More precise double Math constants.

Double has 15-17 significant decimal digits precision, extended
the constant to have 15 decimal digits. On the other hand, float has
only 6-9 digits, so there is no need to have more than 9.

Added just-to-be-sure test for sqrt* constants.

src/Math/Math.h

@@ -50,14 +50,14 @@ template<class T> struct Constants {
 
 #ifndef DOXYGEN_GENERATING_OUTPUT
 template<> struct Constants<double> {
-    static inline constexpr double pi() { return 3.14159265359; }
-    static inline constexpr double sqrt2() { return 1.41421356237; }
-    static inline constexpr double sqrt3() { return 1.73205080757; }
+    static inline constexpr double pi()    { return 3.141592653589793; }
+    static inline constexpr double sqrt2() { return 1.414213562373095; }
+    static inline constexpr double sqrt3() { return 1.732050807568877; }
 };
 template<> struct Constants<float> {
-    static inline constexpr float pi() { return 3.14159265359f; }
-    static inline constexpr float sqrt2() { return 1.41421356237f; }
-    static inline constexpr float sqrt3() { return 1.73205080757f; }
+    static inline constexpr float pi()    { return 3.141592654f; }
+    static inline constexpr float sqrt2() { return 1.414213562f; }
+    static inline constexpr float sqrt3() { return 1.732050808f; }
 };
 
 namespace Implementation {

src/Math/Test/MathTest.cpp

@@ -24,13 +24,22 @@ CORRADE_TEST_MAIN(Magnum::Math::Test::MathTest)
 namespace Magnum { namespace Math { namespace Test {
 
 MathTest::MathTest() {
-    addTests(&MathTest::degrad,
+    addTests(&MathTest::constants,
+             &MathTest::degrad,
              &MathTest::normalize,
              &MathTest::denormalize,
              &MathTest::pow,
              &MathTest::log);
 }
 
+void MathTest::constants() {
+    CORRADE_COMPARE(Math::pow<2>(Constants<float>::sqrt2()), 2.0f);
+    CORRADE_COMPARE(Math::pow<2>(Constants<float>::sqrt3()), 3.0f);
+
+    CORRADE_COMPARE(Math::pow<2>(Constants<double>::sqrt2()), 2.0);
+    CORRADE_COMPARE(Math::pow<2>(Constants<double>::sqrt3()), 3.0);
+}
+
 void MathTest::degrad() {
     CORRADE_COMPARE(deg(90.0), Constants<double>::pi()/2);
     CORRADE_COMPARE(deg(90.0f), Constants<float>::pi()/2);

src/Math/Test/MathTest.h

@@ -23,6 +23,7 @@ class MathTest: public Corrade::TestSuite::Tester<MathTest> {
     public:
         MathTest();
 
+        void constants();
         void degrad();
         void normalize();
         void denormalize();