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1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
2 | .\" | |
93015253 | 3 | .\" %%%LICENSE_START(VERBATIM) |
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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. | |
7 | .\" | |
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. | |
c13182ef | 12 | .\" |
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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14 | .\" manual page may be incorrect or out-of-date.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 | |
19 | .\" professionally. | |
c13182ef | 20 | .\" |
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21 | .\" Formatted or processed versions of this manual, if unaccompanied by |
22 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 23 | .\" %%%LICENSE_END |
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24 | .\" |
25 | .\" References consulted: | |
26 | .\" Linux libc source code | |
27 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
28 | .\" 386BSD man pages | |
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 | |
32 | .\" | |
97986708 | 33 | .TH RANDOM 3 2016-03-15 "GNU" "Linux Programmer's Manual" |
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34 | .SH NAME |
35 | random, srandom, initstate, setstate \- random number generator | |
36 | .SH SYNOPSIS | |
37 | .nf | |
38 | .B #include <stdlib.h> | |
39 | .sp | |
40 | .B long int random(void); | |
5895e7eb | 41 | |
fea681da | 42 | .BI "void srandom(unsigned int " seed ); |
5895e7eb | 43 | |
fea681da | 44 | .BI "char *initstate(unsigned int " seed ", char *" state ", size_t " n ); |
defcceb3 | 45 | .br |
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46 | .BI "char *setstate(char *" state ); |
47 | .fi | |
cc4615cc MK |
48 | .sp |
49 | .in -4n | |
50 | Feature Test Macro Requirements for glibc (see | |
51 | .BR feature_test_macros (7)): | |
52 | .in | |
53 | .sp | |
54 | .ad l | |
55 | .BR random (), | |
56 | .BR srandom (), | |
57 | .BR initstate (), | |
58 | .BR setstate (): | |
bb1029be | 59 | .RS 4 |
2b1b0424 | 60 | _XOPEN_SOURCE\ >=\ 500 |
cf7fa0a1 | 61 | .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED |
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62 | || /* Glibc since 2.19: */ _DEFAULT_SOURCE |
63 | || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE | |
bb1029be MK |
64 | .RE |
65 | .ad | |
fea681da | 66 | .SH DESCRIPTION |
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67 | The |
68 | .BR random () | |
fb0e9c48 | 69 | function uses a nonlinear additive feedback random |
fea681da | 70 | number generator employing a default table of size 31 long integers to |
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71 | return successive pseudo-random numbers in |
72 | the range from 0 to \fBRAND_MAX\fR. | |
fea681da | 73 | The period of this random number generator is very large, approximately |
b983ad10 | 74 | .IR "16\ *\ ((2^31)\ \-\ 1)" . |
fea681da | 75 | .PP |
60a90ecd MK |
76 | The |
77 | .BR srandom () | |
78 | function sets its argument as the seed for a new | |
79 | sequence of pseudo-random integers to be returned by | |
80 | .BR random (). | |
81 | These sequences are repeatable by calling | |
82 | .BR srandom () | |
83 | with the same | |
c13182ef | 84 | seed value. |
60a90ecd MK |
85 | If no seed value is provided, the |
86 | .BR random () | |
87 | function | |
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88 | is automatically seeded with a value of 1. |
89 | .PP | |
60a90ecd MK |
90 | The |
91 | .BR initstate () | |
92 | function allows a state array \fIstate\fP to | |
93 | be initialized for use by | |
94 | .BR random (). | |
c13182ef | 95 | The size of the state array |
60a90ecd MK |
96 | \fIn\fP is used by |
97 | .BR initstate () | |
98 | to decide how sophisticated a | |
5503c85e | 99 | random number generator it should use\(emthe larger the state array, |
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100 | the better the random numbers will be. |
101 | \fIseed\fP is the seed for the | |
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102 | initialization, which specifies a starting point for the random number |
103 | sequence, and provides for restarting at the same point. | |
104 | .PP | |
60a90ecd MK |
105 | The |
106 | .BR setstate () | |
