Convert the IP address to a decimal integer

The Java IP address is converted to a long integer;
Public class util {

/**
* Convert string IP address to long
* @ Param string IP Address

* Weighted by the Left shift operation, the right of the first segment is the 24 power of 2,
The second segment has the 16 power of 2,
The right of the third paragraph is the 8th power of 2,
The right of the last segment is 1.

* @ Return
*/
Public static long getstringiptolong (string IP ){
String [] IPS = IP. Split ("[.]");
Long num = 16777216l * long. parselong (IPS [0]) +
65536l * long. parselong (IPS [1]) + 256 * long. parselong (IPS [2]) +
Long. parselong (IPS [3]);
Return num;
}

/**
* Convert a long integer IP address to a string
* @ Param long type IP Address
* @ Return
*/
Public static string getlongiptostring (long iplong ){

Long mask [] = {0x000000ff, 0x0000ff00, 0x00ff0000, 0xff000000 };
Long num = 0;
Stringbuffer ipinfo = new stringbuffer ();
For (INT I = 0; I <4; I ++ ){
Num = (iplong & Mask [I])> (I * 8 );
If (I> 0) ipinfo. insert (0 ,".");
Ipinfo. insert (0, long. tostring (Num, 10 ));
}
Return ipinfo. tostring ();
}
}

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The above is extracted from the Internet. The algorithm is unclear. Which expert can help explain it?