simplex_interpolator: bug fix on negative values.

src/lol/math/simplex_interpolator.h

@@ -117,7 +117,7 @@ protected:
     {
         // Finding floor point index
         for (int i = 0 ; i < N ; ++i)
-            floor_point[i] = (int) simplex_position[i];
+            floor_point[i] = ((int) simplex_position[i]) - (simplex_position[i] < 0 ? 1 : 0);
 
         // Extracting decimal part from simplex sample
         for (int i = 0 ; i < N ; ++i)

src/t/math/simplex_interpolator.cpp

@@ -226,9 +226,9 @@ lolunit_declare_fixture(SimplexInterpolatorTest)
         s.SetGradients(gradients);
 
         std::cout << std::endl;
-        for (int i = 0 ; i < 32 ; ++i)
+        for (int i = -64 ; i < 64 ; ++i)
         {
-            for (int j = 0 ; j < 32 ; ++j)
+            for (int j = -64 ; j < 64 ; ++j)
             {
                 std::cout << s.Interp(vec_t<float, 2>({i * 0.1f, j * 0.1f})) << ", ";
             }