ARC4RANDOM(3C) Standard C Library Functions ARC4RANDOM(3C)

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

This family of functions provides higher quality data than those described
in rand(3C), random(3C), and rand48(3C).

Use of these functions is encouraged for almost all random number
consumption because the other interfaces are deficient in either quality,
portability, standardization, or availability. These functions can be
called in almost all coding environments, including pthreads(7) and
chroot(2).

High quality 32-bit pseudo-random numbers are generated very quickly. On
each call, a cryptographic pseudo-random number generator is used to
generate a new result. 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 using getentropy(3C) on a regular basis, and also upon fork(2).

The arc4random() function 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
constructions 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 consume multiple iterations to ensure uniformity; see the
source code to understand the problem and solution.

RETURN VALUES

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

INTERFACE STABILITY

Committed

MT-LEVEL
MT-Safe

SEE ALSO

rand(3C), rand48(3C), random(3C)

illumos December 31, 2014 illumos