Finding prime numbers with Javascript

2009-10-16T00:00:00-07:00

A few days ago I introduced a friend of mine Jorge Rocha to SPOJ an online judge system for user-submitted programs, one of the first problems that he tried was the Prime Generator it consisted in finding all primes in a given range of numbers, after some time and few different algorithms he asked me if I had any tips to help him, although he had the correct algorithm (Sieve of Eratosthenes) something was clearly missing, the solution wasn’t fast enough and I had no clue where to go from there, so as usual when a question like that comes up I resort to Mauro Persano… and obviously he knew the answer, he taught us how to apply a heuristic to the algorithm to help solve the problem and after doing so the code worked and the solution was approved.

Although I’m not really into crazy algorithms challenges I thought I’d give it a try just to see how fast the solution would be in JS, note that most of the solutions submitted are in C/C++ or Java, much faster than JS and to make things worst the interpreter was Rhino, anyways we went ahead and recreated the solution in Javascript, so now it was time to test it… a little more tweaking to make it receive inputs via console and we had it running, right away we realized that our output via stdout was slowing us down, printing 10 times in a row all primes until 1 billion in the shell is not really fast but it was required to, I knew we had little or no chances to get approved but anyways we tried… and as I suspected we didn’t get approved :(, but I decided to test locally in different browsers/engines with and without output.

Here are the results, I also built a test runner so you can test on your own:

Chrome is usually the best, V8 is blazing fast but it chokes when outputting the results through WebKit
Rhino does a great job specially with a high number of runs because of JVM
Firefox runs nicely with short ranges but stops the script because of the long time running
Opera wasn’t fast but it never crashed or stopped

Browser/Engine	# of runs	Avg(ms) 0 - 100 thousand	Avg(ms) 0 - 1 million
Rhino 1.7 *	10	250	2330
Firefox 3.5.3 *	10	670	Stopped
Chrome 4.0 *	10	32	3050
Opera 10 *	10	540	4956
Rhino 1.7	100	34	304
Firefox 3.5.3	100	20	Stopped
Chrome 4.0	100	9	128
Opera 10	100	100	1213

* With output (tested under Ubuntu 9.04 Jaunty)

JavaScript Rules - sieve

Finding prime numbers with Javascript