code: func (r *sampleRing) reduceDelta(delta int64) bool {
  	if delta > r.delta {
  		return false
  	}
  	r.delta = delta
  
  	if r.l == 0 {
  		return true
  	}
  
  	// Free head of the buffer of samples that just fell out of the range.
  	l := len(r.buf)
  	tmin := r.buf[r.i].t - delta
  	for r.buf[r.f].t < tmin {
  		r.f++
  		if r.f >= l {
  			r.f -= l
  		}
  		r.l--
  	}
  	return true
  }
docs: // reduceDelta lowers the buffered time delta, dropping any samples that are
  // out of the new delta range.