107 | function changes the state array used by the | |
108 | .BR random () | |
109 | function. | |
c13182ef | 110 | The state array \fIstate\fP is used for |
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111 | random number generation until the next call to |
112 | .BR initstate () | |
113 | or | |
114 | .BR setstate (). | |
115 | \fIstate\fP must first have been initialized | |
116 | using | |
117 | .BR initstate () | |
118 | or be the result of a previous call of | |
119 | .BR setstate (). | |
47297adb | 120 | .SH RETURN VALUE |
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121 | The |
122 | .BR random () | |
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123 | function returns a value between 0 and |
124 | .BR RAND_MAX . | |
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125 | The |
126 | .BR srandom () | |
127 | function returns no value. | |
6d1a3ba6 | 128 | |
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129 | The |
130 | .BR initstate () | |
247cb8f5 | 131 | function returns a pointer to the previous state array. |
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132 | On error, |
133 | .I errno | |
134 | is set to indicate the cause. | |
135 | ||
136 | On success, | |
60a90ecd | 137 | .BR setstate () |
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138 | returns a pointer to the previous state array. |
139 | On error, it returns NULL, with | |
140 | .I errno | |
141 | set to indicate the cause of the error. | |
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142 | .SH ERRORS |
143 | .TP | |
144 | .B EINVAL | |
d2fdbe9c MK |
145 | The |
146 | .I state | |
147 | argument given to | |
148 | .BR setstate () | |
149 | was NULL. | |
150 | .TP | |
151 | .B EINVAL | |
60a90ecd MK |
152 | A state array of less than 8 bytes was specified to |
153 | .BR initstate (). | |
a04d1466 | 154 | .SH ATTRIBUTES |
52f091ee PH |
155 | For an explanation of the terms used in this section, see |
156 | .BR attributes (7). | |
157 | .TS | |
158 | allbox; | |
159 | lbw23 lb lb | |
160 | l l l. | |
161 | Interface Attribute Value | |
162 | T{ | |
a04d1466 PH |
163 | .BR random (), |
164 | .BR srandom (), | |
52f091ee | 165 | .br |
a04d1466 | 166 | .BR initstate (), |
a04d1466 | 167 | .BR setstate () |
52f091ee PH |
168 | T} Thread safety MT-Safe |
169 | .TE | |
47297adb | 170 | .SH CONFORMING TO |
a87a3e17 | 171 | POSIX.1-2001, POSIX.1-2008, 4.3BSD. |
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172 | .SH NOTES |
173 | Current "optimal" values for the size of the state array \fIn\fP are | |
174 | 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to | |
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175 | the nearest known amount. |
176 | Using less than 8 bytes will cause an | |
fea681da | 177 | error. |
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178 | .PP |
179 | This function should not be used in cases where multiple threads use | |
180 | .BR random () | |
181 | and the behavior should be reproducible. | |
182 | Use | |
183 | .BR random_r (3) | |
184 | for that purpose. | |
185 | .PP | |
186 | Random-number generation is a complex topic. | |
187 | .I Numerical Recipes in C: The Art of Scientific Computing | |
188 | (William H. Press, Brian P. Flannery, Saul A. Teukolsky, William | |
189 | T. Vetterling; New York: Cambridge University Press, 2007, 3rd ed.) | |
190 | provides an excellent discussion of practical random-number generation | |
191 | issues in Chapter 7 (Random Numbers). | |
192 | .PP | |
193 | For a more theoretical discussion which also covers many practical issues | |
194 | in depth, see Chapter 3 (Random Numbers) in Donald E. Knuth's | |
195 | .IR "The Art of Computer Programming" , | |
196 | volume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts: | |
197 | Addison-Wesley Publishing Company, 1981. | |
e6183193 MK |
198 | .SH BUGS |
199 | According to POSIX, | |
200 | .BR initstate () | |
201 | should return NULL on error. | |
202 | In the glibc implementation, | |
203 | .I errno | |
204 | is (as specified) set on error, but the function does not return NULL. | |
205 | .\" http://sourceware.org/bugzilla/show_bug.cgi?id=15380 | |
47297adb | 206 | .SH SEE ALSO |
5b475602 | 207 | .BR drand48 (3), |
d929b801 | 208 | .BR getrandom (2), |
fea681da | 209 | .BR rand (3), |
2d64f60e | 210 | .BR random_r (3), |
fea681da | 211 | .BR srand (3) |