FUNCTION test_idlfft


; ---------
; Open file
; ---------

  OPENR, 1, 'fft_input.dat'


; ------------------
; Read in input data
; ------------------

  file_info = FSTAT( 1 )
  n         = ( file_info.size / 4 ) / 2
  MESSAGE, STRING( n ) + ' real and imaginary points to be read', /INFO

  real_part = FLTARR( n )
  imag_part = FLTARR( n )

  READU, 1, real_part, imag_part
  CLOSE, 1


; ------------
; Reflect data
; ------------

  real_part = [ real_part, REVERSE( real_part[ 1 : n - 2 ] ) ]
  imag_part = [ imag_part, -1.0 * REVERSE( imag_part[ 1 : n - 2 ] ) ]


; --------------------------------------
; Perform FFT; spectrum -> interferogram
; --------------------------------------

  cxs = COMPLEX( real_part, imag_part )
  ifg = FFT( cxs, /INVERSE )


; -------------
; Output result
; -------------

  OPENW, 1, 'idlfft_output.dat'
  WRITEU, 1, FLOAT( ifg ), IMAGINARY( ifg )
  CLOSE, 1


; -------------
; Return result
; -------------

  RETURN, ifg

END