LOGICAL FUNCTION LFLIP(PLOG)
C  This function returns the value .TRUE. with probability whose log is PLOG
C  if PLOG < 0.  Otherwise it returns the value .TRUE.
      IMPLICIT REAL*8 (A-H,O-Z)
      DATA ALO/-700.0D0/
      LFLIP=.TRUE.
      IF(PLOG.GE.0.0D0)RETURN
      IF(PLOG.LT.ALO)GO TO 10
      P=DEXP(PLOG)
      IF(DRNUNF().LE.P)RETURN
   10 LFLIP=.FALSE.
      RETURN
      END