 2001
From: AkiyukiOkayasu <akiyuki.okayasu@gmail.com>
Date: Fri, 10 Mar 2023 15:18:08 +0900
Subject: [PATCH] Add diode modeling function

---
 include/ame.hpp         |  1 +
 include/ame_Circuit.hpp | 28 ++++++++++++++++++++++++++++
 test/test.cpp           | 14 ++++++++++++++
 3 files changed, 43 insertions(+)
 create mode 100644 include/ame_Circuit.hpp

diff --git a/include/ame.hpp b/include/ame.hpp
index 16955f2..86a2efc 100644
--- a/include/ame.hpp
+++ b/include/ame.hpp
@@ -29,6 +29,7 @@
 #include "ame_Ambisonics.hpp"
 #include "ame_AudioBuffer.hpp"
 #include "ame_Biquad.hpp"
+#include "ame_Circuit.hpp"
 #include "ame_Conversion.hpp"
 #include "ame_DcBlock.hpp"
 #include "ame_Delay.hpp"
diff --git a/include/ame_Circuit.hpp b/include/ame_Circuit.hpp
new file mode 100644
index 0000000..84506ec
--- /dev/null
+++ b/include/ame_Circuit.hpp
@@ -0,0 +1,28 @@
+/** 
+    Analog circuit modelings
+    @file ame_Circuit.hpp
+    @author Akiyuki Okayasu (akiyuki.okayasu@gmail.com)
+    @copyright Copyright (c) 2021 - Akiyuki Okayasu
+    
+    AME is released under the MIT license.
+*/
+
+#pragma once
+
+#include <concepts>
+
+namespace ame
+{
+/** diode modeling.
+    https://jatinchowdhury18.medium.com/complex-nonlinearities-epsiode-2-harmonic-exciter-cd883d888a43
+
+    @param x 
+    @return FloatType
+    @note When the input is 1.0, the output is larger than 1.0    
+*/
+template <std::floating_point FloatType>
+inline FloatType diode (FloatType x)
+{
+    return static_cast<FloatType> (0.2) * (std::exp (x * static_cast<FloatType> (0.05 / 0.0259)) - static_cast<FloatType> (1.0));
+}
+} // namespace ame
\ No newline at end of file
diff --git a/test/test.cpp b/test/test.cpp
index ece5e72..7c22ead 100644
--- a/test/test.cpp
+++ b/test/test.cpp
@@ -9,6 +9,20 @@
 
 using doctest::Approx;
 
+TEST_CASE ("Circuit modeling")
+{
+    SUBCASE ("Diode")
+    {
+        CHECK_GT (ame::diode (1.0f), 1.0);
+        CHECK_EQ (ame::diode (0.5f), Approx (0.325089f));
+        CHECK_EQ (ame::diode (0.1f), Approx (0.042589f));
+        CHECK_EQ (ame::diode (0.0f), Approx (0.0f));
+        CHECK_EQ (ame::diode (-0.25f), Approx (-0.076568f));
+        CHECK_EQ (ame::diode (-0.8f), Approx (-0.157312f));
+        CHECK_GT (0.0f, ame::diode (-1.0f));
+    }
+}
+
 TEST_CASE ("Radian / Degree")
 {
     CHECK_EQ (ame::rad2deg (0.0f), Approx (0.0f));