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Sieve of Eratosthenes
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| scrolling: yes | |
| border: no | |
| license: MIT | |
| height: 960 |
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| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <script src="https://d3js.org/d3.v4.min.js"></script> | |
| <body> | |
| <p id="time"></p> | |
| </body> | |
| <script> | |
| // From Mathematics to Generic Programming, p. 27. | |
| var worker = new Worker("./worker.js"); | |
| // Compute prime less than 100,000. | |
| worker.postMessage({ n: 100000}); | |
| worker.onmessage = function(event) { | |
| switch (event.data.type) { | |
| case "end": return ended(event.data); | |
| } | |
| }; | |
| // Render computed primes when the Web Worker is done. | |
| function ended(data) { | |
| d3.select("#time") | |
| .style("margin-left", "5px") | |
| .style("font-size", "14px") | |
| .style("color", "#aaa") | |
| .style("font-family", "helvetica") | |
| .html("Sifted " + d3.format(",")(data.values.length) + " primes in " + data.elapsed + " ms"); | |
| d3.select("body").append("p") | |
| .datum(data.values) | |
| .html(function(d) { return d.join(" "); }) | |
| .style("margin", "0 auto") | |
| .style("font-size", "18px") | |
| .style("font-family", "helvetica") | |
| .style("line-height", "1.4em") | |
| .style("width", "720px"); | |
| } | |
| </script> |
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| onmessage = function(event) { | |
| var n = event.data.n, | |
| startTime = Date.now(), | |
| endTime; | |
| var computedPrimes = primes(n); | |
| endTime = Date.now(); | |
| postMessage({ | |
| type: "end", | |
| values: computedPrimes, | |
| elapsed: endTime - startTime | |
| }); | |
| } | |
| // Returns an array containing the primes less than or equal to n. | |
| function primes(n) { | |
| var sieve = new Array(Math.ceil(index(n))); | |
| sieve.fill(true); | |
| sift(sieve); | |
| return sieve.reduce(function(accumulator, current, i, array) { | |
| if (current) accumulator.push(value(i)); | |
| return accumulator; | |
| }, [2]); | |
| } | |
| function sift(sieve) { | |
| var i = 0, | |
| squaredIndex = 3, | |
| factor = 3; | |
| while (squaredIndex < sieve.length) { | |
| if (sieve[i]) { | |
| markSieve(sieve, squaredIndex, value(i)); | |
| } // else all multiples of this factor have been crossed out | |
| i++; | |
| squaredIndex += factor; | |
| factor += 2; // e.g., 3 -> 5 -> 7 -> 9 | |
| squaredIndex += factor; // squredIndex += factor(i) + factor(i + 1) | |
| } | |
| return sieve; | |
| } | |
| // Mark boolean sieve false for all multiples of the | |
| // given factor. | |
| function markSieve(sieve, begin, factor) { | |
| var i, n; | |
| for (i = begin, n = sieve.length; i < n - factor; i += factor) { | |
| sieve[i] = false; | |
| } | |
| } | |
| // Returns the value of a number in the sieve containing only | |
| // odd numbers and starting at 3. | |
| function value(i) { | |
| return i + i + 3; | |
| } | |
| // Returns the index for a value in the sieve containing only | |
| // odd numbers and starting at 3. | |
| function index(v) { | |
| return (v - 3) / 2; | |
| } |
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