rfftb1.f

      SUBROUTINE RFFTB1 (N,C,CH,WA,IFAC)
      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
      DIMENSION       CH(*)      ,C(*)       ,WA(*)      ,IFAC(*)
      NF = IFAC(2)
      NA = 0
      L1 = 1
      IW = 1
      DO 116 K1=1,NF
         IP = IFAC(K1+2)
         L2 = IP*L1
         IDO = N/L2
         IDL1 = IDO*L1
         IF (IP .NE. 4) GO TO 103
         IX2 = IW+IDO
         IX3 = IX2+IDO
         IF (NA .NE. 0) GO TO 101
         CALL RADB4 (IDO,L1,C,CH,WA(IW),WA(IX2),WA(IX3))
         GO TO 102
  101    CALL RADB4 (IDO,L1,CH,C,WA(IW),WA(IX2),WA(IX3))
  102    NA = 1-NA
         GO TO 115
  103    IF (IP .NE. 2) GO TO 106
         IF (NA .NE. 0) GO TO 104
         CALL RADB2 (IDO,L1,C,CH,WA(IW))
         GO TO 105
  104    CALL RADB2 (IDO,L1,CH,C,WA(IW))
  105    NA = 1-NA
         GO TO 115
  106    IF (IP .NE. 3) GO TO 109
         IX2 = IW+IDO
         IF (NA .NE. 0) GO TO 107
         CALL RADB3 (IDO,L1,C,CH,WA(IW),WA(IX2))
         GO TO 108
  107    CALL RADB3 (IDO,L1,CH,C,WA(IW),WA(IX2))
  108    NA = 1-NA
         GO TO 115
  109    IF (IP .NE. 5) GO TO 112
         IX2 = IW+IDO
         IX3 = IX2+IDO
         IX4 = IX3+IDO
         IF (NA .NE. 0) GO TO 110
         CALL RADB5 (IDO,L1,C,CH,WA(IW),WA(IX2),WA(IX3),WA(IX4))
         GO TO 111
  110    CALL RADB5 (IDO,L1,CH,C,WA(IW),WA(IX2),WA(IX3),WA(IX4))
  111    NA = 1-NA
         GO TO 115
  112    IF (NA .NE. 0) GO TO 113
         CALL RADBG (IDO,IP,L1,IDL1,C,C,C,CH,CH,WA(IW))
         GO TO 114
  113    CALL RADBG (IDO,IP,L1,IDL1,CH,CH,CH,C,C,WA(IW))
  114    IF (IDO .EQ. 1) NA = 1-NA
  115    L1 = L2
         IW = IW+(IP-1)*IDO
  116 CONTINUE
      IF (NA .EQ. 0) RETURN
      DO 117 I=1,N
         C(I) = CH(I)
  117 CONTINUE
      RETURN
      END