FUNCTION random_gauss( idum, upper_limit )

!--------------------------------------------------------------------------------!
! This file is part of PALM.
!
! PALM is free software: you can redistribute it and/or modify it under the terms
! of the GNU General Public License as published by the Free Software Foundation,
! either version 3 of the License, or (at your option) any later version.
!
! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License along with
! PALM. If not, see <http://www.gnu.org/licenses/>.
!
! Copyright 1997-2012  Leibniz University Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
! 
!
! Former revisions:
! -----------------
! $Id: random_gauss.f90 1037 2012-10-22 14:10:22Z franke $
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.4  2006/08/04 15:01:48  raasch
! Range of random number is limited by an upper limit (new second parameter)
!
! Revision 1.1  1998/03/25 20:09:47  raasch
! Initial revision
!
!
! Description:
! ------------
! Generates a gaussian distributed random number (mean value 1, sigma = 1)
! This routine is taken from the "numerical recipies".
!------------------------------------------------------------------------------!

    USE random_function_mod

    IMPLICIT NONE

    INTEGER :: idum, iset
    REAL    :: fac, gset, random_gauss, rsq, upper_limit, v1, v2

    SAVE  iset, gset

    DATA  iset /0/

!
!-- Random numbers are created as long as they do not fall below the given
!-- upper limit
    DO

       IF ( iset == 0 )  THEN
          rsq = 0.0
          DO  WHILE ( rsq >= 1.0  .OR.  rsq == 0.0 )
             v1  = 2.0 * random_function( idum ) - 1.0
             v2  = 2.0 * random_function( idum ) - 1.0
             rsq = v1**2 + v2**2
          ENDDO
          fac          = SQRT( -2.0 * LOG( rsq ) / rsq )
          gset         = v1 * fac
          random_gauss = v2 * fac + 1.0
          iset         = 1
       ELSE
          random_gauss = gset + 1.0
          iset         = 0
       ENDIF

       IF ( ABS( random_gauss - 1.0 ) <= upper_limit )  EXIT

    ENDDO

 END FUNCTION random_gauss