SUBROUTINE OPENBT(lundx,mtyp)

C$$$  SUBPROGRAM DOCUMENTATION BLOCK
C
C SUBPROGRAM:    OPENBT
C   PRGMMR: J. ATOR          ORG: NP12        DATE: 2012-12-07
C
C ABSTRACT: Given a BUFR message type, this subroutine opens the
C   appropriate DX dictionary table in the specified table directory
C   as Fortran logical unit "lundx".  This subroutine overrides the
C   default subroutine of the same name in the NCEP BUFRLIB.
C
C PROGRAM HISTORY LOG:
C 2012-12-07  J. ATOR -- ORIGINAL AUTHOR
C
C USAGE:    CALL OPENBT ( lundx, mtyp )
C   INPUT ARGUMENT LIST:
C     mtyp     - integer: message type of input BUFR file
C
C   OUTPUT ARGUMENT LIST:
C     lundx    - integer: unit number of BUFR mnemonic table
C                  0 = unable to open table
C
C ATTRIBUTES:
C   LANGUAGE: FORTRAN 90
C   MACHINE:  Portable to all platforms
C
C$$$

        USE Share_Table_Info

        CHARACTER*11    bftab

        CHARACTER*240   bftabfil

        LOGICAL         exists

C-----------------------------------------------------------------------
C-----------------------------------------------------------------------

        WRITE ( bftab, '("bufrtab.",i3.3)' ) mtyp
        bftabfil = ctbldir(1:ltbd) // '/' // bftab

        INQUIRE ( FILE = bftabfil, EXIST = exists )
        IF ( exists ) THEN
            lundx = ludx
            CLOSE ( lundx )
            OPEN ( UNIT = lundx, FILE = bftabfil )
        ELSE
            lundx = 0
        END IF

        RETURN
        END