1INITSTATE(3P) POSIX Programmer's Manual INITSTATE(3P)
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6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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13 initstate, random, setstate, srandom — pseudo-random number functions
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16 #include <stdlib.h>
17 char *initstate(unsigned seed, char *state, size_t size);
19 long random(void);
20 char *setstate(char *state);
21 void srandom(unsigned seed);
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24 The random() function shall use a non-linear additive feedback random-
25 number generator employing a default state array size of 31 long inte‐
26 gers to return successive pseudo-random numbers in the range from 0 to
27 231−1. The period of this random-number generator is approximately 16 x
28 (231−1). The size of the state array determines the period of the ran‐
29 dom-number generator. Increasing the state array size shall increase
30 the period.
31 With 256 bytes of state information, the period of the random-number
33 generator shall be greater than 269.
34 Like rand(), random() shall produce by default a sequence of numbers
36 that can be duplicated by calling srandom() with 1 as the seed.
37 The srandom() function shall initialize the current state array using
39 the value of seed.
40 The initstate() and setstate() functions handle restarting and changing
42 random-number generators. The initstate() function allows a state
43 array, pointed to by the state argument, to be initialized for future
44 use. The size argument, which specifies the size in bytes of the state
45 array, shall be used by initstate() to decide what type of random-num‐
46 ber generator to use; the larger the state array, the more random the
47 numbers. Values for the amount of state information are 8, 32, 64, 128,
48 and 256 bytes. Other values greater than 8 bytes are rounded down to
49 the nearest one of these values. If initstate() is called with
50 8≤size<32, then random() shall use a simple linear congruential random
51 number generator. The seed argument specifies a starting point for the
52 random-number sequence and provides for restarting at the same point.
53 The initstate() function shall return a pointer to the previous state
54 information array.
55 If initstate() has not been called, then random() shall behave as
57 though initstate() had been called with seed=1 and size=128.
58 Once a state has been initialized, setstate() allows switching between
60 state arrays. The array defined by the state argument shall be used for
61 further random-number generation until initstate() is called or set‐
62 state() is called again. The setstate() function shall return a pointer
63 to the previous state array.
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66 If initstate() is called with size less than 8, it shall return NULL.
67 The random() function shall return the generated pseudo-random number.
69 The srandom() function shall not return a value.
71 Upon successful completion, initstate() and setstate() shall return a
73 pointer to the previous state array; otherwise, a null pointer shall be
74 returned.
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77 No errors are defined.
78 The following sections are informative.
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82 None.
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85 After initialization, a state array can be restarted at a different
86 point in one of two ways:
87 1. The initstate() function can be used, with the desired seed, state
89 array, and size of the array.
90 2. The setstate() function, with the desired state, can be used, fol‐
92 lowed by srandom() with the desired seed. The advantage of using
93 both of these functions is that the size of the state array does
94 not have to be saved once it is initialized.
95 Although some implementations of random() have written messages to
97 standard error, such implementations do not conform to POSIX.1‐2008.
98 Issue 5 restored the historical behavior of this function.
100 Threaded applications should use erand48(), nrand48(), or jrand48()
102 instead of random() when an independent random number sequence in mul‐
103 tiple threads is required.
104
106 None.
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109 None.
110
112 drand48(), rand()
113 The Base Definitions volume of POSIX.1‐2008, <stdlib.h>
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117 Portions of this text are reprinted and reproduced in electronic form
118 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
119 -- Portable Operating System Interface (POSIX), The Open Group Base
120 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
121 cal and Electronics Engineers, Inc and The Open Group. (This is
122 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
123 event of any discrepancy between this version and the original IEEE and
124 The Open Group Standard, the original IEEE and The Open Group Standard
125 is the referee document. The original Standard can be obtained online
126 at http://www.unix.org/online.html .
127 Any typographical or formatting errors that appear in this page are
129 most likely to have been introduced during the conversion of the source
130 files to man page format. To report such errors, see https://www.ker‐
131 nel.org/doc/man-pages/reporting_bugs.html .
132IEEE/The Open Group 2013 INITSTATE(3P)