sns: special cases for median-average filter

code/espurna/filters/MedianFilter.h

@@ -23,7 +23,7 @@ public:
     }
 
     double value() const override {
-        double sum { 0.0 };
+        double out { 0.0 };
 
         if (_values.size() > 2) {
             auto median = [](double previous, double current, double next) {
@@ -44,16 +44,21 @@ public:
                 return current;
             };
 
-            for (auto prev = _values.begin(); prev != (_values.end() - 2); ++prev) {
-                sum += median(*prev, *std::next(prev, 1), *std::next(prev, 2));
+            double counter = 0.0;
+            for (auto it = _values.begin(); it != (_values.end() - 2); ++it) {
+                out += median(*it, *std::next(it, 1), *std::next(it, 2));
+                counter += 1.0;
             }
 
-            sum /= (_values.size() - 2);
-        } else if (_values.size() > 0) {
-            sum = _values.front();
+            out /= counter;
+        } else if (_values.size() == 2) {
+            out = _values[0] + _values[1];
+            out /= 2.0;
+        } else if (_values.size() == 1) {
+            out = _values.front();
         }
 
-        return sum;
+        return out;
     }
 
     size_t capacity() const override {

code/test/unit/src/filters/filters.cpp

@@ -80,17 +80,39 @@ void test_median() {
     auto filter = MedianFilter();
     TEST_ASSERT_EQUAL(0, filter.capacity());
 
-    const double samples[] {1., 2., 2., 3., 4., 7., 9.};
-    filter.resize(std::size(samples));
+    const double one[] {4., 3., 5., 6., 2., 2., 3., 4., 7., 9.};
+    filter.resize(std::size(one));
 
     TEST_ASSERT_EQUAL(std::size(samples), filter.capacity());
     TEST_ASSERT_EQUAL_DOUBLE(0.0, filter.value());
 
-    for (const auto& sample : samples) {
+    for (const auto& sample : one) {
+        filter.update(sample);
+    }
+
+    TEST_ASSERT_EQUAL_DOUBLE(4.0, filter.value());
+
+    const double two[] {6., 6.1, 6.2, 6.3, 6.4, 6.5, 2.5, 4.5, 2.6, 2.5, 2.4};
+    filter.resize(std::size(two));
+
+    TEST_ASSERT_EQUAL_DOUBLE(9, filter.value());
+
+    for (const auto& sample : two) {
+        filter.update(sample);
+    }
+
+    TEST_ASSERT_EQUAL_DOUBLE(4.97, filter.value());
+
+    const double three[] {2.4, 2.4};
+    filter.resize(std::size(three));
+
+    TEST_ASSERT_EQUAL_DOUBLE(2.4, filter.value());
+
+    for (const auto& sample : three) {
         filter.update(sample);
     }
 
-    TEST_ASSERT_EQUAL_DOUBLE(3.6, filter.value());
+    TEST_ASSERT_EQUAL_DOUBLE(2.4, filter.value());
 }
 
 void test_moving_average() {