      SUBROUTINE DCOSQF (N,X,WSAVE)
      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
      DIMENSION       X(*)       ,WSAVE(*)
      DATA SQRT2 /1.41421356237309504880D0/
      IF (N.lt.2) GO TO 102
      IF (N.eq.2) GO TO 101
      GO TO 103
  101 TSQX = SQRT2*X(2)
      X(2) = X(1)-TSQX
      X(1) = X(1)+TSQX
  102 RETURN
  103 CALL DCOSQF1 (N,X,WSAVE,WSAVE(N+1))
      RETURN
      END

      SUBROUTINE DCOSQF1 (N,X,W,XH)
      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
      DIMENSION       X(1)       ,W(1)       ,XH(1)
      NS2 = (N+1)/2
      NP2 = N+2
      DO 101 K=2,NS2
         KC = NP2-K
         XH(K) = X(K)+X(KC)
         XH(KC) = X(K)-X(KC)
  101 CONTINUE
      MODN = MOD(N,2)
      IF (MODN .EQ. 0) XH(NS2+1) = X(NS2+1)+X(NS2+1)
      DO 102 K=2,NS2
         KC = NP2-K
         X(K) = W(K-1)*XH(KC)+W(KC-1)*XH(K)
         X(KC) = W(K-1)*XH(K)-W(KC-1)*XH(KC)
  102 CONTINUE
      IF (MODN .EQ. 0) X(NS2+1) = W(NS2)*XH(NS2+1)
      CALL DFFTF (N,X,XH)
      DO 103 I=3,N,2
         XIM1 = X(I-1)-X(I)
         X(I) = X(I-1)+X(I)
         X(I-1) = XIM1
  103 CONTINUE
      RETURN
      END

