The visualisation means next to nothing for proving it's *good*. But the visuali...

LnxPrgr3 · on June 27, 2014

If I look at it too long, I see "patterns" in the output of OS X's /dev/random too: http://codeanarchy.com/files/yarrow.png

Random doesn't always look random. To make matters worse, we're biased towards seeing patterns in noise: http://en.wikipedia.org/wiki/Clustering_illusion

praptak · on June 27, 2014

...and my repost from https://news.ycombinator.com/item?id=4821942.

A bookmarklet (paste in address bar) to show truly random and "evened out" dot distributions side by side. (Don't laugh at my Javascript):

javascript:"<html><body><canvas id=\"tutorial\" width=\"200\" height=\"200\">foo</canvas><-><canvas id=\"tutorial2\" width=\"200\" height=\"200\">foo</canvas><script>var canvas = document.getElementById('tutorial');var ctx = canvas.getContext('2d');ctx.fillStyle = \"rgb(000,0,0)\";for (var i=0;i<400;i++) {ctx.fillRect (Math.random() * 200,Math.random() * 200, 2, 2); };</script><script>var canvas = document.getElementById('tutorial2');var ctx = canvas.getContext('2d');ctx.fillStyle = \"rgb(000,0,0)\";for (var i=0;i<20;i++) for(var j=0;j<20;j++) for(k=0;k<1;k++) {ctx.fillRect (i * 10 + Math.random() * 10, j * 10 + Math.random() * 10, 2, 2); };</script></body></html>"

kyberias · on June 27, 2014

"Patterns"? Of course there are patterns. If there were no patterns, that would be suspicious. Do you claim to be able to look at a picture of a random number generator data and determine the quality based on that? You do realize that even perfectly random data may have patterns?

dasmithii · on June 27, 2014

It serves mostly as a litmus test against blatant predictability. As said above, sequential lines or otherwise obvious shapes would indicate poor randomness.

I wouldn't evaluate a generator solely on the basis of a bytemap. But these visualizations are of value.

dasmithii · on June 27, 2014

It seems to be an improvement from the notoriously poor rand() of PHP.

(not confident in the credibility of this article) http://boallen.com/assets/images/randbitmap_computer.png

ars · on June 27, 2014

It's not a PHP function, it's a C library function that PHP is using.

On Linux rand() doesn't suffer from the problem.

DanBC · on June 27, 2014

"Patterns" doesn't mean much. Repeated diagonal lines would be obviously broken.