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.\"     @(#)rand.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd April 2, 2013
.Dt RAND 3
.Os
.Sh NAME
.Nm rand ,
.Nm srand ,
.Nm sranddev ,
.Nm rand_r
.Nd bad random number generator
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft void
.Fn srand "unsigned seed"
.Ft void
.Fn sranddev void
.Ft int
.Fn rand void
.Ft int
.Fn rand_r "unsigned *ctx"
.Sh DESCRIPTION
.Bf -symbolic
The functions described in this manual page are not cryptographically
secure.
Cryptographic applications should use
.Xr arc4random 3
instead.
.Ef
.Pp
These interfaces are obsoleted by
.Xr random 3 .
.Pp
The
.Fn rand
function computes a sequence of pseudo-random integers in the range
of 0 to
.Dv RAND_MAX
(as defined by the header file
.In stdlib.h ) .
.Pp
The
.Fn srand
function sets its argument
.Fa seed
as the seed for a new sequence of
pseudo-random numbers to be returned by
.Fn rand .
These sequences are repeatable by calling
.Fn srand
with the same seed value.
.Pp
If no
.Fa seed
value is provided, the functions are automatically
seeded with a value of 1.
.Pp
The
.Fn sranddev
function initializes a seed using pseudo-random numbers obtained from the kernel.
.Pp
The
.Fn rand_r
function
provides the same functionality as
.Fn rand .
A pointer to the context value
.Fa ctx
must be supplied by the caller.
.Pp
For better generator quality, use
.Xr random 3
or
.Xr lrand48 3 .
.Sh SEE ALSO
.Xr arc4random 3 ,
.Xr lrand48 3 ,
.Xr random 3 ,
.Xr random 4
.Sh STANDARDS
The
.Fn rand
and
.Fn srand
functions
conform to
.St -isoC .
.Pp
The
.Fn rand_r
function is as proposed in the POSIX.4a Draft #6 document.