DataTypeSizes.f90 Source File

!!  Provide named kind parameters for use in declarations of 
!!   real and integer variables with specific byte sizes
!|author:  <a href="mailto:giovanni.ravazzani@polimi.it">Giovanni Ravazzani</a>
! license: <a href="http://www.gnu.org/licenses/">GPL</a>
!    
!### History
!
! current version: 1.0 - 4th July 2008 
!
! | version  |  date       |  comment |
! |----------|-------------|----------|
! | 1.0      | 4/Jul/2008 | Original code |
!
!
!### License  
! license: GNU GPL <http://www.gnu.org/licenses/>
!
! This file is part of 
!
!   MOSAICO -- MOdular library for raSter bAsed hydrologIcal appliCatiOn.
! 
!   Copyright (C) 2011 Giovanni Ravazzani
!
!### Code Description 
!   Language: Fortran 90. 
!
!   Software Standards: "European Standards for Writing and  
!   Documenting Exchangeable Fortran 90 Code". 
! 
!### Module Description 
!  
! Motivation: 
!
!   Portability refers to the ease with which source code can be moved 
!   from machine to machine. A portable program requires little or no 
!   change to the source code when compiled and run on a different machine. 
!   Portability of numerical code is important for several reasons.
!   Fortran 90 introduces several new mechanisms to aid in porting numerical 
!   code to other machines. The most difficult problem in porting numerical 
!   programs is in the portable selection of precision. Selecting the precision 
!   of a computation in a portable way was impossible with Fortran 77. 
!   However, with the introduction of kind values as well as intrinsic 
!   environmental inquiry functions for selecting and inquiring about 
!   precision, Fortran 90 programs should be much easier to port to other machines.
!   Kind values are integer constants that can be used to further specify 
!   the characteristics of an intrinsic type, such as integer or real. 
!   For example, real( 2 ) selects a real type with kind value 2. 
!   Unfortunately, kind values are processor-dependent and are therefore 
!   not standardized. However, there are several portable ways to 
!   select kind values based on the precision desired. Two such functions 
!   are selected_int_kind and selected_real_kind
!
! Description: 
!
!   Provide named kind parameters for use in declarations of real and integer 
!   variables with specific byte sizes (i.e. one, two, four, and eight byte
!   integers; four and eight byte reals). The parameters can then be used
!   in (KIND = XX) modifiers in declarations.
!   A single function (SizesOK()) is provided to ensure that the selected 
!   kind parameters are correct.
!
! References and Credits:
!
!   Adapted from netCDF library http://www.unidata.ucar.edu/software/netcdf/
!   Written by Robert Pincus
!
! Design Notes:
!
!   Fortran 90 doesn't allow one to check the number of bytes in a real variable;
!   we check only that four byte and eight byte reals have different kind parameters. 
!
MODULE DataTypeSizes        

IMPLICIT NONE 

! Global (i.e. public) Declarations: 

!| 32 bits integer type
!equivalent to FourByteInt type in netCDF library
 INTEGER, PUBLIC, PARAMETER ::   short = SELECTED_INT_KIND(9)

!| 64 bits integer type
!equivalent to EightByteInt type in netCDF library
 INTEGER, PUBLIC, PARAMETER ::   long = SELECTED_INT_KIND(18)

!| 32 bits real type
! floating point numbers with numerical precision at least 6  digits 
! and one decimal exponent range between -37  and +37
! equivalent to FourByteReal type in netCDF library                       
INTEGER, PUBLIC, PARAMETER :: float = SELECTED_REAL_KIND(P =  6, R =  37) 


!| 64 bits real type
! floating point numbers with numerical precision at least 13  digits 
! and one decimal exponent range between -307  and +307
! equivalent to EightByteReal type in netCDF library (double precision)
INTEGER, PUBLIC, PARAMETER :: double = SELECTED_REAL_KIND(P = 13, R = 307) 



!=======
CONTAINS
!=======
! Define procedures contained in this module. 

!==============================================================================
!| Description:
! Users may call this function once to ensure that the kind parameters 
! the module defines are available with the current compiler. 
! We can't ensure that the two REAL kinds are actually four and 
! eight bytes long, but we can ensure that they are distinct. 
! Early Fortran 90 compilers would sometimes report incorrect results for 
! the bit_size intrinsic, but I haven't seen this in a long time. 
LOGICAL FUNCTION SizesOK &
!
()

IMPLICIT NONE

! Local scalars:
INTEGER (KIND = short)  :: short_int
INTEGER (KIND = long)   :: long_int
REAL    (KIND = float)  :: float_real
REAL    (KIND = double) :: double_real
!------------end of declaration------------------------------------------------

  IF (BIT_SIZE( short_int) == 32  .AND. BIT_SIZE( long_int) == 64 .AND.  &
      float > 0 .AND. double > 0  .AND. float /= double                  ) THEN
      SizesOK = .TRUE.
  ELSE
      SizesOK = .FALSE.
  END IF
END FUNCTION SizesOK

END MODULE DataTypeSizes