COMP: make mathematical constants constexpr

- these are compile-time constants and can be marked as such in C++11.

src/OpenFOAM/global/constants/mathematical/mathematicalConstants.H

@@ -47,13 +47,13 @@ namespace mathematical
 
     static const char* const group = "mathematical";
 
-    const scalar e(M_E);
-    const scalar pi(M_PI);
-    const scalar twoPi(2*pi);
-    const scalar piByTwo(0.5*pi);
+    constexpr scalar e(M_E);
+    constexpr scalar pi(M_PI);
+    constexpr scalar twoPi(2*M_PI);
+    constexpr scalar piByTwo(0.5*M_PI);
 
     //- Euler's constant
-    const scalar Eu(0.57721566490153286060651209);
+    constexpr scalar Eu(0.57721566490153286060651209);
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 

src/OpenFOAM/global/unitConversion/unitConversion.H

@@ -44,14 +44,12 @@ namespace Foam
 //- Conversion from degrees to radians
 inline constexpr scalar degToRad(const scalar deg) noexcept
 {
-    //return (deg*Foam::constant::mathematical::pi/180.0);
     return (deg*M_PI/180.0);
 }
 
 //- Conversion from radians to degrees
 inline constexpr scalar radToDeg(const scalar rad) noexcept
 {
-    //return (rad*180.0/Foam::constant::mathematical::pi);
     return (rad*180.0/M_PI);
 }
 
@@ -71,14 +69,12 @@ inline constexpr scalar paToAtm(const scalar pa) noexcept
 //- User literal for degrees to radians conversion (integers)
 inline constexpr scalar operator "" _deg(unsigned long long int deg) noexcept
 {
-    //return (deg*Foam::constant::mathematical::pi/180.0);
     return (deg*M_PI/180.0);
 }
 
 //- User literal for degrees to radians conversion (floats)
 inline constexpr scalar operator "" _deg(long double deg) noexcept
 {
-    //return (deg*Foam::constant::mathematical::pi/180.0);
     return (deg*M_PI/180.0);
 }