The arc4 random number generator.

#include <stdlib.h>

    uint32_t
    arc4random(void);

    void
    arc4random_buf(void *buf, size_t nbytes);

    uint32_t
    arc4random_uniform(uint32_t upper_bound);

    void
    arc4random_stir(void);

    void
    arc4random_addrandom(unsigned char    *dat, int datlen);

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 numbers in the range of 0 to (2**32)-1, and therefore has twice the range of rand.

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 available sources of "Operating System entropy" 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 automatically initialize themselves.

Example

The following produces a drop-in replacement for the traditional rand() and random() functions using arc4random():
      #define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1))

Requirements