1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
|
.\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $OpenBSD: rand.3,v 1.18 2014/12/08 21:45:20 deraadt Exp $
.\"
.Dd $Mdocdate: December 8 2014 $
.Dt RAND 3
.Os
.Sh NAME
.Nm rand ,
.Nm rand_r ,
.Nm srand ,
.Nm srand_deterministic
.Nd bad pseudo-random number generator
.Sh SYNOPSIS
.In stdlib.h
.Ft void
.Fn srand "unsigned int seed"
.Ft void
.Fn srand_deterministic "unsigned int seed"
.Ft int
.Fn rand void
.Ft int
.Fn rand_r "unsigned int *seed"
.Sh DESCRIPTION
.Bf -symbolic
Standards insist that this interface return deterministic results.
Unsafe usage is very common, so
.Ox
changed the subsystem to return non-deterministic results by default.
.Ef
.Pp
To satisfy portable code,
.Fn srand
may be called to initialize the subsystem.
In
.Ox
the
.Ar seed
variable is ignored, and strong random number results will be provided from
.Xr arc4random 3.
In other systems, the
.Ar seed
variable primes a simplistic deterministic algorithm.
.Pp
If the standardized behavior is required
.Fn srand_deterministic
can be substituted for
.Fn srand ,
then subsequent
.Fn rand
calls will return results using the deterministic algorithm.
.Pp
The
.Fn rand
function returns a result in the range of 0 to
.Dv RAND_MAX .
By default, this result comes from
.Xr arc4random 3 .
If
.Fn srand_deterministic
was called, the result will be computed using the deterministic algorithm.
.Pp
The
.Fn rand_r
is a thread-safe version of
.Fn rand .
Storage for the seed must be provided through the
.Fa seed
argument, and needs to have been initialized by the caller.
It always operates using the deterministic algorithm.
.Sh SEE ALSO
.Xr arc4random 3 ,
.Xr rand48 3 ,
.Xr random 3
.Sh STANDARDS
The
.Fn rand
function conforms to
.St -ansiC .
.Pp
The
.Fn rand_r
function conforms to
.St -p1003.1-2008 .
.Pp
The
.Fn srand
function does not conform to
.St -ansiC ,
intentionally.
.Pp
The
.Fn srand_deterministic
function is an OpenBSD extension.
.Sh HISTORY
The functions
.Fn rand
and
.Fn srand
first appeared in
.At v3 .
|
