simplex: fix a bug in the modulo operator. lol. and add unit tests.

src/lol/math/simplex_interpolator.h

@@ -83,7 +83,8 @@ protected:
     inline int Mod(int value, int index) const
     {
         int const dim = this->m_samples.GetSize()[index];
-        return value % dim + (value >= 0 ? 0 : dim);
+        int const ret = value % dim;
+        return ret >= 0 ? ret : ret + dim;
     }
 
     inline void GetReference(vec_t<int, N> & floor_point, vec_t<T, N> & decimal_point, int & sign) const

src/t/math/simplex_interpolator.cpp

@@ -23,6 +23,31 @@ lolunit_declare_fixture(SimplexInterpolatorTest)
 
     void TearDown() {}
 
+    lolunit_declare_test(GridPoints2D1x1)
+    {
+        simplex_interpolator<2> s({{1.f}});
+        float val;
+
+        val = s.Interp(GridPoint2D(-1, -1));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(0, -1));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(1, -1));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(-1, 0));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(0, 0));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(1, 0));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(-1, 1));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(0, 1));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+        val = s.Interp(GridPoint2D(1, 1));
+        lolunit_assert_doubles_equal(1.f, val, 1e-5f);
+    }
+
     lolunit_declare_test(GridPoints2D2x2)
     {
         simplex_interpolator<2> s({{1.f, 1.f}, {1.f, 2.f}});