UUID有多独特?

Math.log2 = Math.log2 || function(n){ return Math.log(n) / Math.log(2); }
Math.trueRandom = (function() {
var crypt = window.crypto || window.msCrypto;


if (crypt && crypt.getRandomValues) {
// if we have a crypto library, use it
var random = function(min, max) {
var rval = 0;
var range = max - min;
if (range < 2) {
return min;
}


var bits_needed = Math.ceil(Math.log2(range));
if (bits_needed > 53) {
throw new Exception("We cannot generate numbers larger than 53 bits.");
}
var bytes_needed = Math.ceil(bits_needed / 8);
var mask = Math.pow(2, bits_needed) - 1;
// 7776 -> (2^13 = 8192) -1 == 8191 or 0x00001111 11111111


// Create byte array and fill with N random numbers
var byteArray = new Uint8Array(bytes_needed);
crypt.getRandomValues(byteArray);


var p = (bytes_needed - 1) * 8;
for(var i = 0; i < bytes_needed; i++ ) {
rval += byteArray[i] * Math.pow(2, p);
p -= 8;
}


// Use & to apply the mask and reduce the number of recursive lookups
rval = rval & mask;


if (rval >= range) {
// Integer out of acceptable range
return random(min, max);
}
// Return an integer that falls within the range
return min + rval;
}
return function() {
var r = random(0, 1000000000) / 1000000000;
return r;
};
} else {
// From http://baagoe.com/en/RandomMusings/javascript/
// Johannes Baagøe <baagoe@baagoe.com>, 2010
function Mash() {
var n = 0xefc8249d;


var mash = function(data) {
data = data.toString();
for (var i = 0; i < data.length; i++) {
n += data.charCodeAt(i);
var h = 0.02519603282416938 * n;
n = h >>> 0;
h -= n;
h *= n;
n = h >>> 0;
h -= n;
n += h * 0x100000000; // 2^32
}
return (n >>> 0) * 2.3283064365386963e-10; // 2^-32
};


mash.version = 'Mash 0.9';
return mash;
}


// From http://baagoe.com/en/RandomMusings/javascript/
function Alea() {
return (function(args) {
// Johannes Baagøe <baagoe@baagoe.com>, 2010
var s0 = 0;
var s1 = 0;
var s2 = 0;
var c = 1;


if (args.length == 0) {
args = [+new Date()];
}
var mash = Mash();
s0 = mash(' ');
s1 = mash(' ');
s2 = mash(' ');


for (var i = 0; i < args.length; i++) {
s0 -= mash(args[i]);
if (s0 < 0) {
s0 += 1;
}
s1 -= mash(args[i]);
if (s1 < 0) {
s1 += 1;
}
s2 -= mash(args[i]);
if (s2 < 0) {
s2 += 1;
}
}
mash = null;


var random = function() {
var t = 2091639 * s0 + c * 2.3283064365386963e-10; // 2^-32
s0 = s1;
s1 = s2;
return s2 = t - (c = t | 0);
};
random.uint32 = function() {
return random() * 0x100000000; // 2^32
};
random.fract53 = function() {
return random() +
(random() * 0x200000 | 0) * 1.1102230246251565e-16; // 2^-53
};
random.version = 'Alea 0.9';
random.args = args;
return random;


}(Array.prototype.slice.call(arguments)));
};
return Alea();
}
}());


Math.guid = function() {
return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c)    {
var r = Math.trueRandom() * 16 | 0,
v = c == 'x' ? r : (r & 0x3 | 0x8);
return v.toString(16);
});
};
function logit(item1, item2) {
console.log("Do "+item1+" and "+item2+" equal? "+(item1 == item2 ? "OMG! take a screenshot and you'll be epic on the world of cryptography, buy a lottery ticket now!":"No they do not. shame. no fame")+ ", runs: "+window.numberofRuns);
}
numberofRuns = 0;
function test() {
window.numberofRuns++;
var x = Math.guid();
var y = Math.guid();
var test = x == y || historyTest(x,y);


logit(x,y);
return test;


}
historyArr = [];
historyCount = 0;
function historyTest(item1, item2) {
if(window.luckyDog) {
return false;
}
for(var i = historyCount; i > -1; i--) {
logit(item1,window.historyArr[i]);
if(item1 == history[i]) {
            

return true;
}
logit(item2,window.historyArr[i]);
if(item2 == history[i]) {
            

return true;
}


}
window.historyArr.push(item1);
window.historyArr.push(item2);
window.historyCount+=2;
return false;
}
luckyDog = false;
document.body.onload = function() {
document.getElementById('runit').onclick  = function() {
window.luckyDog = document.getElementById('lucky').checked;
var val = document.getElementById('input').value
if(val.trim() == '0') {
var intervaltimer = window.setInterval(function() {
var test = window.test();
if(test) {
window.clearInterval(intervaltimer);
}
},0);
}
else {
var num = parseInt(val);
if(num > 0) {
var intervaltimer = window.setInterval(function() {
var test = window.test();
num--;
if(num < 0 || test) {
    

window.clearInterval(intervaltimer);
}
},0);
}
}
};
};

Please input how often the calulation should run. set to 0 for forever. Check the checkbox if you feel lucky.<BR/>
<input type="text" value="0" id="input"><input type="checkbox" id="lucky"><button id="runit">Run</button><BR/>