mirror of
https://github.com/JasonYANG170/IOTConnect-Web.git
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46 lines
2.3 KiB
JavaScript
46 lines
2.3 KiB
JavaScript
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/*
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* The value of the constant Number.MAX_SAFE_INTEGER equals (2 ** 53 - 1) but it
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* is fairly new.
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*/
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const MAX_SAFE_INTEGER = Number.MAX_SAFE_INTEGER === undefined ? 9007199254740991 : Number.MAX_SAFE_INTEGER;
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const TWO_TO_THE_POWER_OF_TWENTY_NINE = 536870912;
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const TWO_TO_THE_POWER_OF_THIRTY = TWO_TO_THE_POWER_OF_TWENTY_NINE * 2;
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export const createGenerateUniqueNumber = (cache, lastNumberWeakMap) => {
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return (collection) => {
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const lastNumber = lastNumberWeakMap.get(collection);
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/*
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* Let's try the cheapest algorithm first. It might fail to produce a new
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* number, but it is so cheap that it is okay to take the risk. Just
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* increase the last number by one or reset it to 0 if we reached the upper
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* bound of SMIs (which stands for small integers). When the last number is
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* unknown it is assumed that the collection contains zero based consecutive
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* numbers.
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*/
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let nextNumber = lastNumber === undefined ? collection.size : lastNumber < TWO_TO_THE_POWER_OF_THIRTY ? lastNumber + 1 : 0;
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if (!collection.has(nextNumber)) {
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return cache(collection, nextNumber);
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}
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/*
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* If there are less than half of 2 ** 30 numbers stored in the collection,
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* the chance to generate a new random number in the range from 0 to 2 ** 30
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* is at least 50%. It's benifitial to use only SMIs because they perform
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* much better in any environment based on V8.
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*/
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if (collection.size < TWO_TO_THE_POWER_OF_TWENTY_NINE) {
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while (collection.has(nextNumber)) {
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nextNumber = Math.floor(Math.random() * TWO_TO_THE_POWER_OF_THIRTY);
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}
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return cache(collection, nextNumber);
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}
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// Quickly check if there is a theoretical chance to generate a new number.
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if (collection.size > MAX_SAFE_INTEGER) {
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throw new Error('Congratulations, you created a collection of unique numbers which uses all available integers!');
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}
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// Otherwise use the full scale of safely usable integers.
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while (collection.has(nextNumber)) {
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nextNumber = Math.floor(Math.random() * MAX_SAFE_INTEGER);
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}
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return cache(collection, nextNumber);
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};
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};
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//# sourceMappingURL=generate-unique-number.js.map
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