Refactor ExponentialMovingAverageFilter to use a templated input type.

This requires a pull request be merged to ArduinoSTL before it will
build on AVR-based platforms (e.g. UNO).
mike-matera/ArduinoSTL#52

Author: ademuri

src/exponential-moving-average-filter.h

@@ -3,6 +3,8 @@
 
 #include "filter.h"
 
+#include <type_traits>
+
 // An exponential moving average filter. This uses only integer (32-bit) math.
 // This supports up to 24-bit inputs.
 //
@@ -13,47 +15,54 @@
 //
 // An alpha of 255 means that the filter returns the current value of the input.
 // An alpha of 0 means the filtered value changes very slowly.
-template <typename OutputType>
-class ExponentialMovingAverageFilter : public Filter<uint32_t, OutputType> {
-  using Filter<uint32_t, OutputType>::sensor_value_;
+template <typename InputType, typename OutputType>
+class ExponentialMovingAverageFilter : public Filter<InputType, OutputType> {
+  using Filter<InputType, OutputType>::sensor_value_;
 
  public:
-  ExponentialMovingAverageFilter(uint32_t (*const ReadFromSensor)(),
-                                 uint8_t alpha);
-  ExponentialMovingAverageFilter(uint32_t (*const ReadFromSensor)(),
-                                 uint8_t alpha,
-                                 OutputType (*Convert)(uint32_t input));
+  ExponentialMovingAverageFilter(InputType (*const ReadFromSensor)(),
+                                 InputType alpha);
+  ExponentialMovingAverageFilter(InputType (*const ReadFromSensor)(),
+                                 InputType alpha,
+                                 OutputType (*Convert)(InputType input));
 
  protected:
-  uint32_t DoRun() override;
+  InputType DoRun() override;
 
  private:
-  uint32_t average_ = 0;
+  InputType average_ = 0;
 
-  const uint8_t alpha_;
+  const InputType alpha_;
 };
 
-template <typename OutputType>
-ExponentialMovingAverageFilter<OutputType>::ExponentialMovingAverageFilter(
-    uint32_t (*const ReadFromSensor)(), uint8_t alpha)
-    : Filter<uint32_t, OutputType>(ReadFromSensor), alpha_(alpha) {}
-
-template <typename OutputType>
-ExponentialMovingAverageFilter<OutputType>::ExponentialMovingAverageFilter(
-    uint32_t (*const ReadFromSensor)(), uint8_t alpha,
-    OutputType (*Convert)(uint32_t input))
-    : Filter<uint32_t, OutputType>(ReadFromSensor, Convert), alpha_(alpha) {}
-
-template <typename OutputType>
-uint32_t ExponentialMovingAverageFilter<OutputType>::DoRun() {
-  uint32_t old_average = average_;
-  average_ = (sensor_value_ * (alpha_ + 1) + (average_ * (255 - alpha_))) / 256;
-  if (old_average == average_ && sensor_value_ != average_) {
-    if (sensor_value_ > average_) {
-      average_++;
-    } else if (sensor_value_ < average_) {
-      average_--;
+template <typename InputType, typename OutputType>
+ExponentialMovingAverageFilter<InputType, OutputType>::
+    ExponentialMovingAverageFilter(InputType (*const ReadFromSensor)(),
+                                   InputType alpha)
+    : Filter<InputType, OutputType>(ReadFromSensor), alpha_(alpha) {}
+
+template <typename InputType, typename OutputType>
+ExponentialMovingAverageFilter<InputType, OutputType>::
+    ExponentialMovingAverageFilter(InputType (*const ReadFromSensor)(),
+                                   InputType alpha,
+                                   OutputType (*Convert)(InputType input))
+    : Filter<InputType, OutputType>(ReadFromSensor, Convert), alpha_(alpha) {}
+
+template <typename InputType, typename OutputType>
+InputType ExponentialMovingAverageFilter<InputType, OutputType>::DoRun() {
+  InputType old_average = average_;
+  if (std::is_integral<InputType>::value) {
+    average_ =
+        (sensor_value_ * (alpha_ + 1) + (average_ * (255 - alpha_))) / 256;
+    if (old_average == average_ && sensor_value_ != average_) {
+      if (sensor_value_ > average_) {
+        average_++;
+      } else if (sensor_value_ < average_) {
+        average_--;
+      }
     }
+  } else {
+    average_ = (sensor_value_ * (alpha_) + (average_ * (1.0 - alpha_)));
   }
   return average_;
 }

