What is the logic of this MFC custom message mapping function?

Today read a custom message function modify packet sending command, download file command number is 4, did not quite understand the logic of the bit operation here. "4< < 1 | 0 "

//int ret = SendCommandPacket(4, false, (BYTE*)(LPCTSTR)strFile, strFile.GetLength());    //修改前
    int ret = SendMessageA(WM_SEND_PACKET, 4 << 1 | 0, (LPARAM)(LPCSTR)strFile);   //用自定义消息函数发送下载文件命令
......

#define WM_SEND_PACKET (WM_USER + 1) 
//自定义消息响应函数
/*用位运算合并参数*/

LRESULT CRemoteControlClientDlg::OnSendPacket(WPARAM wParam, LPARAM lParam)
{
    int ret = 0;
    int cmd = wParam >> 1;
    switch (cmd) 
    {
case 4: //下载文件
    {
        CString strFile = (LPCTSTR)lParam;
        ret = SendCommandPacket(cmd, wParam & 1,
            (BYTE*)(LPCTSTR)strFile, strFile.GetLength());
    }
            break;
    case 6://截取屏幕
    {
        ret = SendCommandPacket(cmd, wParam & 1);
    }
            break;
    default:
        ret = -1;
    }
    return ret;
}