mfftis.f

FFT源代码汇集（各种FFT源代码）

      SUBROUTINE MFFTIS(C,IMSX,IVSX,IESX,NMX,NVX,NEX,TABLES,IERR)
*   PURPOSE:
*       THE SAME AS MFFTIM.  IT IS A VARIANT OF MFFTIM, OPTIMIZED FOR
*       MAXIMUM PERFORMANCE ON MATRICES WHOSE FIRST DIMENSION IS
*       LESS THAN 64.
*       IT REQUIRES THAT TABLES HAS BEEN PREPARED BY A CALL TO MFFTP
*       WITH ID .NE. 0 .
*  IMPLEMENTATION:
*       THE TRANSFORMATION IS IMPLEMENTED THROUGH REPEATED CALLS TO THE
*       "BUTTERFLY" TRANSFORMATION MFFT?9; PARAMETERS OF THE "BUTTERFLY"
*       ARE COMMUNICATED THROUGH THE COMMON BLOCK MFFTPA.
*  ARGUMENTS:
*    INPUT:
*       C : ARRAY TO BE TRANSFORMED.
*       IMSX,IVSX,IESX,NMX,NVX,NEX: THESE ARGUMENTS DEFINE THE STRUCTURE
*           OF C ACCORDING TO THE DEFINITIONS ABOVE. THEY ARE UNCHANGED
*           ON OUTPUT
*       TABLES : ARRAY PREPARED BY MFFTP. IT  IS NOT CHANGED ON OUTPUT.
*                IT SHOULD BE DECLARED INTEGER TABLES(4*NM+14);
*                IT MUST BE INITIALIZED BY MFFTP BEFORE USAGE.
*    OUTPUT:
*       C : TRANSFORM OF THE ORIGINAL ARRAY; "BIT REVERSED" ORDER
*       IERR : ERROR CODE : =0 : SUCCESSFUL
*                         : =3 :  'TABLES' NOT CORRECTLY INITIALIZED
      COMPLEX C(*)
      INTEGER TABLES(-14:*)
      INTEGER IDERR,FACERR,TBERR
      PARAMETER (IDERR=1,FACERR=2,TBERR=3)
      COMMON /MFFTPA/  IMS,IVS,IES,NM,NV,NE,MX,LX,MLIM,MSTEP,LLIM,LSTEP,
     $ NUSTEP,IVLIM,ILIM,MD2LIM,LD2LIM
      SAVE IBASE
*  LOADING THE COMMON BLOCK : CONSTANTS
      IMS=IMSX
      IVS=IVSX
      IES=1
      NM=NMX
      NV=NVX
      NE=NEX
 
      IVLIM=(NV-1)*IVS
      LSTEP=IMS
*  LOADING THE COMMON BLOCK : ITERATION-DEPENDENT QUANTITIES: INITIALIZA
      LX=1
      MX=NM
 
      IBASE=(2+IMS)*NM
      IFAC=TABLES(-1)
      IF(IFAC.GT.3)THEN
        IERR=TBERR
        RETURN
      ENDIF
*..   RADIX 2 LOOP
200   CONTINUE
      DO 210 IM=1,TABLES(-14)
        MX=MX/2
        NUSTEP=LX*LSTEP
        ILIM=NUSTEP-1
        MSTEP=NUSTEP*2
        MLIM=NM*LSTEP-MSTEP
        CALL MFFTA9(C,TABLES(2*IBASE))
        LX=LX+LX
        IBASE=IBASE+NUSTEP
210   CONTINUE
      IF(IFAC.EQ.1)RETURN
*..   RADIX 3 LOOP
300   CONTINUE
      DO 310 IM=1,TABLES(-13)
        MX=MX/3
        NUSTEP=LX*LSTEP
        ILIM=NUSTEP-1
        MSTEP=NUSTEP*3
        MLIM=NM*LSTEP-MSTEP
        CALL MFFTB9(C,TABLES(2*IBASE))
        LX=LX*3
        IBASE=IBASE+NUSTEP*2
310   CONTINUE
      IF(IFAC.EQ.2)RETURN
*..   RADIX 5 LOOP
500   CONTINUE
      DO 510 IM=1,TABLES(-12)
        MX=MX/5
        NUSTEP=LX*LSTEP
        ILIM=NUSTEP-1
        MSTEP=NUSTEP*5
        MLIM=NM*LSTEP-MSTEP
        CALL MFFTC9(C,TABLES(2*IBASE))
        LX=LX*5
        IBASE=IBASE+NUSTEP*4
510   CONTINUE
      END