2016-01-23 13:28:10 +03:00
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<!DOCTYPE html>
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<html>
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<head>
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<title>How many bit-reversed primes are prime?</title>
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</head>
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<body>
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<pre>
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<script>
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var start = new Date().getTime();
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// Add the lpad method to Strings, for adding left padding
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String.prototype.lpad = function(padString, length) {
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var str = this;
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while (str.length < length)
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str = padString + str;
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return str;
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}
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// Naive prime checker
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function is_prime(n)
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{
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for (var i = 2; i <= n/2; i++) {
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if (n % i === 0) {
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return false;
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}
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}
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2016-01-23 20:44:13 +03:00
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if (n === 1) {
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return false;
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}
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2016-01-23 13:28:10 +03:00
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return true;
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}
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// Bit reversal
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function bit_reverse(num)
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{
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var rev = 0;
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while (num > 0) {
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rev <<= 1;
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rev |= (num & 1);
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num >>= 1;
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}
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return rev;
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}
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for (var num = 1; num < 10000; num++) {
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var rev = bit_reverse(num);
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var num_prime = is_prime(num);
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var rev_prime = is_prime(rev);
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document.write(num.toString().lpad(" ", 7) + " ");
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document.write(num_prime ? "Prime" : " ");
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document.write(" ");
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document.write(rev.toString().lpad(" ", 7) + " ");
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document.write(rev_prime ? "Prime" : " ");
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document.write(" ");
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document.write(num_prime && rev_prime ? "(both)" : "");
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document.write("\n");
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}
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var end = new Date().getTime();
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var time = end - start;
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document.write('Execution time: ' + time + '\n');
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</script>
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</pre>
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</body>
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</html>
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