GeantUnits.h

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#ifndef DataFormats_Math_GeantUnits_h
#define DataFormats_Math_GeantUnits_h

// This file provides units represented with user-defined literals to more easily attach units to numerical values.
// Units here are based upon Geant conventions: millimeter = 1, MeV = 1.
// The CMS convention is that centimeter = 1 and GeV = 1, so care must be taken with code that converts between
// the two conventions.

#include "DataFormats/Math/interface/angle_units.h"

namespace geant_units {

  using angle_units::piRadians;  // Needed by files the include this file
  constexpr double joule(6.24150e+12);
  constexpr double seconds(1.e+9);
  constexpr double nanoseconds(1.);

  namespace operators {

    // The following are needed by files that include this header
    // Since "using namespace" is prohibited in header files, each
    // name is individually imported with a "using" statement.
    using angle_units::operators::operator""_deg;
    using angle_units::operators::operator""_pi;
    using angle_units::operators::operator""_rad;
    using angle_units::operators::almostEqual;
    using angle_units::operators::convertDegToRad;
    using angle_units::operators::convertRadToDeg;

    // Length
    constexpr double operator"" _mm(long double length) { return length * 1.; }
    constexpr double operator"" _cm(long double length) { return length * 10.; }
    constexpr double operator"" _m(long double length) { return length * 1000.; }
    constexpr double operator"" _cm3(long double length) { return length * 1._cm * 1._cm * 1._cm; }
    constexpr double operator"" _m3(long double length) { return length * 1._m * 1._m * 1._m; }
    constexpr double operator"" _mm(unsigned long long int length) { return length * 1; }
    constexpr double operator"" _cm(unsigned long long int length) { return length * 10; }

    // Time
    constexpr double operator"" _s(long double x) { return x * seconds; }
    constexpr double operator"" _ns(long double x) { return x * nanoseconds; }

    // Energy
    constexpr double operator"" _MeV(long double energy) { return energy * 1.; }
    constexpr double operator"" _eV(long double energy) { return energy * 1.e-6_MeV; }
    constexpr double operator"" _TeV(long double energy) { return energy * 1.e6_MeV; }
    constexpr double operator"" _GeV(long double energy) { return energy * 1000._MeV; }

    // Mass
    constexpr double operator"" _kg(long double mass) {
      return mass * (1._eV / 1.602176487e-19) * 1._s * 1._s / (1._m * 1._m);
    }
    constexpr double operator"" _g(long double mass) { return mass * 1.e-3_kg; }
    constexpr double operator"" _mg(long double mass) { return mass * 1.e-3_g; }
    constexpr double operator"" _mole(long double mass) { return mass * 1.; }

    // Material properties
    constexpr double operator"" _mg_per_cm3(long double density) { return density * 1._mg / 1._cm3; }
    constexpr double operator"" _g_per_cm3(long double density) { return density * 1._g / 1._cm3; }
    constexpr double operator"" _g_per_mole(long double mass) { return mass * 1._g / 1._mole; }

    // Add these conversion functions to this namespace for convenience
    using angle_units::operators::convertCm2ToMm2;
    using angle_units::operators::convertCmToMm;
    using angle_units::operators::convertGeVToKeV;
    using angle_units::operators::convertGeVToMeV;
    using angle_units::operators::convertMeVToGeV;
    using angle_units::operators::convertMm3ToM3;
    using angle_units::operators::convertMmToCm;

    // Convert Geant units to desired units
    template <class NumType>
    inline constexpr NumType convertUnitsTo(double desiredUnits, NumType val) {
      return (val / desiredUnits);
    }
  }  // namespace operators
}  // namespace geant_units

#endif