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*DECK RADF3
SUBROUTINE RADF3 (IDO, L1, CC, CH, WA1, WA2)
C***BEGIN PROLOGUE RADF3
C***SUBSIDIARY
C***PURPOSE Calculate the fast Fourier transform of subvectors of
C length three.
C***LIBRARY SLATEC (FFTPACK)
C***TYPE SINGLE PRECISION (RADF3-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 TAUI 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 RADF3
DIMENSION CH(IDO,3,*), CC(IDO,L1,3), WA1(*), WA2(*)
C***FIRST EXECUTABLE STATEMENT RADF3
TAUR = -.5
TAUI = .5*SQRT(3.)
DO 101 K=1,L1
CR2 = CC(1,K,2)+CC(1,K,3)
CH(1,1,K) = CC(1,K,1)+CR2
CH(1,3,K) = TAUI*(CC(1,K,3)-CC(1,K,2))
CH(IDO,2,K) = CC(1,K,1)+TAUR*CR2
101 CONTINUE
IF (IDO .EQ. 1) RETURN
IDP2 = IDO+2
IF((IDO-1)/2.LT.L1) GO TO 104
DO 103 K=1,L1
CDIR$ IVDEP
DO 102 I=3,IDO,2
IC = IDP2-I
DR2 = WA1(I-2)*CC(I-1,K,2)+WA1(I-1)*CC(I,K,2)
DI2 = WA1(I-2)*CC(I,K,2)-WA1(I-1)*CC(I-1,K,2)
DR3 = WA2(I-2)*CC(I-1,K,3)+WA2(I-1)*CC(I,K,3)
DI3 = WA2(I-2)*CC(I,K,3)-WA2(I-1)*CC(I-1,K,3)
CR2 = DR2+DR3
CI2 = DI2+DI3
CH(I-1,1,K) = CC(I-1,K,1)+CR2
CH(I,1,K) = CC(I,K,1)+CI2
TR2 = CC(I-1,K,1)+TAUR*CR2
TI2 = CC(I,K,1)+TAUR*CI2
TR3 = TAUI*(DI2-DI3)
TI3 = TAUI*(DR3-DR2)
CH(I-1,3,K) = TR2+TR3
CH(IC-1,2,K) = TR2-TR3
CH(I,3,K) = TI2+TI3
CH(IC,2,K) = TI3-TI2
102 CONTINUE
103 CONTINUE
RETURN
104 DO 106 I=3,IDO,2
IC = IDP2-I
CDIR$ IVDEP
DO 105 K=1,L1
DR2 = WA1(I-2)*CC(I-1,K,2)+WA1(I-1)*CC(I,K,2)
DI2 = WA1(I-2)*CC(I,K,2)-WA1(I-1)*CC(I-1,K,2)
DR3 = WA2(I-2)*CC(I-1,K,3)+WA2(I-1)*CC(I,K,3)
DI3 = WA2(I-2)*CC(I,K,3)-WA2(I-1)*CC(I-1,K,3)
CR2 = DR2+DR3
CI2 = DI2+DI3
CH(I-1,1,K) = CC(I-1,K,1)+CR2
CH(I,1,K) = CC(I,K,1)+CI2
TR2 = CC(I-1,K,1)+TAUR*CR2
TI2 = CC(I,K,1)+TAUR*CI2
TR3 = TAUI*(DI2-DI3)
TI3 = TAUI*(DR3-DR2)
CH(I-1,3,K) = TR2+TR3
CH(IC-1,2,K) = TR2-TR3
CH(I,3,K) = TI2+TI3
CH(IC,2,K) = TI3-TI2
105 CONTINUE
106 CONTINUE
RETURN
END
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