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100 lines
3.4 KiB
Fortran
100 lines
3.4 KiB
Fortran
*DECK PASSB4
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SUBROUTINE PASSB4 (IDO, L1, CC, CH, WA1, WA2, WA3)
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C***BEGIN PROLOGUE PASSB4
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C***SUBSIDIARY
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C***PURPOSE Calculate the fast Fourier transform of subvectors of
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C length four.
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C***LIBRARY SLATEC (FFTPACK)
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C***TYPE SINGLE PRECISION (PASSB4-S)
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C***AUTHOR Swarztrauber, P. N., (NCAR)
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 790601 DATE WRITTEN
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C 830401 Modified to use SLATEC library source file format.
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C 860115 Modified by Ron Boisvert to adhere to Fortran 77 by
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C changing dummy array size declarations (1) to (*).
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C 881128 Modified by Dick Valent to meet prologue standards.
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C 890831 Modified array declarations. (WRB)
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 900402 Added TYPE section. (WRB)
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C***END PROLOGUE PASSB4
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DIMENSION CC(IDO,4,*), CH(IDO,L1,4), WA1(*), WA2(*), WA3(*)
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C***FIRST EXECUTABLE STATEMENT PASSB4
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IF (IDO .NE. 2) GO TO 102
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DO 101 K=1,L1
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TI1 = CC(2,1,K)-CC(2,3,K)
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TI2 = CC(2,1,K)+CC(2,3,K)
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TR4 = CC(2,4,K)-CC(2,2,K)
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TI3 = CC(2,2,K)+CC(2,4,K)
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TR1 = CC(1,1,K)-CC(1,3,K)
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TR2 = CC(1,1,K)+CC(1,3,K)
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TI4 = CC(1,2,K)-CC(1,4,K)
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TR3 = CC(1,2,K)+CC(1,4,K)
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CH(1,K,1) = TR2+TR3
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CH(1,K,3) = TR2-TR3
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CH(2,K,1) = TI2+TI3
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CH(2,K,3) = TI2-TI3
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CH(1,K,2) = TR1+TR4
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CH(1,K,4) = TR1-TR4
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CH(2,K,2) = TI1+TI4
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CH(2,K,4) = TI1-TI4
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101 CONTINUE
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RETURN
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102 IF(IDO/2.LT.L1) GO TO 105
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DO 104 K=1,L1
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CDIR$ IVDEP
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DO 103 I=2,IDO,2
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TI1 = CC(I,1,K)-CC(I,3,K)
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TI2 = CC(I,1,K)+CC(I,3,K)
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TI3 = CC(I,2,K)+CC(I,4,K)
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TR4 = CC(I,4,K)-CC(I,2,K)
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TR1 = CC(I-1,1,K)-CC(I-1,3,K)
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TR2 = CC(I-1,1,K)+CC(I-1,3,K)
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TI4 = CC(I-1,2,K)-CC(I-1,4,K)
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TR3 = CC(I-1,2,K)+CC(I-1,4,K)
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CH(I-1,K,1) = TR2+TR3
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CR3 = TR2-TR3
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CH(I,K,1) = TI2+TI3
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CI3 = TI2-TI3
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CR2 = TR1+TR4
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CR4 = TR1-TR4
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CI2 = TI1+TI4
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CI4 = TI1-TI4
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CH(I-1,K,2) = WA1(I-1)*CR2-WA1(I)*CI2
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CH(I,K,2) = WA1(I-1)*CI2+WA1(I)*CR2
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CH(I-1,K,3) = WA2(I-1)*CR3-WA2(I)*CI3
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CH(I,K,3) = WA2(I-1)*CI3+WA2(I)*CR3
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CH(I-1,K,4) = WA3(I-1)*CR4-WA3(I)*CI4
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CH(I,K,4) = WA3(I-1)*CI4+WA3(I)*CR4
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103 CONTINUE
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104 CONTINUE
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RETURN
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105 DO 107 I=2,IDO,2
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CDIR$ IVDEP
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DO 106 K=1,L1
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TI1 = CC(I,1,K)-CC(I,3,K)
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TI2 = CC(I,1,K)+CC(I,3,K)
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TI3 = CC(I,2,K)+CC(I,4,K)
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TR4 = CC(I,4,K)-CC(I,2,K)
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TR1 = CC(I-1,1,K)-CC(I-1,3,K)
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TR2 = CC(I-1,1,K)+CC(I-1,3,K)
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TI4 = CC(I-1,2,K)-CC(I-1,4,K)
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TR3 = CC(I-1,2,K)+CC(I-1,4,K)
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CH(I-1,K,1) = TR2+TR3
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CR3 = TR2-TR3
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CH(I,K,1) = TI2+TI3
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CI3 = TI2-TI3
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CR2 = TR1+TR4
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CR4 = TR1-TR4
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CI2 = TI1+TI4
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CI4 = TI1-TI4
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CH(I-1,K,2) = WA1(I-1)*CR2-WA1(I)*CI2
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CH(I,K,2) = WA1(I-1)*CI2+WA1(I)*CR2
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CH(I-1,K,3) = WA2(I-1)*CR3-WA2(I)*CI3
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CH(I,K,3) = WA2(I-1)*CI3+WA2(I)*CR3
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CH(I-1,K,4) = WA3(I-1)*CR4-WA3(I)*CI4
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CH(I,K,4) = WA3(I-1)*CI4+WA3(I)*CR4
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106 CONTINUE
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107 CONTINUE
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RETURN
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END
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