1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
|
<head>
<title>rand(3) - Plan 9 from User Space</title>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
</head>
<body bgcolor=#ffffff>
<table border=0 cellpadding=0 cellspacing=0 width=100%>
<tr height=10><td>
<tr><td width=20><td>
<tr><td width=20><td><b>RAND(3)</b><td align=right><b>RAND(3)</b>
<tr><td width=20><td colspan=2>
<br>
<p><font size=+1><b>NAME </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand,
fastrand, nfastrand – random number generator<br>
</table>
<p><font size=+1><b>SYNOPSIS </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>#include <u.h><br>
#include <libc.h>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int rand(void)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>long lrand(void)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>double frand(void)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>int nrand(int val)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>long lnrand(long val)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>void srand(long seed)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>ulong truerand(void)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>ulong ntruerand(ulong val)<br>
#include <mp.h><br>
#include <libsec.h>
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>void genrandom(uchar *buf, int nbytes)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>void prng(uchar *buf, int nbytes)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>ulong fastrand(void)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
<tt><font size=+1>ulong nfastrand(ulong val)<br>
</font></tt>
</table>
<p><font size=+1><b>DESCRIPTION </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<i>Rand</i> returns a uniform pseudo-random number <i>x</i>, 0≤<i>x</i><215.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Lrand</i> returns a uniform <tt><font size=+1>long</font></tt> <i>x</i>, 0≤<i>x</i><231.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Frand</i> returns a uniform <tt><font size=+1>double</font></tt> <i>x</i>, 0.0≤<i>x</i><1.0, This function calls
<i>lrand</i> twice to generate a number with as many as 62 significant
bits of mantissa.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Nrand</i> returns a uniform integer <i>x</i>, 0≤<i>x</i><<i>val. Lnrand</i> is the same,
but returns a <tt><font size=+1>long</font></tt>.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
The algorithm is additive feedback with:<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
x[n] = (x[n-273] + x[n-607]) mod 231
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</table>
giving a period of 230 × (2607 – 1).
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
The generators are initialized by calling <i>srand</i> with whatever
you like as argument. To get a different starting value each time,<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>srand(time(0))
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
</table>
will work as long as it is not called more often than once per
second. Calling<br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>srand(1)
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</font></tt>
</table>
will initialize the generators to their starting state.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Truerand</i> returns a random unsigned long read from <tt><font size=+1>/dev/random</font></tt>.
Due to the nature of <tt><font size=+1>/dev/random</font></tt>, truerand can only return a few
hundred bits a second.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Ntruerand</i> returns a uniform random integer <i>x</i>, 0≤<i>x</i><<i>val</i>≤<i>232-1.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</i>
<i>Genrandom</i> fills a buffer with bytes from the X9.17 pseudo-random
number generator. The X9.17 generator is seeded by 24 truly random
bytes read from <tt><font size=+1>/dev/random</font></tt>.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Prng</i> uses the native <a href="../man3/rand.html"><i>rand</i>(3)</a> pseudo-random number generator to
fill the buffer. Used with <i>srand</i>, this function can produce a
reproducible stream of pseudo random numbers useful in testing.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
Both <i>genrandom</i> and <i>prng</i> may be passed to <i>mprand</i> (see <a href="../man3/mp.html"><i>mp</i>(3)</a>).
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
<i>Fastrand</i> uses <i>genrandom</i> to return a uniform <tt><font size=+1>unsigned long</font></tt> <i>x</i>, 0≤<i>x</i><<i>232-1.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
</i>
<i>Nfastrand</i> uses <i>genrandom</i> to return a uniform <tt><font size=+1>unsigned long</font></tt> <i>x</i>,
0≤<i>x</i><<i>val</i>≤<i>232-1.<br>
</i>
</table>
<p><font size=+1><b>SOURCE </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<tt><font size=+1>/usr/local/plan9/src/lib9<br>
/usr/local/plan9/src/libsec/port<br>
</font></tt>
</table>
<p><font size=+1><b>SEE ALSO </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<a href="../man3/mp.html"><i>mp</i>(3)</a><br>
</table>
<p><font size=+1><b>BUGS </b></font><br>
<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
<i>Truerand</i> and <i>ntruerand</i> maintain a static file descriptor.
<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
To avoid name conflicts with the underlying system, <i>rand</i>, <i>lrand</i>,
<i>frand</i>, <i>nrand</i>, <i>lnrand</i>, and <i>srand</i> are preprocessor macros defined
as <i>p9rand</i>, <i>p9lrand</i>, and so on; see <a href="../man3/intro.html"><i>intro</i>(3)</a>.<br>
</table>
<td width=20>
<tr height=20><td>
</table>
<!-- TRAILER -->
<table border=0 cellpadding=0 cellspacing=0 width=100%>
<tr height=15><td width=10><td><td width=10>
<tr><td><td>
<center>
<a href="../../"><img src="../../dist/spaceglenda100.png" alt="Space Glenda" border=1></a>
</center>
</table>
<!-- TRAILER -->
</body></html>
|