Units.h

// -*- C++ -*-
//
// This file is part of HepMC
// Copyright (C) 2014-2023 The HepMC collaboration (see AUTHORS for details)
//
#ifndef HEPMC3_UNITS_H
#define HEPMC3_UNITS_H
#include <string>
#include "HepMC3/Errors.h"
#include "HepMC3/Setup.h"
#include "HepMC3/FourVector.h"
 
namespace HepMC3 {
 
 
class Units {
public:
    enum MomentumUnit { MEV, GEV };

    enum LengthUnit   { MM,  CM  };
 
public:
    static MomentumUnit momentum_unit( const std::string& name ) {
        if ( name.compare(0,3,"GEV") == 0 ) return GEV;
        if ( name.compare(0,3,"MEV") == 0 ) return MEV;
 
        HEPMC3_ERROR_LEVEL(300,"Units::momentum_unit: unrecognised unit name: '" << name <<"', setting to GEV" )
 
        return GEV;
    }

    static LengthUnit length_unit( const std::string& name ) {
        if ( name.compare(0,2,"CM") == 0 ) return CM;
        if ( name.compare(0,2,"MM") == 0 ) return MM;
 
        HEPMC3_ERROR_LEVEL(300,"Units::length_unit: unrecognised unit name: '" << name <<"', setting to CM" )
 
        return CM;
    }

    static std::string name( MomentumUnit u ) {
        switch(u) {
        case MEV:
            return "MEV";
        case GEV:
            return "GEV";
        }
 
        return "<UNDEFINED>";
    }

    static std::string name( LengthUnit u ) {
        switch(u) {
        case MM:
            return "MM";
        case CM:
            return "CM";
        }
 
        return "<UNDEFINED>";
    }

    template <typename T>
    static void convert( T &m, MomentumUnit from, MomentumUnit to ) {
        if ( from == to ) return;
 
        if ( from == GEV ) {
            // GEV -> MEV
            m *= 1000.;
        }
        else if ( from == MEV ) {
            // MEV -> GEV
            m *= 0.001;
        }
    }

    template <typename T>
    static void convert( T &m, LengthUnit from, LengthUnit to ) {
        if ( from == to ) return;
 
        if ( from == CM ) {
            // CM -> MM
            m *= 10.0;
        }
        else if ( from == MM ) {
            // MM -> CM
            m *= 0.1;
        }
    }
 
};
 
} // namespace HepMC3
 
#endif