irev.F

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C> @file
C> @author WOOLLEN @date 1994-01-06
      
C> THIS FUNCTION WILL, WHEN THE LOCAL MACHINE IS "LITTLE-
C>   ENDIAN" (I.E., USES A RIGHT TO LEFT SCHEME FOR NUMBERING THE BYTES
C>   WITHIN A MACHINE WORD), RETURN A COPY OF AN INPUT INTEGER WORD WITH
C>   THE BYTES REVERSED.  ALTHOUGH, BY DEFINITION (WITHIN WMO MANUAL
C>   306), A BUFR MESSAGE IS A STREAM OF INDIVIDUAL OCTETS (I.E., BYTES)
C>   THAT IS INDEPENDENT OF ANY PARTICULAR MACHINE REPRESENTATION, THE
C>   BUFR ARCHIVE LIBRARY SOFTWARE OFTEN NEEDS TO INTERPRET ALL OR PARTS
C>   OF TWO OR MORE ADJACENT BYTES IN ORDER TO CONSTRUCT AN INTEGER
C>   WORD.  BY DEFAULT, THE SOFTWARE USES THE "BIG-ENDIAN" (LEFT TO
C>   RIGHT) SCHEME FOR NUMBERING BYTES.  BY REVERSING THE BYTES, IREV
C>   ALLOWS THE INTEGER WORD TO BE PROPERLY READ OR WRITTEN (DEPENDING
C>   ON WHETHER INPUT OR OUTPUT OPERATIONS, RESPECTIVELY, ARE BEING
C>   PERFORMED) ON LITTLE-ENDIAN MACHINES.  IF THE LOCAL MACHINE IS
C>   BIG-ENDIAN, IREV SIMPLY RETURNS A COPY OF THE SAME INTEGER THAT WAS
C>   INPUT.
C>
C> PROGRAM HISTORY LOG:
C> 1994-01-06  J. WOOLLEN -- ORIGINAL AUTHOR
C> 2003-11-04  J. ATOR    -- ADDED DOCUMENTATION
C> 2003-11-04  S. BENDER  -- ADDED REMARKS/BUFRLIB ROUTINE
C>                           INTERDEPENDENCIES
C> 2003-11-04  D. KEYSER  -- UNIFIED/PORTABLE FOR WRF; ADDED HISTORY
C>                           DOCUMENTATION
C> 2007-01-19  J. ATOR    -- BIG-ENDIAN VS. LITTLE-ENDIAN IS NOW
C>                           DETERMINED AT COMPILE TIME AND CONFIGURED
C>                           WITHIN BUFRLIB VIA CONDITIONAL COMPILATION
C>                           DIRECTIVES
C>
C> USAGE:    IREV (N)
C>   INPUT ARGUMENT LIST:
C>     N        - INTEGER: INTEGER WORD WITH BYTES ORDERED ACCORDING TO
C>                THE "BIG-ENDIAN" NUMBERING SCHEME
C>
C>   OUTPUT ARGUMENT LIST:
C>     IREV     - INTEGER: INTEGER WORD WITH BYTES ORDERED ACCORDING TO
C>                THE NUMBERING SCHEME OF THE LOCAL MACHINE (EITHER
C>                "BIG-ENDIAN" OR "LITTLE-ENDIAN", IF "BIG-ENDIAN THEN
C>                THIS IS JUST A DIRECT COPY OF N)
C>
C> REMARKS:
C>    THIS ROUTINE CALLS:        None
C>    THIS ROUTINE IS CALLED BY: IPKM     IUPM     PKB      PKC
C>                               UPBB
C>                               Normally not called by any application
C>                               programs.
C>
      FUNCTION irev(N)



      COMMON /hrdwrd/ nbytw,nbitw,iord(8)

      CHARACTER*8 cint,dint
      equivalence(cint,int)
      equivalence(dint,jnt)

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

#ifdef BIG_ENDIAN
      irev = n
#else
      int = n
      DO i=1,nbytw
        dint(i:i) = cint(iord(i):iord(i))
      ENDDO
      irev = jnt
#endif

      RETURN
      END