Make basic CDI functions constexpr (#1109)

* Make basic CDI functions constexpr

+ Move functions that don't require any class member data outside CDI class
+ Mark basic integration functions as constexpr
+ Remove files that formerly held low-level planck integration functions

* Don't use .data() yet, requires C++17

* Make CDI functions available on device

+ Hard code std::pow of max double as there's no constexpr pow in msvc
+ Add device/config to Cmake for CDI

src/cdi/CDI.cc

@@ -112,7 +112,7 @@ double CDI::integratePlanckSpectrum(size_t const groupIndex, double const T) {
   const double upper_bound = frequencyGroupBoundaries[groupIndex];
   Check(upper_bound > lower_bound);
 
-  double integral = integratePlanckSpectrum(lower_bound, upper_bound, T);
+  double integral = rtt_cdi::integratePlanckSpectrum(lower_bound, upper_bound, T);
 
   Ensure(integral >= 0.0);
   Ensure(integral <= 1.0);
@@ -136,7 +136,7 @@ double CDI::integratePlanckSpectrum(const double T) {
   Check(upper_bound > lower_bound);
 
   // calculate the integral
-  double integral = integratePlanckSpectrum(lower_bound, upper_bound, T);
+  double integral = rtt_cdi::integratePlanckSpectrum(lower_bound, upper_bound, T);
 
   Ensure(integral >= 0.0 && integral <= 1.0);
 
@@ -165,7 +165,7 @@ double CDI::integrateRosselandSpectrum(size_t const groupIndex, double const T)
   const double highFreq = frequencyGroupBoundaries[groupIndex];
   Check(highFreq > lowFreq);
 
-  double rosseland = integrateRosselandSpectrum(lowFreq, highFreq, T);
+  double rosseland = rtt_cdi::integrateRosselandSpectrum(lowFreq, highFreq, T);
 
   return rosseland;
 }
@@ -196,7 +196,7 @@ void CDI::integrate_Rosseland_Planckian_Spectrum(const size_t groupIndex, const
   Check(highFreq > lowFreq);
 
   // Call the general frequency version
-  integrate_Rosseland_Planckian_Spectrum(lowFreq, highFreq, T, planck, rosseland);
+  rtt_cdi::integrate_Rosseland_Planckian_Spectrum(lowFreq, highFreq, T, planck, rosseland);
   return;
 }