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Sieve of Eratosthenes
function(
a, // Check for primes in the range from 1 to 'a'
b, // Array holding numbers as key and primeness as value
c, // Placeholder
d // Placeholder
){
b=[]; // Initialize array
for(c=1;c<a;b[++c]=1); // Initialize with all numbers being 1 (prime)
for(c=2;c<=Math.sqrt(a);c++) // Loop through all numbers <= sqrt of the range to check
for(d=c;b[c]&&d<=a-c;b[d+=c]=0); // Delete all multiples of the current number as these can't be prime
// Only consider numbers marked as prime (b[c]&&)
return b // Return the sieved array
}
function(a,b,c,d){b=[];for(c=1;c<a;b[++c]=1);for(c=2;c<=Math.sqrt(a);c++)for(d=c;b[c]&&d<=a-c;b[d+=c]=0);return b}
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
Version 2, December 2004
Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE>
Everyone is permitted to copy and distribute verbatim or modified
copies of this license document, and changing it is allowed as long
as the name is changed.
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. You just DO WHAT THE FUCK YOU WANT TO.
{
"name": "sieveOfEratosthenes",
"description": "Simple implementation of the Sieve of Eratosthenes to find prime numbers.",
"keywords": [
"prime",
"number",
"math"
]
}
<!DOCTYPE html>
<title>Sieve of Eratosthenes</title>
<div>Expected value (Primes between 1 and 100): <b>2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97</b></div>
<div>Actual value (Primes between 1 and 100): <b id="result"></b></div>
<script>
var sieveOfEratosthenes = function(a,b,c,d){b=[];for(c=1;c<a;b[++c]=1);for(c=2;c<=Math.sqrt(a);c++)for(d=c;b[c]&&d<=a-c;b[d+=c]=0);return b}
var sieved = sieveOfEratosthenes(100);
var result = "";
for (i = 1; i <= 100; i++)
if (sieved[i])
result += i+', ';
document.getElementById("result").innerHTML = result.substring(0, result.length-2);
</script>
@gomfunkel

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@gomfunkel gomfunkel commented Oct 8, 2012

Saved some bytes by flooring the sqrt using "0|" instead of ceiling it with "Math.ceil()" which is not necessary. Additionally sped up the sieving by only considering numbers still marked as prime when eliminating multiples.

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@gomfunkel gomfunkel commented Oct 8, 2012

Hmm, actually it isn't even necessary to floor the sqrt...

@atk

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@atk atk commented Oct 9, 2012

Instead of if, you can put the testing of b[c] inside the last for loop, saving 2 bytes:

function(a,b,c,d){b=[];for(c=1;c<a;b[++c]=1);for(c=2;c<=Math.sqrt(a);c++)for(d=c;b[c]&&d<=a-c;b[d+=c]=0);return b}

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@gomfunkel gomfunkel commented Oct 9, 2012

@atk Nice, thanks!

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@atk atk commented Oct 10, 2012

You're welcome, @gomfunkel

@neizod

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@neizod neizod commented Oct 13, 2012

subscript.

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