idx       int     // current index in buf
	CAvg      float64 // cumulative average
	prevSMA   float64
	filledBuf bool
}

func newSMA(ln int) *SMA {
	if ln <= 0 {
		ln = defaultWindowSize
	}
	return &SMA{
		buf:    make([]float64, ln),
		window: ln,
		idx:    0,
	}
}

func (s *SMA) addSample(next float64) {
	prev := s.buf[s.idx]
	s.buf[s.idx] = next

	if s.filledBuf {