relibc_openlibm/slatec/radb4.f

*DECK RADB4
      SUBROUTINE RADB4 (IDO, L1, CC, CH, WA1, WA2, WA3)
C***BEGIN PROLOGUE  RADB4
C***SUBSIDIARY
C***PURPOSE  Calculate the fast Fourier transform of subvectors of
C            length four.
C***LIBRARY   SLATEC (FFTPACK)
C***TYPE      SINGLE PRECISION (RADB4-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 SQRT2 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  RADB4
      DIMENSION CC(IDO,4,*), CH(IDO,L1,4), WA1(*), WA2(*), WA3(*)
C***FIRST EXECUTABLE STATEMENT  RADB4
      SQRT2 = SQRT(2.)
      DO 101 K=1,L1
         TR1 = CC(1,1,K)-CC(IDO,4,K)
         TR2 = CC(1,1,K)+CC(IDO,4,K)
         TR3 = CC(IDO,2,K)+CC(IDO,2,K)
         TR4 = CC(1,3,K)+CC(1,3,K)
         CH(1,K,1) = TR2+TR3
         CH(1,K,2) = TR1-TR4
         CH(1,K,3) = TR2-TR3
         CH(1,K,4) = TR1+TR4
  101 CONTINUE
      IF (IDO-2) 107,105,102
  102 IDP2 = IDO+2
      IF((IDO-1)/2.LT.L1) GO TO 108
      DO 104 K=1,L1
CDIR$ IVDEP
         DO 103 I=3,IDO,2
            IC = IDP2-I
            TI1 = CC(I,1,K)+CC(IC,4,K)
            TI2 = CC(I,1,K)-CC(IC,4,K)
            TI3 = CC(I,3,K)-CC(IC,2,K)
            TR4 = CC(I,3,K)+CC(IC,2,K)
            TR1 = CC(I-1,1,K)-CC(IC-1,4,K)
            TR2 = CC(I-1,1,K)+CC(IC-1,4,K)
            TI4 = CC(I-1,3,K)-CC(IC-1,2,K)
            TR3 = CC(I-1,3,K)+CC(IC-1,2,K)
            CH(I-1,K,1) = TR2+TR3
            CR3 = TR2-TR3
            CH(I,K,1) = TI2+TI3
            CI3 = TI2-TI3
            CR2 = TR1-TR4
            CR4 = TR1+TR4
            CI2 = TI1+TI4
            CI4 = TI1-TI4
            CH(I-1,K,2) = WA1(I-2)*CR2-WA1(I-1)*CI2
            CH(I,K,2) = WA1(I-2)*CI2+WA1(I-1)*CR2
            CH(I-1,K,3) = WA2(I-2)*CR3-WA2(I-1)*CI3
            CH(I,K,3) = WA2(I-2)*CI3+WA2(I-1)*CR3
            CH(I-1,K,4) = WA3(I-2)*CR4-WA3(I-1)*CI4
            CH(I,K,4) = WA3(I-2)*CI4+WA3(I-1)*CR4
  103    CONTINUE
  104 CONTINUE
      GO TO 111
  108 DO 110 I=3,IDO,2
         IC = IDP2-I
CDIR$ IVDEP
         DO 109 K=1,L1
            TI1 = CC(I,1,K)+CC(IC,4,K)
            TI2 = CC(I,1,K)-CC(IC,4,K)
            TI3 = CC(I,3,K)-CC(IC,2,K)
            TR4 = CC(I,3,K)+CC(IC,2,K)
            TR1 = CC(I-1,1,K)-CC(IC-1,4,K)
            TR2 = CC(I-1,1,K)+CC(IC-1,4,K)
            TI4 = CC(I-1,3,K)-CC(IC-1,2,K)
            TR3 = CC(I-1,3,K)+CC(IC-1,2,K)
            CH(I-1,K,1) = TR2+TR3
            CR3 = TR2-TR3
            CH(I,K,1) = TI2+TI3
            CI3 = TI2-TI3
            CR2 = TR1-TR4
            CR4 = TR1+TR4
            CI2 = TI1+TI4
            CI4 = TI1-TI4
            CH(I-1,K,2) = WA1(I-2)*CR2-WA1(I-1)*CI2
            CH(I,K,2) = WA1(I-2)*CI2+WA1(I-1)*CR2
            CH(I-1,K,3) = WA2(I-2)*CR3-WA2(I-1)*CI3
            CH(I,K,3) = WA2(I-2)*CI3+WA2(I-1)*CR3
            CH(I-1,K,4) = WA3(I-2)*CR4-WA3(I-1)*CI4
            CH(I,K,4) = WA3(I-2)*CI4+WA3(I-1)*CR4
  109    CONTINUE
  110 CONTINUE
  111 IF (MOD(IDO,2) .EQ. 1) RETURN
  105 DO 106 K=1,L1
         TI1 = CC(1,2,K)+CC(1,4,K)
         TI2 = CC(1,4,K)-CC(1,2,K)
         TR1 = CC(IDO,1,K)-CC(IDO,3,K)
         TR2 = CC(IDO,1,K)+CC(IDO,3,K)
         CH(IDO,K,1) = TR2+TR2
         CH(IDO,K,2) = SQRT2*(TR1-TI1)
         CH(IDO,K,3) = TI2+TI2
         CH(IDO,K,4) = -SQRT2*(TR1+TI1)
  106 CONTINUE
  107 RETURN
      END