mfftb7.f

FFT源代码汇集（各种FFT源代码）

      SUBROUTINE MFFTB7(C,FAC)
*
*   PURPOSE:
*       ELEMENTARY COOLEY-TUKEY RADIX 3 STEP APPLIED TO A VECTOR-OF
*       2-VECTORS-OF-COMPLEX C[IMS,NM [IVS,NV [IES,NE]]].
*       SEE REF.[1] FOR NOTATIONS.
*       THIS ROUTINE CAN BE USED ONLY BY ROUTINE MFFTIM, WHICH CONTROLS
*       ITS OPERATION THROUGH THE MFFTPA COMMON
*
*   DUMMY ARGUMENTS :
*
*   C   ARRAY BEING FOURIER  TRANSFORMED
*   FAC PHASE FACTORS, PREPARED BY MFFTP; NOT MODIFIED IN OUTPUT
*
      COMMON /MFFTPA/  IMS,IVS,IES,NM,NV,NE,MX,LX,MLIM,MSTEP,LLIM,LSTEP,
     $ NUSTEP,IVLIM,ILIM,MD2LIM,LD2LIM
      INTEGER NUSTEP
      COMPLEX C(0:NUSTEP-1,0:2),FAC(0:*)
      COMPLEX T0,T1,T2,F1,F2
      REAL SIN60
      PARAMETER ( SIN60 =  8.6602540378443864E-1)
*..  LAM>0
          LAMF=MX
          DO 100 LAM=LSTEP,LLIM,LSTEP
            F1=FAC(LAMF)
            F2=FAC(LAMF*2)
            DO 90 MU=LAM,LAM+MLIM,MSTEP
              DO 80 IV=MU,MU+IVLIM,IVS
              DO 80 I=IV,IV+ILIM,IES
                T0=C(I,1)*F1+C(I,2)*F2
                T2=(C(I,1)*F1-C(I,2)*F2)*SIN60
                T1=C(I,0)-0.5*T0
                C(I,0)=C(I,0)+T0
                C(I,1)=(T1+CMPLX(-AIMAG(T2),REAL(T2)))
                C(I,2)=(T1-CMPLX(-AIMAG(T2),REAL(T2)))
80            CONTINUE
90          CONTINUE
            LAMF=LAMF+MX
100       CONTINUE
          DO 92 MU=0,MLIM,MSTEP
            DO 82 IV=MU,MU+IVLIM,IVS
            DO 82 I=IV,IV+ILIM,IES
                T0=C(I,1)+C(I,2)
                T2=(C(I,1)-C(I,2))*SIN60
                T1=C(I,0)-0.5*T0
                C(I,0)=C(I,0)+T0
                C(I,1)=(T1+CMPLX(-AIMAG(T2),REAL(T2)))
                C(I,2)=(T1-CMPLX(-AIMAG(T2),REAL(T2)))
82          CONTINUE
92        CONTINUE
      END