求分析此段JS代码

function pr_getdt1(hfurl, ch, resv, sc) {
    var d = document,
    r = d.referrer,
    suid = '-',
    c = new Date().getUTCMilliseconds(),
    m = d.cookie.match(/suid=([^;]*)(;|$)/);
    if (m) suid = m[1];
    else {
        d.cookie = "suid=" + (Math.round(Math.random() * 2147483647) * c) % 10000000000 + ";path=/; domain=zzzyk.com;expires=Sun, 18 Jan 2038 00:00:00 GMT;";
        m = d.cookie.match(/suid=([^;]*)(;|$)/);
        if (m) suid = m[1];
    }
    sc = sc || "";
    var timg = new Image(1, 1);
timg.src = " http://pr.zzzyk.com/pingd?srctype=getsret&ourl=" + escape(hfurl) + "&lurl=" + escape(d.location) + "&suid=" + suid + "&ch=" + ch + "&sort=" + resv + "&sc=" + sc + "&rand=" + Math.random();
}
function pr_get(hfurl, ch, resv, sc) {
    if ((0 == hfurl.length) || (0 == ch.length)) return;
    pr_getdt1(hfurl, ch, resv, sc);
    return;
}
function st_get(hfurl, ch, resv) {
    pr_get(hfurl, ch, resv, "web");
}