code: func (kcp *KCP) Update() {
  	var slap int32
  
  	current := currentMs()
  	if kcp.updated == 0 {
  		kcp.updated = 1
  		kcp.ts_flush = current
  	}
  
  	slap = _itimediff(current, kcp.ts_flush)
  
  	if slap >= 10000 || slap < -10000 {
  		kcp.ts_flush = current
  		slap = 0
  	}
  
  	if slap >= 0 {
  		kcp.ts_flush += kcp.interval
  		if _itimediff(current, kcp.ts_flush) >= 0 {
  			kcp.ts_flush = current + kcp.interval
  		}
  		kcp.flush(false)
  	}
  }
docs: // Update updates state (call it repeatedly, every 10ms-100ms), or you can ask
  // ikcp_check when to call it again (without ikcp_input/_send calling).
  // 'current' - current timestamp in millisec.