A good random number generator for C

Question

I need a good random number generator for a program I'm writing in C. It's a fractal flame generator, if you're interested. My images were coming out very grainy, even though I had success with the same algorithm in the past. The difference, I finally realized, was the random number generator I was using. Incredibly, it makes an ENORMOUS difference. I'm hoping that an even better random number generator might yield better results. The answer could come in the form of a code sample or a link to a pre-existing random number library. The most important requirements:

• it should produce relatively high quality streams of random numbers
• its period must be over ten billion
• it should be fast enough and offer a good performance trade-off.

Rosannarosanne

en.wikipedia.org/wiki/… – Subalpine

this question is valid IMHO. A bit too selft centered, but still valid in the requirements. – Derna

@Derna I nominated this question for reopening. I can't see why this is "not a real question". Not a good question? Maybe, but it's still a valid one. – Autograft

rand() is a pretty good random number generator in C. – Hushaby

Woah... I didn't expect such a negative response. I don't understand this community and it's somewhat rigid rules sometimes. In my opinion, this is a perfectly valid question. It has specific points that an answer must meet so it's not too general, it gives some context, so answers can be made specific to the situation, it isn't so specific that it won't ever be useful to anyone again. I know I'm not supposed to, but I'm beginning to take this a bit personally. It seems like I get attacked a lot on this site. – Rosannarosanne

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Answer 1

This seems like a good use-case for the Mersenne Twister

• It's faster than most standard implementations of rand()
• It has a very long (2^19937 − 1) period
• It has a pretty high quality - it passes most standardized randomness tests
• It's public domain

Autograft

no, he is giving a candidate. +1 btw, never heard of Mersenne before – Derna

Wow, this looks like a REALLY good random number generator. Thanks so much Philipp, I would never have found this on my own. – Rosannarosanne

I'm surprised that MT is faster than most implementations of rand(). Isn't rand() commonly an LCG, hence very fast but poor quality? – Pitterpatter

Considering the fact that this actually turned my non-working rand()-based algorithm into something I could actually work with, +1! – Stearoptene

Answer 2

If you are looking for a very fast, decent quality algorithm, you should think about xorshift128+ or xorshift1024*. They are almost as fast as LCGs (according to my comparison they are only 30% slower than simply inline LCG), having much better quality than LCG the same time.

You can find their code and comparison here: http://xorshift.di.unimi.it/

Falsework

underappreciated answer here - I've used these in a couple projects so far and they work great, with such a simple implementation! – Rosannarosanne