190 lines
8.1 KiB
HTML
190 lines
8.1 KiB
HTML
<head>
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<title>rand(3) - Plan 9 from User Space</title>
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<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
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</head>
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<body bgcolor=#ffffff>
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<table border=0 cellpadding=0 cellspacing=0 width=100%>
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<tr height=10><td>
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<tr><td width=20><td>
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<tr><td width=20><td><b>RAND(3)</b><td align=right><b>RAND(3)</b>
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<tr><td width=20><td colspan=2>
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<br>
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<p><font size=+1><b>NAME </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand,
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fastrand, nfastrand – random number generator<br>
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</table>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>#include <u.h><br>
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#include <libc.h>
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>int rand(void)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>long lrand(void)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>double frand(void)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>int nrand(int val)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>long lnrand(long val)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>void srand(long seed)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>ulong truerand(void)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>ulong ntruerand(ulong val)<br>
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#include <mp.h><br>
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#include <libsec.h>
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>void genrandom(uchar *buf, int nbytes)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>void prng(uchar *buf, int nbytes)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>ulong fastrand(void)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>ulong nfastrand(ulong val)<br>
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</font></tt>
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</table>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<i>Rand</i> returns a uniform pseudo-random number <i>x</i>, 0≤<i>x</i><215.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Lrand</i> returns a uniform <tt><font size=+1>long</font></tt> <i>x</i>, 0≤<i>x</i><231.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<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
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<i>lrand</i> twice to generate a number with as many as 62 significant
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bits of mantissa.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Nrand</i> returns a uniform integer <i>x</i>, 0≤<i>x</i><<i>val. Lnrand</i> is the same,
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but returns a <tt><font size=+1>long</font></tt>.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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The algorithm is additive feedback with:<br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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x[n] = (x[n-273] + x[n-607]) mod 231
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</table>
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giving a period of 230 × (2607 – 1).
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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The generators are initialized by calling <i>srand</i> with whatever
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you like as argument. To get a different starting value each time,<br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>srand(time(0))
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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</table>
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will work as long as it is not called more often than once per
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second. Calling<br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>srand(1)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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</table>
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will initialize the generators to their starting state.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Truerand</i> returns a random unsigned long read from <tt><font size=+1>/dev/random</font></tt>.
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Due to the nature of <tt><font size=+1>/dev/random</font></tt>, truerand can only return a few
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hundred bits a second.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Ntruerand</i> returns a uniform random integer <i>x</i>, 0≤<i>x</i><<i>val</i>≤<i>232-1.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</i>
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<i>Genrandom</i> fills a buffer with bytes from the X9.17 pseudo-random
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number generator. The X9.17 generator is seeded by 24 truly random
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bytes read from <tt><font size=+1>/dev/random</font></tt>.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Prng</i> uses the native <a href="../man3/rand.html"><i>rand</i>(3)</a> pseudo-random number generator to
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fill the buffer. Used with <i>srand</i>, this function can produce a
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reproducible stream of pseudo random numbers useful in testing.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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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>).
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<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.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</i>
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<i>Nfastrand</i> uses <i>genrandom</i> to return a uniform <tt><font size=+1>unsigned long</font></tt> <i>x</i>,
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0≤<i>x</i><<i>val</i>≤<i>232-1.<br>
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</i>
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</table>
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<p><font size=+1><b>SOURCE </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>/usr/local/plan9/src/lib9<br>
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/usr/local/plan9/src/libsec/port<br>
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</font></tt>
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</table>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<a href="../man3/mp.html"><i>mp</i>(3)</a><br>
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</table>
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<p><font size=+1><b>BUGS </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<i>Truerand</i> and <i>ntruerand</i> maintain a static file descriptor.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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To avoid name conflicts with the underlying system, <i>rand</i>, <i>lrand</i>,
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<i>frand</i>, <i>nrand</i>, <i>lnrand</i>, and <i>srand</i> are preprocessor macros defined
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as <i>p9rand</i>, <i>p9lrand</i>, and so on; see <a href="../man3/intro.html"><i>intro</i>(3)</a>.<br>
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</table>
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<td width=20>
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<tr height=20><td>
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</table>
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<!-- TRAILER -->
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<table border=0 cellpadding=0 cellspacing=0 width=100%>
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<tr height=15><td width=10><td><td width=10>
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<tr><td><td>
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<center>
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<a href="../../"><img src="../../dist/spaceglenda100.png" alt="Space Glenda" border=1></a>
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</center>
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</table>
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<!-- TRAILER -->
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</body></html>
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