ADAS Subroutine d4open

       SUBROUTINE D4OPEN( IUNIT, DSFULL , LEXIST )
C-----------------------------------------------------------------------
C
C  ****************** FORTRAN77 SUBROUTINE: D4OPEN *********************
C
C  PURPOSE: TO INQUIRE & OPEN INPUT DATA FILE & ALLOCATE TO UNIT 'IUNIT'
C           (READ ONLY)  - IF IT DOES NOT EXISTS A MESSAGE IS  SENT  TO
C           THE SCREEN AND LEXIST IS RETURNED AS FALSE.
C
C           *** THIS VERSION SUPPRESSES ERROR MESSAGE ON NON-EXISTING
C               FILES. IT IS OTHERWISE IDENTICAL TO XXOPEN.
C
C  CALLING PROGRAM:  ADAS404
C
C  SUBROUTINE:
C
C  INPUT :    (I*4)  IUNIT   = UNIT TO WHICH INPUT FILE IS ALLOCATED
C  INPUT :    (C*(*))DSFULL  = FULL INPUT DATA SET NAME (INCL. USERID)
C                              IN FORM FOR DYNAMIC ALLOCATION.
C  OUTPUT:    (L*4)  LEXIST  = .TRUE.  => DATA SETS EXISTS AND IS OPEN
C                            = .FALSE. => DATA SET DOES NOT EXIST
C
C             (I*4)  I4UNIT  = FUNCTION (SEE ROUTINE SECTION BELOW)
C             (C*1)  BSLASH  = '/' - MUST BE FIRST 'DSFULL'CHARACTER
C NOTE:
C
C ROUTINES:
C          ROUTINE    SOURCE    BRIEF DESCRIPTION
C          ------------------------------------------------------------
C          I4UNIT     ADAS      FETCH UNIT NUMBER FOR OUTPUT OF MESSAGES
C          XXTERM     ADAS      TERMINATES ADAS PROGRAM WITH MESSAGE
C
C AUTHOR:  LORNE HORTON (JET)
C	     - BASED ON XXOPEN.
C
C DATE:    20-10-97
C-----------------------------------------------------------------------
C VERSION: 1.1						DATE:27-02-98
C MODIFIED: RICHARD MARTIN
C		- PUT UNDER SCCS CONTROL.
C
C VERSION: 1.2						DATE:17-05-07
C MODIFIED: Allan Whiteford
C		- Updated comments as part of subroutine documentation
C                 procedure.
C-----------------------------------------------------------------------
      CHARACTER*(*)       DSFULL
      INTEGER             IUNIT
      LOGICAL             LEXIST