42 lines
1.2 KiB
JavaScript
42 lines
1.2 KiB
JavaScript
function primeGenerator(num, showPrimes) {
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var i,
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arr = [];
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function isPrime(num) {
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// try primes <= 16
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if (num <= 16) return (
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num == 2 || num == 3 || num == 5 || num == 7 || num == 11 || num == 13
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);
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// cull multiples of 2, 3, 5 or 7
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if (num % 2 == 0 || num % 3 == 0 || num % 5 == 0 || num % 7 == 0)
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return false;
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// cull square numbers ending in 1, 3, 7 or 9
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for (var i = 10; i * i <= num; i += 10) {
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if (num % (i + 1) == 0) return false;
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if (num % (i + 3) == 0) return false;
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if (num % (i + 7) == 0) return false;
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if (num % (i + 9) == 0) return false;
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}
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return true;
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}
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if (typeof num == "number") {
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for (i = 0; arr.length < num; i++) if (isPrime(i)) arr.push(i);
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// first x primes
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if (showPrimes) return arr;
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// xth prime
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else return arr.pop();
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}
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if (Array.isArray(num)) {
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for (i = num[0]; i <= num[1]; i++) if (isPrime(i)) arr.push(i);
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// primes between x .. y
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if (showPrimes) return arr;
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// number of primes between x .. y
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else return arr.length;
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}
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// throw a default error if nothing returned yet
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// (surrogate for a quite long and detailed try-catch-block anywhere before)
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throw("Invalid arguments for primeGenerator()");
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}
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