SUBROUTINE CF.XOR(a1, a2, result)
*
* Calculate decimal representation of XOR for those platforms that do not 
* include it in their standard arithmetic library.
*
* a1, a2: decimal integer operands
*
* result:  decimal XOR
*
* Be advised - there is no checking for illegal non-integer operands.
*
*    ========================================================================
*
*    Conditions of use:
*    This source code remains the property and copyright of Gulraj Rijhwani 
*    and Courtfields Limited.  Specific licence is granted to copy and use 
*    this program source, in accordance with the terms and conditions laid 
*    out following.  For the purposes of these terms and conditions the term
*    "developer" is defined to be the individual or company employing the
*    author incorporating use of this source.  Any use of this source code is
*    deemed to be full and unreserved acceptance of these stated terms.
*
*    1)  All instances of this source code must carry all attached
*        annotations and comments including, but not limited to, these
*        these conditions of use in their entirety.
*    2)  The developer may not alter the program source in any way, without
*        first obtaining the express written consent of duly authorised
*        company officers of Courtfields Limited, or its successors.
*    3)  This source code may not be included in whole or in part in any
*        proprietary program suite except as a separately compiled module
*        in wholly unmodified form.  Any installed object code must be
*        accompanied by the original source code at all times.
*    4)  In the event of any breach of these terms and conditions the
*        developer shall be liable for an annual usage charge of 200 pounds
*        sterling for every end user terminal or session using or having
*        access to use the resulting executable code.
*    5)  Gulraj Rijhwani and Courtfields Limited make no warranties for
*        the fitness of this source code, and may not be held liable
*        for any failure to fulfil the expectations or requirements of
*        the developer.
*
*    ========================================================================
*
     b = 1
     no.of.digits = LEN(a1)
     IF no.of.digits<LEN(a2) THEN no.of.digits = LEN(a2)
     result = 0
     FOR m=1 TO no.of.digits
      b2 = b * 2
      result = result + REM(a1-REM(a1,b)+a2-REM(a2,b),b2)
      b = b2
     NEXT m
*
     RETURN