code: func FFTShiftF(buffer []float64) []float64 {
  	var tmp float64
  	size := len(buffer) / 2
  	for i := 0; i < size; i++ {
  		tmp = buffer[i]
  		buffer[i] = buffer[size+i]
  		buffer[size+i] = tmp
  	}
  	return buffer
  }
docs: // FFTShiftF shifts a buffer of floats. The passed buffer is modified.
  // See http://www.mathworks.com/help/matlab/ref/fftshift.html