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*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
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