1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" Permission is granted to make and distribute verbatim copies of this
4 .\" manual provided the copyright notice and this permission notice are
5 .\" preserved on all copies.
7 .\" Permission is granted to copy and distribute modified versions of this
8 .\" manual under the conditions for verbatim copying, provided that the
9 .\" entire resulting derived work is distributed under the terms of a
10 .\" permission notice identical to this one.
12 .\" Since the Linux kernel and libraries are constantly changing, this
13 .\" manual page may be incorrect or out-of-date. The author(s) assume no
14 .\" responsibility for errors or omissions, or for damages resulting from
15 .\" the use of the information contained herein. The author(s) may not
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17 .\" which is licensed free of charge, as they might when working
20 .\" Formatted or processed versions of this manual, if unaccompanied by
21 .\" the source, must acknowledge the copyright and authors of this work.
23 .\" References consulted:
24 .\" Linux libc source code
25 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
27 .\" Modified Sun Mar 28 00:25:51 1993, David Metcalfe
28 .\" Modified Sat Jul 24 18:13:39 1993 by Rik Faith (faith@cs.unc.edu)
29 .\" Modified Sun Aug 20 21:47:07 2000, aeb
31 .TH RANDOM 3 2009-02-03 "GNU" "Linux Programmer's Manual"
33 random, srandom, initstate, setstate \- random number generator
36 .B #include <stdlib.h>
38 .B long int random(void);
40 .BI "void srandom(unsigned int " seed );
42 .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)):
57 _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
62 function uses a nonlinear additive feedback random
63 number generator employing a default table of size 31 long integers to
64 return successive pseudo-random numbers in
65 the range from 0 to \fBRAND_MAX\fR.
66 The period of this random number generator is very large, approximately
67 .IR "16\ *\ ((2^31)\ \-\ 1)" .
71 function sets its argument as the seed for a new
72 sequence of pseudo-random integers to be returned by
74 These sequences are repeatable by calling
78 If no seed value is provided, the
81 is automatically seeded with a value of 1.
85 function allows a state array \fIstate\fP to
86 be initialized for use by
88 The size of the state array
91 to decide how sophisticated a
92 random number generator it should use \(em the larger the state array,
93 the better the random numbers will be.
94 \fIseed\fP is the seed for the
95 initialization, which specifies a starting point for the random number
96 sequence, and provides for restarting at the same point.
100 function changes the state array used by the
103 The state array \fIstate\fP is used for
104 random number generation until the next call to
108 \fIstate\fP must first have been initialized
111 or be the result of a previous call of
116 function returns a value between 0 and
120 function returns no value.
125 functions return a pointer to the previous state
126 array, or NULL on error.
130 A state array of less than 8 bytes was specified to
133 4.3BSD, POSIX.1-2001.
135 Current "optimal" values for the size of the state array \fIn\fP are
136 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
137 the nearest known amount.
138 Using less than 8 bytes will cause an
141 This function should not be used in cases where multiple threads use
143 and the behavior should be reproducible.
148 Random-number generation is a complex topic.
149 .I Numerical Recipes in C: The Art of Scientific Computing
150 (William H. Press, Brian P. Flannery, Saul A. Teukolsky, William
151 T. Vetterling; New York: Cambridge University Press, 2007, 3rd ed.)
152 provides an excellent discussion of practical random-number generation
153 issues in Chapter 7 (Random Numbers).
155 For a more theoretical discussion which also covers many practical issues
156 in depth, see Chapter 3 (Random Numbers) in Donald E. Knuth's
157 .IR "The Art of Computer Programming" ,
158 volume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts:
159 Addison-Wesley Publishing Company, 1981.