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Entropy library assumes cards are discarded

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and removed the duplicate logic from the UI logic.
This commit is contained in:
Ian Coleman
2016-11-17 14:28:26 +11:00
parent bbc29c80f4
commit 6422c1cd57
3 changed files with 81 additions and 67 deletions
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src/js/entropy.js
+46
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@@ -117,6 +117,40 @@ window.Entropy = new (function() {
while (entropyBin.length < expectedBits) {
entropyBin = "0" + entropyBin;
}
// Assume cards are NOT replaced.
// Additional entropy decreases as more cards are used. This means
// entropy is measured using n!, not base^n.
// eg the second last card can be only one of two, not one of fifty two
// so the added entropy for that card is only one bit at most
if (base.asInt == 52) {
// Get the maximum value without replacement
var totalDecks = Math.ceil(base.parts.length / 52);
var totalCards = totalDecks * 52;
var totalCombos = factorial(52).pow(totalDecks);
var totalRemainingCards = totalCards - base.parts.length;
var remainingDecks = Math.floor(totalRemainingCards / 52);
var remainingCards = totalRemainingCards % 52;
var remainingCombos = factorial(52).pow(remainingDecks).multiply(factorial(remainingCards));
var currentCombos = totalCombos.divide(remainingCombos);
var numberOfBits = Math.log2(currentCombos);
var maxWithoutReplace = BigInteger.pow(2, numberOfBits);
// aggresive flooring of numberOfBits by BigInteger.pow means a
// more accurate result can be had for small numbers using the
// built-in Math.pow function.
if (numberOfBits < 32) {
maxWithoutReplace = BigInteger(Math.round(Math.pow(2, numberOfBits)));
}
// Get the maximum value with replacement
var maxWithReplace = BigInteger.pow(52, base.parts.length);
// Calculate the new value by scaling the original value down
var withoutReplace = entropyInt.multiply(maxWithoutReplace).divide(maxWithReplace);
// Left pad with zeros based on number of bits
var entropyBin = withoutReplace.toString(2);
var numberOfBitsInt = Math.floor(numberOfBits);
while (entropyBin.length < numberOfBitsInt) {
entropyBin = "0" + entropyBin;
}
}
// Supply a 'filtered' entropy string for display purposes
var entropyClean = base.parts.join("");
var entropyHtml = base.parts.join("");
@@ -221,4 +255,16 @@ window.Entropy = new (function() {
return BigInteger.log(x) / BigInteger.log(2);
};
// Depends on BigInteger
function factorial(n) {
if (n == 0) {
return 1;
}
f = BigInteger.ONE;
for (var i=1; i<=n; i++) {
f = f.multiply(new BigInteger(i));
}
return f;
}
})();