Arc4random random number generator

Question

int randomNumber = (arc4random() % 83) + 1; 

Is this the best way to generate the most random number? Or is there a better way to generate a random number?

Answer 1

arc4random has an excellent algorithm for generating random numbers based on the current time. There are other functions of rand, but they are not so good and require seeding.

Answer 2

When you use arc4random , you avoid one mistake when using % with linear congruent generators (which is the usual algorithm used by rand ): the least significant bits are no less random.

However, you still have truncation problems: i.e. because (1 << 32) % 83 is 77, which means that numbers from 0 to 76 appear (slightly) more often than numbers between 77 and 82. To avoid this, you must throw away the input value (that is, call arc4random again) if it is higher (1 << 32) / 83 * 83 .

(I assume that arc4random range from 0 to 2 ³² -1. Edit the explanation above accordingly.)

Answer 3

The best random number generator I've ever seen (as well as a very clear definition of what random means) can be found in Stephen Wolfram's “A New Kind of Science”. He used very simple cellular automata as his random number generator for decades in his Mathematica program, so he was very well tested.