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100 lines
4.8 KiB
HTML
100 lines
4.8 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This manual describes how to install and use the GNU multiple precision
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arithmetic library, version 6.1.0.
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Copyright 1991, 1993-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document under
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the terms of the GNU Free Documentation License, Version 1.3 or any later
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version published by the Free Software Foundation; with no Invariant Sections,
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with the Front-Cover Texts being "A GNU Manual", and with the Back-Cover
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Texts being "You have freedom to copy and modify this GNU Manual, like GNU
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software". A copy of the license is included in
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GNU Free Documentation License. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Random State Seeding (GNU MP 6.1.0)</title>
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<meta name="description" content="How to install and use the GNU multiple precision arithmetic library, version 6.1.0.">
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<meta name="keywords" content="Random State Seeding (GNU MP 6.1.0)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="Random-Number-Functions.html#Random-Number-Functions" rel="up" title="Random Number Functions">
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<link href="Random-State-Miscellaneous.html#Random-State-Miscellaneous" rel="next" title="Random State Miscellaneous">
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<link href="Random-State-Initialization.html#Random-State-Initialization" rel="prev" title="Random State Initialization">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Random-State-Seeding"></a>
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<div class="header">
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<p>
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Next: <a href="Random-State-Miscellaneous.html#Random-State-Miscellaneous" accesskey="n" rel="next">Random State Miscellaneous</a>, Previous: <a href="Random-State-Initialization.html#Random-State-Initialization" accesskey="p" rel="prev">Random State Initialization</a>, Up: <a href="Random-Number-Functions.html#Random-Number-Functions" accesskey="u" rel="up">Random Number Functions</a> [<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Random-State-Seeding-1"></a>
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<h3 class="section">9.2 Random State Seeding</h3>
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<a name="index-Random-number-seeding"></a>
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<a name="index-Seeding-random-numbers"></a>
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<dl>
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<dt><a name="index-gmp_005frandseed"></a>Function: <em>void</em> <strong>gmp_randseed</strong> <em>(gmp_randstate_t <var>state</var>, const mpz_t <var>seed</var>)</em></dt>
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<dt><a name="index-gmp_005frandseed_005fui"></a>Function: <em>void</em> <strong>gmp_randseed_ui</strong> <em>(gmp_randstate_t <var>state</var>, unsigned long int <var>seed</var><!-- /@w -->)</em></dt>
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<dd><p>Set an initial seed value into <var>state</var>.
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</p>
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<p>The size of a seed determines how many different sequences of random numbers
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that it’s possible to generate. The “quality” of the seed is the randomness
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of a given seed compared to the previous seed used, and this affects the
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randomness of separate number sequences. The method for choosing a seed is
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critical if the generated numbers are to be used for important applications,
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such as generating cryptographic keys.
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</p>
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<p>Traditionally the system time has been used to seed, but care needs to be
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taken with this. If an application seeds often and the resolution of the
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system clock is low, then the same sequence of numbers might be repeated.
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Also, the system time is quite easy to guess, so if unpredictability is
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required then it should definitely not be the only source for the seed value.
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On some systems there’s a special device <samp>/dev/random</samp> which provides
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random data better suited for use as a seed.
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</p></dd></dl>
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</body>
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</html>
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