relibc_openlibm/slatec/radf4.f

*DECK RADF4
      SUBROUTINE RADF4 (IDO, L1, CC, CH, WA1, WA2, WA3)
C***BEGIN PROLOGUE  RADF4
C***SUBSIDIARY
C***PURPOSE  Calculate the fast Fourier transform of subvectors of
C            length four.
C***LIBRARY   SLATEC (FFTPACK)
C***TYPE      SINGLE PRECISION (RADF4-S)
C***AUTHOR  Swarztrauber, P. N., (NCAR)
C***ROUTINES CALLED  (NONE)
C***REVISION HISTORY  (YYMMDD)
C   790601  DATE WRITTEN
C   830401  Modified to use SLATEC library source file format.
C   860115  Modified by Ron Boisvert to adhere to Fortran 77 by
C           (a) changing dummy array size declarations (1) to (*).
C           (b) changing definition of variable HSQT2 by using
C               FORTRAN intrinsic function SQRT instead of a DATA
C               statement.
C   881128  Modified by Dick Valent to meet prologue standards.
C   890831  Modified array declarations.  (WRB)
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900402  Added TYPE section.  (WRB)
C***END PROLOGUE  RADF4
      DIMENSION CC(IDO,L1,4), CH(IDO,4,*), WA1(*), WA2(*), WA3(*)
C***FIRST EXECUTABLE STATEMENT  RADF4
      HSQT2 = .5*SQRT(2.)
      DO 101 K=1,L1
         TR1 = CC(1,K,2)+CC(1,K,4)
         TR2 = CC(1,K,1)+CC(1,K,3)
         CH(1,1,K) = TR1+TR2
         CH(IDO,4,K) = TR2-TR1
         CH(IDO,2,K) = CC(1,K,1)-CC(1,K,3)
         CH(1,3,K) = CC(1,K,4)-CC(1,K,2)
  101 CONTINUE
      IF (IDO-2) 107,105,102
  102 IDP2 = IDO+2
      IF((IDO-1)/2.LT.L1) GO TO 111
      DO 104 K=1,L1
CDIR$ IVDEP
         DO 103 I=3,IDO,2
            IC = IDP2-I
            CR2 = WA1(I-2)*CC(I-1,K,2)+WA1(I-1)*CC(I,K,2)
            CI2 = WA1(I-2)*CC(I,K,2)-WA1(I-1)*CC(I-1,K,2)
            CR3 = WA2(I-2)*CC(I-1,K,3)+WA2(I-1)*CC(I,K,3)
            CI3 = WA2(I-2)*CC(I,K,3)-WA2(I-1)*CC(I-1,K,3)
            CR4 = WA3(I-2)*CC(I-1,K,4)+WA3(I-1)*CC(I,K,4)
            CI4 = WA3(I-2)*CC(I,K,4)-WA3(I-1)*CC(I-1,K,4)
            TR1 = CR2+CR4
            TR4 = CR4-CR2
            TI1 = CI2+CI4
            TI4 = CI2-CI4
            TI2 = CC(I,K,1)+CI3
            TI3 = CC(I,K,1)-CI3
            TR2 = CC(I-1,K,1)+CR3
            TR3 = CC(I-1,K,1)-CR3
            CH(I-1,1,K) = TR1+TR2
            CH(IC-1,4,K) = TR2-TR1
            CH(I,1,K) = TI1+TI2
            CH(IC,4,K) = TI1-TI2
            CH(I-1,3,K) = TI4+TR3
            CH(IC-1,2,K) = TR3-TI4
            CH(I,3,K) = TR4+TI3
            CH(IC,2,K) = TR4-TI3
  103    CONTINUE
  104 CONTINUE
      GO TO 110
  111 DO 109 I=3,IDO,2
         IC = IDP2-I
CDIR$ IVDEP
         DO 108 K=1,L1
            CR2 = WA1(I-2)*CC(I-1,K,2)+WA1(I-1)*CC(I,K,2)
            CI2 = WA1(I-2)*CC(I,K,2)-WA1(I-1)*CC(I-1,K,2)
            CR3 = WA2(I-2)*CC(I-1,K,3)+WA2(I-1)*CC(I,K,3)
            CI3 = WA2(I-2)*CC(I,K,3)-WA2(I-1)*CC(I-1,K,3)
            CR4 = WA3(I-2)*CC(I-1,K,4)+WA3(I-1)*CC(I,K,4)
            CI4 = WA3(I-2)*CC(I,K,4)-WA3(I-1)*CC(I-1,K,4)
            TR1 = CR2+CR4
            TR4 = CR4-CR2
            TI1 = CI2+CI4
            TI4 = CI2-CI4
            TI2 = CC(I,K,1)+CI3
            TI3 = CC(I,K,1)-CI3
            TR2 = CC(I-1,K,1)+CR3
            TR3 = CC(I-1,K,1)-CR3
            CH(I-1,1,K) = TR1+TR2
            CH(IC-1,4,K) = TR2-TR1
            CH(I,1,K) = TI1+TI2
            CH(IC,4,K) = TI1-TI2
            CH(I-1,3,K) = TI4+TR3
            CH(IC-1,2,K) = TR3-TI4
            CH(I,3,K) = TR4+TI3
            CH(IC,2,K) = TR4-TI3
  108    CONTINUE
  109 CONTINUE
  110 IF (MOD(IDO,2) .EQ. 1) RETURN
  105 DO 106 K=1,L1
         TI1 = -HSQT2*(CC(IDO,K,2)+CC(IDO,K,4))
         TR1 = HSQT2*(CC(IDO,K,2)-CC(IDO,K,4))
         CH(IDO,1,K) = TR1+CC(IDO,K,1)
         CH(IDO,3,K) = CC(IDO,K,1)-TR1
         CH(1,2,K) = TI1-CC(IDO,K,3)
         CH(1,4,K) = TI1+CC(IDO,K,3)
  106 CONTINUE
  107 RETURN
      END