C                                                                       00010001
C***********************************************************************
C                 COPYRIGHT ATLANTIC RICHFIELD COMPANY 1991            *
C***********************************************************************
CTITLESAHILBT -- PERFORM HILBERT TRANSFORM                              00020001
CA
CA    AUTHOR       B. S. BOK                                            00030001
CA    DESIGNER     B. S. BOK                                            00040001
CA    LANGUAGE     FORTRAN                                              00050001
CA    SYSTEM       IBM                                                  00060001
CA    WRITTEN      AUGUST, 1990                                         00070001
C     REVISED      12-21-91 JJC - MODIFIED TO MEET EDP STANDARDS.
CA                                                                      00090001
CA    CALL SAHILBT(X, Y, NN, NU)
CA                                                                      00110001
CA         INPUT   X     = INPUT TRACE                               R4 00120001
CA         INPUT   NU    = MAGNITUDE OF FFT (NN = 2**NU)             I4 00130001
CA         INPUT   NN    = FFT LENGTH                                I4
CA         OUTPUT  Y     = HILBERT TRANSFORM OF X                    R4 00140001
CA
CA    THIS SUBROUTINE PERFORMS THE HILBERT TRANSFORM
C
C**************************************************************
C                                                             *
C SUBROUTINES AND FUNCTIONS CALLED FROM THIS ROUTINE          *
C                                                             *
C MFORSP                                                      *
C                                                             *
C**************************************************************
C
      SUBROUTINE SAHILBT(X,Y,NN,NU)
C
      IMPLICIT INTEGER (A-Z)
C
      DIMENSION X(NN),Y(NN)
      REAL    X
      REAL    Y
C
      NH = NN / 2
      NYQ1 = NH + 2
C
      DO 100 N = 1, NN
         Y(N) = 0.
 100  CONTINUE
CJJ   CALL BBFFT ( X, Y, NN, NU, 0 )
      CALL MFORSP(NU, X, Y, -1 )
      DO 120 N = 2, NH
         X(N) = 2. * X(N)
         Y(N) = 2. * Y(N)
 120  CONTINUE
      NH = NH + 2
      DO 140 N = NYQ1, NN
         X(N) = 0.
         Y(N) = 0.
 140  CONTINUE
CJJ   CALL BBFFT ( X, Y, NN, NU, 1 )
      CALL MFORSP( NU, X, Y, 1 )
C
      RETURN
      END