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153 lines
6.7 KiB
HTML
153 lines
6.7 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>Initializing Integers (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="Initializing Integers (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="Integer-Functions.html#Integer-Functions" rel="up" title="Integer Functions">
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<link href="Assigning-Integers.html#Assigning-Integers" rel="next" title="Assigning Integers">
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<link href="Integer-Functions.html#Integer-Functions" rel="prev" title="Integer Functions">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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kbd {font-style: oblique}
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pre.smalllisp {font-size: smaller}
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ul.no-bullet {list-style: none}
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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="Initializing-Integers"></a>
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<div class="header">
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<p>
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Next: <a href="Assigning-Integers.html#Assigning-Integers" accesskey="n" rel="next">Assigning Integers</a>, Previous: <a href="Integer-Functions.html#Integer-Functions" accesskey="p" rel="prev">Integer Functions</a>, Up: <a href="Integer-Functions.html#Integer-Functions" accesskey="u" rel="up">Integer 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="Initialization-Functions"></a>
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<h3 class="section">5.1 Initialization Functions</h3>
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<a name="index-Integer-initialization-functions"></a>
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<a name="index-Initialization-functions"></a>
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<p>The functions for integer arithmetic assume that all integer objects are
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initialized. You do that by calling the function <code>mpz_init</code>. For
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example,
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</p>
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<div class="example">
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<pre class="example">{
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mpz_t integ;
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mpz_init (integ);
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…
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mpz_add (integ, …);
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…
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mpz_sub (integ, …);
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/* Unless the program is about to exit, do ... */
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mpz_clear (integ);
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}
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</pre></div>
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<p>As you can see, you can store new values any number of times, once an
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object is initialized.
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</p>
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<dl>
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<dt><a name="index-mpz_005finit"></a>Function: <em>void</em> <strong>mpz_init</strong> <em>(mpz_t <var>x</var>)</em></dt>
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<dd><p>Initialize <var>x</var>, and set its value to 0.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpz_005finits"></a>Function: <em>void</em> <strong>mpz_inits</strong> <em>(mpz_t <var>x</var>, ...)</em></dt>
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<dd><p>Initialize a NULL-terminated list of <code>mpz_t</code> variables, and set their
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values to 0.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpz_005finit2"></a>Function: <em>void</em> <strong>mpz_init2</strong> <em>(mpz_t <var>x</var>, mp_bitcnt_t <var>n</var>)</em></dt>
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<dd><p>Initialize <var>x</var>, with space for <var>n</var>-bit numbers, and set its value to 0.
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Calling this function instead of <code>mpz_init</code> or <code>mpz_inits</code> is never
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necessary; reallocation is handled automatically by GMP when needed.
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</p>
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<p>While <var>n</var> defines the initial space, <var>x</var> will grow automatically in the
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normal way, if necessary, for subsequent values stored. <code>mpz_init2</code> makes
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it possible to avoid such reallocations if a maximum size is known in advance.
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</p>
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<p>In preparation for an operation, GMP often allocates one limb more than
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ultimately needed. To make sure GMP will not perform reallocation for
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<var>x</var>, you need to add the number of bits in <code>mp_limb_t</code> to <var>n</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpz_005fclear"></a>Function: <em>void</em> <strong>mpz_clear</strong> <em>(mpz_t <var>x</var>)</em></dt>
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<dd><p>Free the space occupied by <var>x</var>. Call this function for all <code>mpz_t</code>
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variables when you are done with them.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpz_005fclears"></a>Function: <em>void</em> <strong>mpz_clears</strong> <em>(mpz_t <var>x</var>, ...)</em></dt>
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<dd><p>Free the space occupied by a NULL-terminated list of <code>mpz_t</code> variables.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpz_005frealloc2"></a>Function: <em>void</em> <strong>mpz_realloc2</strong> <em>(mpz_t <var>x</var>, mp_bitcnt_t <var>n</var>)</em></dt>
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<dd><p>Change the space allocated for <var>x</var> to <var>n</var> bits. The value in <var>x</var>
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is preserved if it fits, or is set to 0 if not.
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</p>
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<p>Calling this function is never necessary; reallocation is handled automatically
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by GMP when needed. But this function can be used to increase the space for a
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variable in order to avoid repeated automatic reallocations, or to decrease it
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to give memory back to the heap.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Assigning-Integers.html#Assigning-Integers" accesskey="n" rel="next">Assigning Integers</a>, Previous: <a href="Integer-Functions.html#Integer-Functions" accesskey="p" rel="prev">Integer Functions</a>, Up: <a href="Integer-Functions.html#Integer-Functions" accesskey="u" rel="up">Integer 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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</body>
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</html>
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