# Detect prime numbers

## JavaScript performance comparison

Revision 4 of this test case created by Felix Böhm

## Preparation code

``````<script>
var arr = [7, 10, 37, 60, 373, 390, 1427, 7879, 7881];

// Code taken from http://ejohn.org/apps/learn/ by John Resig

function isPrime(num) {
var prime = num != 1; // Everything but 1 can be prime
for (var i = 2; i < num; i++) {
if (num % i == 0) {
prime = false;
break;
};
};
return prime;
};

function isPrimeCached(num) {
if (isPrimeCached.cache[num] !== null) {
return isPrimeCached.cache[num];
};
var prime = num != 1; // Everything but 1 can be prime
for (var i = 2; i < num; i++) {
if (num % i == 0) {
prime = false;
break;
};
};
isPrimeCached.cache[num] = prime;
return prime;
};
isPrimeCached.cache = {};

// By Devon Govett

function isPrimeFaster(num) {
var prime = num != 1 || num != 2;
for (var i = 3; i < num; i += 2) { //ignore even numbers > 2
if (num % i == 0) {
prime = false;
break;
}
}
return prime;
}

function isPrimeFasterCached(num) {
if (isPrimeFasterCached.cache[num] !== null) {
return isPrimeFasterCached.cache[num];
};

var prime = num != 1 || num != 2;
for (var i = 3; i < num; i += 2) { // ignore even numbers > 2
if (num % i == 0) {
prime = false;
break;
}
}

isPrimeFasterCached.cache[num] = prime;
return prime;
};
isPrimeFasterCached.cache = {};

// Code by Devon Govett — http://twitter.com/devongovett/status/20019256843, inspired by http://mths.be/ahf

function isPrimeRegex(n) {
return Array(n + 1).join('1').search(/^1?\$|^(11+?)\1+\$/) === -1;
};

function fermat(p) {
return (Math.pow(4, p) % p) === (4 % p);
}

function fermat_simplified(p) {
return (Math.pow(4, p - 1) % p) === 1;
}
</script>
``````

## Test runner

Warning! For accurate results, please disable Firebug before running the tests. (Why?)

Java applet disabled.

Testing in CCBot 2.0.0 / Other 0.0.0
Test Ops/sec
Fermat's little theorem
``````// a^(p) mod p = a mod p
var i = arr.length;
while (i--) {
fermat(arr[i]);
};``````
pending…
`isPrimeFasterCached()`
``````var i = arr.length;
while (i--) {
isPrimeFasterCached(arr[i]);
};``````
pending…
`isPrimeFaster()`
``````var i = arr.length;
while (i--) {
isPrimeFaster(arr[i]);
};``````
pending…
`isPrimeRegex()`
``````var i = arr.length;
while (i--) {
isPrimeRegex(arr[i]);
};``````
pending…
`isPrimeCached()`
``````var i = arr.length;
while (i--) {
isPrimeCached(arr[i]);
};``````
pending…
`isPrime()`
``````var i = arr.length;
while (i--) {
isPrime(arr[i]);
};``````
pending…
Fermat's little theorem simplified
``````// a^(p-1) mod p = 1
var i = arr.length;
while (i--) {
fermat_simplified(arr[i]);
};``````
pending…

## Revisions

You can edit these tests or add even more tests to this page by appending `/edit` to the URL.