1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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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 2015-02-01 "GNU" "Linux Programmer's Manual"
35 random, srandom, initstate, setstate \- random number generator
38 .B #include <stdlib.h>
40 .B long int random(void);
42 .BI "void srandom(unsigned int " seed );
44 .BI "char *initstate(unsigned int " seed ", char *" state ", size_t " n );
46 .BI "char *setstate(char *" state );
50 Feature Test Macro Requirements for glibc (see
51 .BR feature_test_macros (7)):
60 _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
61 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
67 function uses a nonlinear additive feedback random
68 number generator employing a default table of size 31 long integers to
69 return successive pseudo-random numbers in
70 the range from 0 to \fBRAND_MAX\fR.
71 The period of this random number generator is very large, approximately
72 .IR "16\ *\ ((2^31)\ \-\ 1)" .
76 function sets its argument as the seed for a new
77 sequence of pseudo-random integers to be returned by
79 These sequences are repeatable by calling
83 If no seed value is provided, the
86 is automatically seeded with a value of 1.
90 function allows a state array \fIstate\fP to
91 be initialized for use by
93 The size of the state array
96 to decide how sophisticated a
97 random number generator it should use\(emthe larger the state array,
98 the better the random numbers will be.
99 \fIseed\fP is the seed for the
100 initialization, which specifies a starting point for the random number
101 sequence, and provides for restarting at the same point.
105 function changes the state array used by the
108 The state array \fIstate\fP is used for
109 random number generation until the next call to
113 \fIstate\fP must first have been initialized
116 or be the result of a previous call of
121 function returns a value between 0 and
125 function returns no value.
129 function returns a pointer to the previous state array.
132 is set to indicate the cause.
136 returns a pointer to the previous state array.
137 On error, it returns NULL, with
139 set to indicate the cause of the error.
150 A state array of less than 8 bytes was specified to
153 .SS Multithreading (see pthreads(7))
160 functions are thread-safe.
162 4.3BSD, POSIX.1-2001.
164 Current "optimal" values for the size of the state array \fIn\fP are
165 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
166 the nearest known amount.
167 Using less than 8 bytes will cause an
170 This function should not be used in cases where multiple threads use
172 and the behavior should be reproducible.
177 Random-number generation is a complex topic.
178 .I Numerical Recipes in C: The Art of Scientific Computing
179 (William H. Press, Brian P. Flannery, Saul A. Teukolsky, William
180 T. Vetterling; New York: Cambridge University Press, 2007, 3rd ed.)
181 provides an excellent discussion of practical random-number generation
182 issues in Chapter 7 (Random Numbers).
184 For a more theoretical discussion which also covers many practical issues
185 in depth, see Chapter 3 (Random Numbers) in Donald E. Knuth's
186 .IR "The Art of Computer Programming" ,
187 volume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts:
188 Addison-Wesley Publishing Company, 1981.
192 should return NULL on error.
193 In the glibc implementation,
195 is (as specified) set on error, but the function does not return NULL.
196 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=15380
204 This page is part of release 3.79 of the Linux
207 A description of the project,
208 information about reporting bugs,
209 and the latest version of this page,
211 \%http://www.kernel.org/doc/man\-pages/.