test/exponential-moving-average-filter-float-test.cpp

@@ -0,0 +1,42 @@
+#include "gtest/gtest.h"
+
+#include <cstdio>
+#include "../src/exponential-moving-average-filter.h"
+#include "run-data-test.h"
+
+namespace exponential_moving_average_filter_test {
+
+TEST(ExponentialMovingAverageFloatFilter, alpha_half) {
+  ExponentialMovingAverageFilter<float, float> *filter = new ExponentialMovingAverageFilter<float, float>(floatRead, 0.5);
+  std::vector<InputOutput<float, float>> data = {
+    {0, 10, 0},
+    {1.0, 100, 0.4, 1.0},
+    {1.0, 100, 1.0},
+    {0, 100, 0, 0.6},
+    {0, 100, 0, 0.001},
+  };
+  RunDataTest(filter, data, setFloatRead);
+}
+
+TEST(ExponentialMovingAverageFloatFilter, alpha_full) {
+  ExponentialMovingAverageFilter<float, float> *filter = new ExponentialMovingAverageFilter<float, float>(floatRead, 1.0);
+  std::vector<InputOutput<float, float>> data = {
+    {0, 10, 0},
+    {10.0, 100, 10.0},
+    {0, 100, 0},
+  };
+  RunDataTest(filter, data, setFloatRead);
+}
+
+TEST(ExponentialMovingAverageFloatFilter, alpha_low) {
+  ExponentialMovingAverageFilter<float, float> *filter = new ExponentialMovingAverageFilter<float, float>(floatRead, 0.001);
+  std::vector<InputOutput<float, float>> data = {
+    {0, 10, 0},
+    {1.0, 500, 0, 0.5},
+    {1.0, 5000, 0, 1.0},
+    {1.0, 100, 0.99, 1.0},
+  };
+  RunDataTest(filter, data, setFloatRead);
+}
+
+}

test/exponential-moving-average-filter-test.cpp

@@ -7,7 +7,7 @@
 namespace exponential_moving_average_filter_test {
 
 TEST(ExponentialMovingAverageFilter, alpha_half) {
-  ExponentialMovingAverageFilter<uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 128);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 128);
   std::vector<InputOutput<uint32_t, uint32_t>> data = {
     {0, 10, 0},
     {1024, 100, 4, 1024},
@@ -19,7 +19,7 @@ TEST(ExponentialMovingAverageFilter, alpha_half) {
 }
 
 TEST(ExponentialMovingAverageFilter, alpha_full) {
-  ExponentialMovingAverageFilter<uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 255);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 255);
   std::vector<InputOutput<uint32_t, uint32_t>> data = {
     {0, 10, 0},
     {1024, 100, 1024},
@@ -29,7 +29,7 @@ TEST(ExponentialMovingAverageFilter, alpha_full) {
 }
 
 TEST(ExponentialMovingAverageFilter, alpha_low) {
-  ExponentialMovingAverageFilter<uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 0);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 0);
   std::vector<InputOutput<uint32_t, uint32_t>> data = {
     {0, 10, 0},
     {1024, 10, 4, 50},
@@ -43,7 +43,7 @@ TEST(ExponentialMovingAverageFilter, alpha_low) {
 }
 
 TEST(ExponentialMovingAverageFilter, impulse) {
-  ExponentialMovingAverageFilter<uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 127);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 127);
   std::vector<InputOutput<uint32_t, uint32_t>> data = {
     {0, 10, 0},
     {1024, 1, 512},
@@ -77,7 +77,7 @@ float analogInToVoltage(uint32_t analogIn) {
 }
 
 TEST(ExponentialMovingAverageFilter, convert) {
-  ExponentialMovingAverageFilter<float> *filter = new ExponentialMovingAverageFilter<float>(analogRead, 127, analogInToVoltage);
+  ExponentialMovingAverageFilter<uint32_t, float> *filter = new ExponentialMovingAverageFilter<uint32_t, float>(analogRead, 127, analogInToVoltage);
   std::vector<InputOutput<uint32_t, float>> data = {
     {0, 10, 0.0},
     {1023, 100, 0.0, 3.3},
@@ -90,7 +90,7 @@ TEST(ExponentialMovingAverageFilter, filter_range) {
   // Tests that the filter supports 24-bit filters without overflow.
   // Note: 2 ^ 24 = 16777216
 
-  ExponentialMovingAverageFilter<uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 127);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *filter = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 127);
   std::vector<InputOutput<uint32_t, uint32_t>> data = {
     {16777215, 500, 0, 16777215},
     {16777215, 100, 16777215},

test/filter-test.cpp

@@ -8,7 +8,7 @@ namespace filter_test {
 
 TEST(Filter, SetMinRunInterval_default) {
   // Filter that returns the sensor value immediately
-  ExponentialMovingAverageFilter<uint32_t> *input = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 255);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *input = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 255);
   std::vector<InputOutput<uint32_t, uint32_t>> data = {
     {1, 1, 1},
     {2, 1, 2},
@@ -21,7 +21,7 @@ TEST(Filter, SetMinRunInterval_default) {
 
 TEST(Filter, SetMinRunInterval_10) {
   // Filter that returns the sensor value immediately
-  ExponentialMovingAverageFilter<uint32_t> *input = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 255);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *input = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 255);
   input->SetMinRunInterval(10);
   std::vector<InputOutput<uint32_t, uint32_t>> data = {
     {1, 1, 1},
@@ -36,7 +36,7 @@ TEST(Filter, SetMinRunInterval_10) {
 }
 
 TEST(Filter, SetMinRunInterval_updates) {
-  ExponentialMovingAverageFilter<uint32_t> *input = new ExponentialMovingAverageFilter<uint32_t>(analogRead, 255);
+  ExponentialMovingAverageFilter<uint32_t, uint32_t> *input = new ExponentialMovingAverageFilter<uint32_t, uint32_t>(analogRead, 255);
   input->SetMinRunInterval(10);
   input->SetMillis(0);
   analogReadValue = 1;