Data Types and Sizes

Cactus knows about the following fixed size data types:

Data Type	Size (bytes)	Variable Type	Fortran Equivalent
CCTK_BYTE	1	CCTK_VARIABLE_BYTE	integer*1
CCTK_INT1	1	CCTK_VARIABLE_INT1	integer*1
CCTK_INT2	2	CCTK_VARIABLE_INT2	integer*2
CCTK_INT4	4	CCTK_VARIABLE_INT4	integer*4
CCTK_INT8	8	CCTK_VARIABLE_INT8	integer*8
CCTK_REAL4	4	CCTK_VARIABLE_REAL4	real*4
CCTK_REAL8	8	CCTK_VARIABLE_REAL8	real*8
CCTK_REAL16	16	CCTK_VARIABLE_REAL16	real*16
CCTK_COMPLEX8	8	CCTK_VARIABLE_COMPLEX8	complex*8
CCTK_COMPLEX16	16	CCTK_VARIABLE_COMPLEX16	complex*16
CCTK_COMPLEX32	32	CCTK_VARIABLE_COMPLEX32	complex*32

The availability of these types, and the corresponding C data types, are platform-dependent. For each fixed-size data type, there exists a corresponding preprocessor macro HAVE_<data type>, which should be used to check whether the given CCTK data type is supported, e.g.

  /* declare variable with extended-precision complex data type if available,
     otherwise, with default CCTK precision */
  #ifdef HAVE_CCTK_COMPLEX32
  CCTK_COMPLEX32 var;
  #else
  CCTK_COMPLEX   var;
  #endif

In addition, Cactus provides three generic numeric data types which map onto the compilers' native data types used to represent integer, real, and complex values. The size for these generic types can be chosen at configuration time (see Section A2.1.2). This is to allow the code to be run easily at different precisions. Note that the effectiveness of running the code, at a lower or higher precision, depends crucially on all thorns being used making consistent use of the these generic data types:

Data Type	Variable Type	Configuration Option
CCTK_INT	CCTK_VARIABLE_INT	INTEGER_PRECISION
CCTK_REAL	CCTK_VARIABLE_REAL	REAL_PRECISION
CCTK_COMPLEX	CCTK_VARIABLE_COMPLEX	Same as real precision

These variable types must be used by thorn writers to declare variables in the thorn interface files, and may be used to declare variables in the thorn routines. Note that variable declarations in thorns should obviously match the definitions in the interface files where appropriate.

A set of macros, which are interpreted by the preprocessor at compile time, to signify which data size is being used, are also provided:

Data Type	#define
CCTK_INT1	CCTK_INT_PRECISION_1
CCTK_INT2	CCTK_INT_PRECISION_2
CCTK_INT4	CCTK_INT_PRECISION_4
CCTK_INT8	CCTK_INT_PRECISION_8
CCTK_REAL4	CCTK_REAL_PRECISION_4
CCTK_REAL8	CCTK_REAL_PRECISION_8
CCTK_REAL16	CCTK_REAL_PRECISION_16
CCTK_COMPLEX8	CCTK_COMPLEX_PRECISION_8
CCTK_COMPLEX16	CCTK_COMPLEX_PRECISION_16
CCTK_COMPLEX32	CCTK_COMPLEX_PRECISION_32

Cactus also provides generic data and function pointers, which can be used from either C or Fortran:

Data Type	Variable Type	C equivalent
CCTK_POINTER	CCTK_VARIABLE_POINTER	void *data_ptr
CCTK_POINTER_TO_CONST	CCTK_VARIABLE_POINTER_TO_CONST	const void *data_ptr
CCTK_FPOINTER	CCTK_VARIABLE_FPOINTER	void (*fn_ptr)(void)