code: func (dec *fecDecoder) freeRange(first, n int, q []fecPacket) []fecPacket {
  	for i := first; i < first+n; i++ { // recycle buffer
  		xmitBuf.Put([]byte(q[i]))
  	}
  
  	if first == 0 && n < len(q)/2 {
  		return q[n:]
  	}
  	copy(q[first:], q[first+n:])
  	return q[:len(q)-n]
  }
docs: // free a range of fecPacket