MODULE random_function_mod
!------------------------------------------------------------------------------!
! Current revisions:
! -----------------
! 
!
! Former revisions:
! -----------------
! $Id: random_function.f90 484 2010-02-05 07:36:54Z witha $
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.3  2003/10/29 09:06:57  raasch
! Former function changed to a module.
!
! Revision 1.1  1998/02/04 16:09:45  raasch
! Initial revision
!
!
! Description:
! ------------
! Random number generator, produces numbers equally distributed in interval [0,1]
! This routine is taken from the "numerical recipies"
!------------------------------------------------------------------------------!

    IMPLICIT NONE

    PRIVATE

    PUBLIC random_function, random_function_ini

    INTEGER, PUBLIC, SAVE ::  random_iv(32), random_iy

    INTERFACE random_function_ini
       MODULE PROCEDURE random_function_ini
    END INTERFACE random_function_ini

    INTERFACE random_function
       MODULE PROCEDURE random_function
    END INTERFACE random_function

 CONTAINS

    SUBROUTINE random_function_ini

       IMPLICIT NONE

       random_iv = 0
       random_iy = 0

    END SUBROUTINE random_function_ini

    FUNCTION random_function( idum )


       IMPLICIT NONE

       INTEGER ::  ia, idum, im, iq, ir, ndiv, ntab
       REAL    ::  am, eps, random_function, ranf, rnmx

       PARAMETER ( ia=16807, im=2147483647, am=1.0/im, iq=127773, ir=2836, &
                   ntab=32, ndiv=1+(im-1)/ntab, eps=1.2e-7, rnmx=1.0-eps )

       INTEGER ::  j, k


       IF ( idum .le. 0  .or.  random_iy .eq. 0 )  THEN
          idum = max (-idum,1)
          DO  j = ntab+8,1,-1
             k    = idum / iq
             idum = ia * ( idum - k * iq ) - ir * k
             IF ( idum .lt. 0 )  idum = idum + im
             IF ( j .le. ntab )  random_iv(j) = idum
          ENDDO
          random_iy = random_iv(1)
       ENDIF

       k    = idum / iq
       idum = ia * ( idum - k * iq ) - ir * k
       IF ( idum .lt. 0 )  idum = idum + im
       j            = 1 + random_iy / ndiv
       random_iy    = random_iv(j)
       random_iv(j) = idum
       random_function  = min ( am * random_iy , rnmx )

    END FUNCTION random_function

 END MODULE random_function_mod