Fix gamma.h

Add tests for gamma decode

Author: rolandreichweinbmw

include/etl/gamma.h

@@ -63,7 +63,10 @@ namespace etl
     //*********************************
     TInput operator ()(TInput value) const
     {
-      return TInput(TInput(maximum * pow(double(value) / maximum, one_over_gamma)));
+      // Calculate intermediate result because rounding + optimization
+      // lead to wrong values when returning directly (test on i386)
+      const double result = maximum * pow(double(value) / maximum, one_over_gamma);
+      return TInput(result);
     }
 
   private:
@@ -95,7 +98,10 @@ namespace etl
     //*********************************
     TInput operator ()(TInput value) const
     {
-      return TInput(TInput(maximum * pow(double(value) / maximum, gamma)));
+      // Calculate intermediate result because rounding + optimization
+      // lead to wrong values when returning directly (test on i386)
+      const double result = maximum * pow(double(value) / maximum, gamma);
+      return TInput(result);
     }
 
   private:

test/test_gamma.cpp

@@ -41,6 +41,7 @@ namespace
   using IntGammaEncode    = etl::gamma_encode<int>;
   using DoubleGammaEncode = etl::gamma_encode<double>;
 
+  using IntGammaDecode    = etl::gamma_decode<int>;
   using DoubleGammaDecode = etl::gamma_decode<double>;
 
   struct Compare
@@ -62,6 +63,16 @@ namespace
     0, 0, 0, 1, 1, 2, 4, 5, 7, 9
   };
 
+  const std::array<int, Size> input1b =
+  {
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9
+  };
+
+  const std::array<int, Size> result1b =
+  {
+    0, 3, 4, 5, 6, 6, 7, 7, 8, 9
+  };
+
   std::array<int, Size> output1;
 
   //***********************************
@@ -100,6 +111,17 @@ namespace
       CHECK(isEqual);
     }
 
+    //*************************************************************************
+    TEST(test_int_gamma_decode)
+    {
+      IntGammaDecode gamma(0.5, 9);
+
+      std::transform(input1b.begin(), input1b.end(), output1.begin(), gamma);
+
+      bool isEqual = std::equal(output1.begin(), output1.end(), result1b.begin());
+      CHECK(isEqual);
+    }
+
     //*************************************************************************
     TEST(test_double_gamma_encode)
     {