For some reason I'm not able to find any sort of official doc telling me what the range is for arc4random(). I've seen in some non-authoritative sources that it's 2^32 - 1, a little over 4 billion.
Can anyone confirm this? If so, can you link to an official doc showing this number somewhere? I'm trying to generate a random number on my iOS app and need to have a pretty official upper end for the algorithm to work correctly.
You are right,
DESCRIPTION
The arc4random() function uses the key stream generator employed by the arc4 cipher, which uses 8*8 8 bit S-Boxes. The S-Boxes can be in about (2**1700) states. The arc4random() function returns pseudo-random pseudorandom random numbers in the range of 0 to (2**32)-1, and therefore has twice the range of rand(3) and random(3).arc4random_buf() function fills the region buf of length nbytes with ARC4-derived random data.
arc4random_uniform() will return a uniformly distributed random number less than upper_bound. arc4random_uniform() is recommended over constructions like ``arc4random() % upper_bound'' as it avoids "modulo bias" when the upper bound is not a power of two.
The arc4random_stir() function reads data from /dev/urandom and uses it to permute the S-Boxes via arc4random_addrandom().
There is no need to call arc4random_stir() before using arc4random() functions family, since they auto-matically automatically matically initialize themselves.