Обратное преобразование Фурье (IFFT)

procedure TFFTBase.InitMem(WindowSize: Integer);
begin
 fWindowSize:=WindowSize;
 tTlbSize:=(2*fWindowSize+1)*SizeOf(Single);
 fSinTbl:=AllocMem(tTlbSize);
 fCosTbl:=AllocMem(tTlbSize);
end;
 
procedure TFFTBase.InitSinCosTbl;
var i :integer;
begin
 for i :=1 to 2*fWindowSize do begin
  fSinTbl[i] := (-1)*Sin(PI/i);
  fCosTbl[i] := Cos(PI/i);
 end;
end;
 
 NV2 :=N shr 1;
 NM1 :=N-1;
 J   :=1;
 if Inverse then
  for i :=0 to N-1 do
   TComplexArray(F^)[i].Im :=-TComplexArray(F^)[i].Im;
 
 for I :=1 to NM1 do begin
  if I<J then begin
   T      :=TComplexArray(F^)[J-1];
   TComplexArray(F^)[J-1] :=TComplexArray(F^)[I-1];
   TComplexArray(F^)[I-1] :=T;
  end;
  K :=NV2;
  while K < J do begin
   J :=J - K;
   K :=K shr 1;
  end;
  J :=J + K;
 end;
 for L :=1 to M do begin
  LE   :=2 shl (L-1);
  LE1  :=LE shr 1;
  U.Re :=1.0; U.Im :=0.0;
  W.Re :=fCosTbl[LE1];
  W.Im :=fSinTbl[LE1];
  for J :=1 to LE1 do begin
   I :=J;
   while I <= N do begin
    IP :=I + LE1;
    T.Re    :=TComplexArray(F^)[IP-1].Re * U.Re - TComplexArray(F^)[IP-1].Im * U.Im;
    T.Im    :=TComplexArray(F^)[IP-1].Re * U.Im + TComplexArray(F^)[IP-1].Im * U.Re;
    TComplexArray(F^)[IP-1].Re :=TComplexArray(F^)[I-1].Re - T.Re;
    TComplexArray(F^)[IP-1].Im :=TComplexArray(F^)[I-1].Im - T.Im;
    TComplexArray(F^)[I-1].Re:=TComplexArray(F^)[I-1].Re+T.Re;
    TComplexArray(F^)[I-1].Im:=TComplexArray(F^)[I-1].Im+T.Im;
    Inc(I,LE);
   end;
   Uo :=U;
   U.Re :=(Uo.Re * W.Re) - (Uo.Im * W.Im);
   U.Im :=(Uo.Re * W.Im) + (Uo.Im * W.Re);
  end;
 end;
 
 ImDummy :=1/Sqrt(N);
 if Inverse then ImDummy :=-ImDummy;
 ReDummy :=Abs(ImDummy);
 for I :=1 to N do
  begin
   TComplexArray(F^)[i-1].Re :=TComplexArray(F^)[i-1].Re*ReDummy;
   TComplexArray(F^)[i-1].Im :=TComplexArray(F^)[i-1].Im*ImDummy;
  end;
 
 DelMem; 
end;