看了这节课，不知道下面这段配置该如何解释了？

location / {
    access_log /usr/work/tool/log/webserver/os-app-api.log main;
   set $flag 0;
   if ( $host = "taohui.com" ) {
        set $flag "${flag}1";
   }
   if ( $uri != "/pc/index") {
        set $flag "${flag}2";
    }
    if ( $uri != "/") {
        set $flag "${flag}3";
    }
   if ( $flag = "0123") {
        rewrite "^/(.*)$" https://www.baidu.com permanent;
   }
    if ( $uri = "/d") {
        set $flag "${flag}5";
    }
   if ( $flag = "015") {
        rewrite "^/(.*)$" https://www.google.com;
   }
}