*-- Author : S.Burke / J.V. Morris
      DOUBLE PRECISION FUNCTION FKDPHI(PHI1,PHI2)
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*                                                                    *                                        
* Compute FKDPHI = PHI1-PHI2 , where PHI1 and PHI2 are in the range  *                                        
* zero to twopi.                                                     *                                        
* FKDPHI is between -pi and +pi                                      *                                        
*                                                                    *                                        
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*KEEP,FKPIDP.                                                                                                 
*KEND.                                                                                                        
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*                                                                                                             
*-----------------------------------------Updates 21/09/92-------                                             
**: FKETOI.......SB. Cope better (?) with zero field.                                                         
*-----------------------------------------Updates----------------