ARC4RANDOM(3)						   BSD Library Functions Manual 					     ARC4RANDOM(3)

NAME

     arc4random, arc4random_buf, arc4random_uniform -- random number generator

SYNOPSIS

     #include <stdlib.h>

     uint32_t
     arc4random(void);

     void
     arc4random_buf(void *buf, size_t nbytes);

     uint32_t
     arc4random_uniform(uint32_t upper_bound);

DESCRIPTION

     These functions use a cryptographic pseudo-random number generator to generate high quality random bytes very quickly.  One data pool is used
     for all consumers in a process, so that consumption under program flow can act as additional stirring.  The subsystem is re-seeded from the
     kernel random number subsystem on a regular basis, and also upon fork(2).

     This family of functions provides higher quality random data than those described in rand(3), random(3), and rand48(3).  They can be called
     in almost all environments, including chroot(2), and their use is encouraged over all other standard library functions for random numbers.

     arc4random() returns a single 32-bit value.

     arc4random_buf() fills the region buf of length nbytes with random data.

     arc4random_uniform() will return a single 32-bit value, uniformly distributed but less than upper_bound.  This is recommended over construc-
     tions like ``arc4random() % upper_bound'' as it avoids "modulo bias" when the upper bound is not a power of two.  In the worst case, this
     function may require multiple iterations to ensure uniformity.

RETURN VALUES

     These functions are always successful, and no return value is reserved to indicate an error.

SEE ALSO

     rand(3), rand48(3), random(3), random(4)

HISTORY

     The original version of this random number generator used the RC4 (also known as ARC4) algorithm.	In OS X 10.12 it was replaced with the
     NIST-approved AES cipher, and it may be replaced again in the future as cryptographic techniques advance.	A good mnemonic is ``A Replacement
     Call for Random''.

BSD
								   July 30, 2015							       BSD