Units.h File Reference

Wrapper to avoid constant divisions when using units. More...

#include "GaudiKernel/SystemOfUnits.h"
#include "GaudiKernel/PhysicalConstants.h"

Include dependency graph for Units.h:

Go to the source code of this file.

Classes
class	Athena::Units::Unit< TAG >
	Wrapper to avoid constant divisions when using units. More...

Namespaces
namespace	Athena
	Some weak symbol referencing magic... These are declared in AthenaKernel/getMessageSvc.h and will be non-nullptr in case the GaudiSvc/AthenaKernel shared libraries have been loaded.
namespace	Athena::Units

Macros
#define	UNIT(NAME)

Functions
template<int TAG>
constexpr double	Athena::Units::operator/ (double x, const Unit< TAG > u)
template<int TAG>
constexpr float	Athena::Units::operator/ (float x, const Unit< TAG > u)
	Athena::Units::UNIT (millimeter)
	Athena::Units::UNIT (millimeter2)
	Athena::Units::UNIT (millimeter3)
	Athena::Units::UNIT (centimeter)
	Athena::Units::UNIT (centimeter2)
	Athena::Units::UNIT (centimeter3)
	Athena::Units::UNIT (meter)
	Athena::Units::UNIT (meter2)
	Athena::Units::UNIT (meter3)
	Athena::Units::UNIT (micrometer)
	Athena::Units::UNIT (um)
	Athena::Units::UNIT (mm)
	Athena::Units::UNIT (mm2)
	Athena::Units::UNIT (mm3)
	Athena::Units::UNIT (cm)
	Athena::Units::UNIT (cm2)
	Athena::Units::UNIT (cm3)
	Athena::Units::UNIT (radian)
	Athena::Units::UNIT (degree)
	Athena::Units::UNIT (rad)
	Athena::Units::UNIT (deg)
	Athena::Units::UNIT (picosecond)
	Athena::Units::UNIT (nanosecond)
	Athena::Units::UNIT (microsecond)
	Athena::Units::UNIT (millisecond)
	Athena::Units::UNIT (second)
	Athena::Units::UNIT (ns)
	Athena::Units::UNIT (s)
	Athena::Units::UNIT (ms)
	Athena::Units::UNIT (keV)
	Athena::Units::UNIT (MeV)
	Athena::Units::UNIT (GeV)
	Athena::Units::UNIT (TeV)
	Athena::Units::UNIT (gram)
	Athena::Units::UNIT (g)
	Athena::Units::UNIT (mole)
	Athena::Units::UNIT (c_light)

Detailed Description

Wrapper to avoid constant divisions when using units.

Author

scott snyder snyde.nosp@m.r@bn.nosp@m.l.gov

Date

Jun, 2015

A typical use of the unit symbols is like

double pt_in_gev = pt / GeV;

However, writing it like this results in a division by a constant being generated. It would be faster to rewrite this as multiplication by the inverse, but the compiler won't do that by default as the results are not guaranteed to be the same.

Using the symbols defined here allow avoiding the divisions (in optimized builds) without having to write the above explicitly as

double pt_in_gev = pt * (1./GeV);

which is pretty ugly.

We do this by creating a static const object wrapping the value of the unit and overriding operator/ to change the division to multiplication by inverse.

Definition in file Units.h.

Macro Definition Documentation

UNIT

#define UNIT

(

NAME

)

Value:

template <> class Unit<__LINE__>                                        \
{                                                                       \
public:                                                                 \
  constexpr operator double() const { return Gaudi::Units::NAME; }      \
};                                                                      \
constexpr static const Unit<__LINE__> NAME

Definition at line 74 of file Units.h.

#define UNIT(NAME)                                                      \
template <> class Unit<__LINE__>                                        \
{                                                                       \
public:                                                                 \
  constexpr operator double() const { return Gaudi::Units::NAME; }      \
};                                                                      \
constexpr static const Unit<__LINE__> NAME