sw/rescue/lab8e_goettingen/disk2_11/rkb/paroff/fftc.ft

   1 C       FFTC.FT   FFT-V4A   4/22/76
   2
   3         SUBROUTINE FFTC (A,N,M,SGNEX)
   4
   5 C-------FFT VON N=2**M KOMPLEXEN DATEN
   6 C       A = IN- UND OUTPUTARRAY, LAENGE N=2**M, KOMPLEX
   7 C-------SGNEXP = VORZEICHEN DES EXPONENTEN DER E-FUNKTIONEN
   8
   9         DIMENSION A(2,513)
  10         DIMENSION U(2),W(2),T(2),V(2)
  11         NV2=N/2
  12         NM1=N-1
  13         J=1
  14         DO 7 I=1,NM1
  15         IF (I.GE.J) GOTO 5
  16         T(1)=A(1,J)
  17         T(2)=A(2,J)
  18         A(1,J)=A(1,I)
  19         A(2,J)=A(2,I)
  20         A(1,I)=T(1)
  21         A(2,I)=T(2)
  22 5       K=NV2
  23 6       IF (K.GE.J) GOTO 7
  24         J=J-K
  25         K=K/2
  26         GO TO 6
  27 7       J=J+K
  28         PI=3.141592653*SGNEX
  29         LE1=1
  30         S=0.
  31         DO 30 L=1,M
  32         LE=2*LE1
  33         U(1)=1.
  34         U(2)=0.
  35         SN=SIN(PI/FLOAT(LE))
  36         W(1)=-2.*SN*SN
  37         W(2)=S
  38         S=SN
  39         DO 20 J=1,LE1
  40         DO 10 I=J,N,LE
  41         IP=I+LE1
  42         T(1)=A(1,IP)*U(1)-A(2,IP)*U(2)
  43         T(2)=A(1,IP)*U(2)+A(2,IP)*U(1)
  44         A(1,IP)=A(1,I)-T(1)
  45         A(2,IP)=A(2,I)-T(2)
  46         A(1,I)=A(1,I)+T(1)
  47         A(2,I)=A(2,I)+T(2)
  48 10      CONTINUE
  49         V(1)=U(1)+U(1)*W(1)-U(2)*W(2)
  50         V(2)=U(2)+U(1)*W(2)+U(2)*W(1)
  51         U(1)=V(1)
  52         U(2)=V(2)
  53         COR=.5-.5*(U(1)*U(1)+U(2)*U(2))
  54         U(1)=COR*U(1)+U(1)
  55 20      U(2)=COR*U(2)+U(2)
  56 30      LE1=LE
  57         RETURN
  58         END
  59 \f\1a