1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .\" References consulted:
26 .\" Linux libc source code
27 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
29 .\" Modified Sun Mar 28 00:25:51 1993, David Metcalfe
30 .\" Modified Sat Jul 24 18:13:39 1993 by Rik Faith (faith@cs.unc.edu)
31 .\" Modified Sun Aug 20 21:47:07 2000, aeb
33 .TH RANDOM 3 2021-03-22 "GNU" "Linux Programmer's Manual"
35 random, srandom, initstate, setstate \- random number generator
38 .B #include <stdlib.h>
41 .BI "void srandom(unsigned int " seed );
43 .BI "char *initstate(unsigned int " seed ", char *" state ", size_t " n );
44 .BI "char *setstate(char *" state );
48 Feature Test Macro Requirements for glibc (see
49 .BR feature_test_macros (7)):
58 .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
59 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
60 || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
65 function uses a nonlinear additive feedback random
66 number generator employing a default table of size 31 long integers to
67 return successive pseudo-random numbers in
68 the range from 0 to 2^31\ \-\ 1.
69 The period of this random number generator is very large, approximately
70 .IR "16\ *\ ((2^31)\ \-\ 1)" .
74 function sets its argument as the seed for a new
75 sequence of pseudo-random integers to be returned by
77 These sequences are repeatable by calling
81 If no seed value is provided, the
84 is automatically seeded with a value of 1.
88 function allows a state array \fIstate\fP to
89 be initialized for use by
91 The size of the state array
94 to decide how sophisticated a
95 random number generator it should use\(emthe larger the state array,
96 the better the random numbers will be.
97 Current "optimal" values for the size of the state array \fIn\fP are
98 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
99 the nearest known amount.
100 Using less than 8 bytes results in an error.
101 \fIseed\fP is the seed for the
102 initialization, which specifies a starting point for the random number
103 sequence, and provides for restarting at the same point.
107 function changes the state array used by the
110 The state array \fIstate\fP is used for
111 random number generation until the next call to
115 \fIstate\fP must first have been initialized
118 or be the result of a previous call of
123 function returns a value between 0 and
124 .IR "(2^31)\ \-\ 1" .
127 function returns no value.
131 function returns a pointer to the previous state array.
132 On failure, it returns NULL, and
134 is set to indicate the error.
138 returns a pointer to the previous state array.
139 On failure, it returns NULL, and
141 is set to indicate the error.
152 A state array of less than 8 bytes was specified to
155 For an explanation of the terms used in this section, see
163 Interface Attribute Value
169 T} Thread safety MT-Safe
175 POSIX.1-2001, POSIX.1-2008, 4.3BSD.
179 function should not be used in multithreaded programs
180 where reproducible behavior is required.
185 Random-number generation is a complex topic.
186 .I Numerical Recipes in C: The Art of Scientific Computing
187 (William H.\& Press, Brian P.\& Flannery, Saul A.\& Teukolsky,
188 William T.\& Vetterling; New York: Cambridge University Press, 2007, 3rd ed.)
189 provides an excellent discussion of practical random-number generation
190 issues in Chapter 7 (Random Numbers).
192 For a more theoretical discussion which also covers many practical issues
193 in depth, see Chapter 3 (Random Numbers) in Donald E.\& Knuth's
194 .IR "The Art of Computer Programming" ,
195 volume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts:
196 Addison-Wesley Publishing Company, 1981.
200 should return NULL on error.
201 In the glibc implementation,
203 is (as specified) set on error, but the function does not return NULL.
204 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=15380