How to generate third field in _ga and _gid? - cookies

Question

I'm investigate too much on _gid and _ga. And as i know, the definition of them:
_ga: used to identify unique users and it expires after 2 years.
_gid: used to identify unique users and it expires after 24 hours.
Example:
_ga: GA1.3.292651669.1502954402
_gid: GA1.3.974792242.1509957189
From what are the values in _ga cookie?, I know the meaning of each filed in _ga. And it's the same for _gid.
But I don't know how to generate third field, random generated user ID(for _ga:292651669 and for _gid: 974792242).
I tried to delete both _ga & _gid and I get the new couple _ga: GA1.3.2097663971.1509959880 and _gid: GA1.3.1180999143.1509959880. The third fields of both are changed. So how can they generate and how google identify user by them. Assumption I open browser today with a couple of _gid and _ga, and tomorrow, I cleared all cookies, ga will create of new couplw (_gid,_ga).; It means I'm in today that different tomorrow's me.
Please help me.
Thanks & Best Regards,
Jame

Answer 1

Here is the code from analytics.js release 2017-09-21 that generates the random id.
It's a random value based on current time, userAgent, cookie, referrer and history.length from the window object.
var O = window;
// var M = document;
// Stack Overflow doesn't allow cookie access in sandbox, so lets fake it:
var M = [];
M.cookie = "cookieName=someValue";
var hd = function() {
return Math.round(2147483647 * Math.random())
}
function La(a) {
var b = 1, c;
if (a)
for (b = 0,
c = a.length - 1; 0 <= c; c--) {
var d = a.charCodeAt(c);
b = (b << 6 & 268435455) + d + (d << 14);
d = b & 266338304;
b = 0 != d ? b ^ d >> 21 : b
}
return b
}
var ra = function() {
for (var a = O.navigator.userAgent + (M.cookie ? M.cookie : "") + (M.referrer ? M.referrer : ""), b = a.length, c = O.history.length; 0 < c; )
a += c-- ^ b++;
return [hd() ^ La(a) & 2147483647, Math.round((new Date).getTime() / 1E3)].join(".")
}
document.getElementById('output').innerText = ra();
<h3>Output:</h3>
<pre id="output"></pre>