xref: /freebsd/lib/libc/stdlib/rand.3 (revision f4b37ed0f8b307b1f3f0f630ca725d68f1dff30d)
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32.\"     @(#)rand.3	8.1 (Berkeley) 6/4/93
33.\" $FreeBSD$
34.\"
35.Dd April 2, 2013
36.Dt RAND 3
37.Os
38.Sh NAME
39.Nm rand ,
40.Nm srand ,
41.Nm sranddev ,
42.Nm rand_r
43.Nd bad random number generator
44.Sh LIBRARY
45.Lb libc
46.Sh SYNOPSIS
47.In stdlib.h
48.Ft void
49.Fn srand "unsigned seed"
50.Ft void
51.Fn sranddev void
52.Ft int
53.Fn rand void
54.Ft int
55.Fn rand_r "unsigned *ctx"
56.Sh DESCRIPTION
57.Bf -symbolic
58The functions described in this manual page are not cryptographically
59secure.
60Cryptographic applications should use
61.Xr arc4random 3
62instead.
63.Ef
64.Pp
65These interfaces are obsoleted by
66.Xr random 3 .
67.Pp
68The
69.Fn rand
70function computes a sequence of pseudo-random integers in the range
71of 0 to
72.Dv RAND_MAX
73(as defined by the header file
74.In stdlib.h ) .
75.Pp
76The
77.Fn srand
78function sets its argument
79.Fa seed
80as the seed for a new sequence of
81pseudo-random numbers to be returned by
82.Fn rand .
83These sequences are repeatable by calling
84.Fn srand
85with the same seed value.
86.Pp
87If no
88.Fa seed
89value is provided, the functions are automatically
90seeded with a value of 1.
91.Pp
92The
93.Fn sranddev
94function initializes a seed using pseudo-random numbers obtained from the kernel.
95.Pp
96The
97.Fn rand_r
98function
99provides the same functionality as
100.Fn rand .
101A pointer to the context value
102.Fa ctx
103must be supplied by the caller.
104.Pp
105For better generator quality, use
106.Xr random 3
107or
108.Xr lrand48 3 .
109.Sh SEE ALSO
110.Xr arc4random 3 ,
111.Xr lrand48 3 ,
112.Xr random 3 ,
113.Xr random 4
114.Sh STANDARDS
115The
116.Fn rand
117and
118.Fn srand
119functions
120conform to
121.St -isoC .
122.Pp
123The
124.Fn rand_r
125function is as proposed in the POSIX.4a Draft #6 document.
126