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166 lines
8.5 KiB
HTML
166 lines
8.5 KiB
HTML
<!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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GNU Free Documentation License. -->
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<head>
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<title>Integer Import and Export (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="Integer Import and Export (GNU MP 6.1.0)">
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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="Miscellaneous-Integer-Functions.html#Miscellaneous-Integer-Functions" rel="next" title="Miscellaneous Integer Functions">
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<link href="Integer-Random-Numbers.html#Integer-Random-Numbers" rel="prev" title="Integer Random Numbers">
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</head>
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<body lang="en">
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<a name="Integer-Import-and-Export"></a>
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<div class="header">
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<p>
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Next: <a href="Miscellaneous-Integer-Functions.html#Miscellaneous-Integer-Functions" accesskey="n" rel="next">Miscellaneous Integer Functions</a>, Previous: <a href="Integer-Random-Numbers.html#Integer-Random-Numbers" accesskey="p" rel="prev">Integer Random Numbers</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="Integer-Import-and-Export-1"></a>
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<h3 class="section">5.14 Integer Import and Export</h3>
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<p><code>mpz_t</code> variables can be converted to and from arbitrary words of binary
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data with the following functions.
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</p>
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<dl>
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<dt><a name="index-mpz_005fimport"></a>Function: <em>void</em> <strong>mpz_import</strong> <em>(mpz_t <var>rop</var>, size_t <var>count</var>, int <var>order</var>, size_t <var>size</var>, int <var>endian</var>, size_t <var>nails</var>, const void *<var>op</var>)</em></dt>
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<dd><a name="index-Integer-import"></a>
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<a name="index-Import"></a>
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<p>Set <var>rop</var> from an array of word data at <var>op</var>.
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</p>
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<p>The parameters specify the format of the data. <var>count</var> many words are
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read, each <var>size</var> bytes. <var>order</var> can be 1 for most significant word
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first or -1 for least significant first. Within each word <var>endian</var> can be
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1 for most significant byte first, -1 for least significant first, or 0 for
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the native endianness of the host CPU. The most significant <var>nails</var> bits
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of each word are skipped, this can be 0 to use the full words.
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</p>
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<p>There is no sign taken from the data, <var>rop</var> will simply be a positive
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integer. An application can handle any sign itself, and apply it for instance
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with <code>mpz_neg</code>.
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</p>
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<p>There are no data alignment restrictions on <var>op</var>, any address is allowed.
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</p>
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<p>Here’s an example converting an array of <code>unsigned long</code> data, most
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significant element first, and host byte order within each value.
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</p>
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<div class="example">
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<pre class="example">unsigned long a[20];
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/* Initialize <var>z</var> and <var>a</var> */
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mpz_import (z, 20, 1, sizeof(a[0]), 0, 0, a);
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</pre></div>
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<p>This example assumes the full <code>sizeof</code> bytes are used for data in the
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given type, which is usually true, and certainly true for <code>unsigned long</code>
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everywhere we know of. However on Cray vector systems it may be noted that
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<code>short</code> and <code>int</code> are always stored in 8 bytes (and with
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<code>sizeof</code> indicating that) but use only 32 or 46 bits. The <var>nails</var>
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feature can account for this, by passing for instance
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<code>8*sizeof(int)-INT_BIT</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpz_005fexport"></a>Function: <em>void *</em> <strong>mpz_export</strong> <em>(void *<var>rop</var>, size_t *<var>countp</var>, int <var>order</var>, size_t <var>size</var>, int <var>endian</var>, size_t <var>nails</var>, const mpz_t <var>op</var>)</em></dt>
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<dd><a name="index-Integer-export"></a>
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<a name="index-Export"></a>
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<p>Fill <var>rop</var> with word data from <var>op</var>.
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</p>
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<p>The parameters specify the format of the data produced. Each word will be
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<var>size</var> bytes and <var>order</var> can be 1 for most significant word first or
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-1 for least significant first. Within each word <var>endian</var> can be 1 for
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most significant byte first, -1 for least significant first, or 0 for the
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native endianness of the host CPU. The most significant <var>nails</var> bits of
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each word are unused and set to zero, this can be 0 to produce full words.
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</p>
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<p>The number of words produced is written to <code>*<var>countp</var></code>, or
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<var>countp</var> can be <code>NULL</code> to discard the count. <var>rop</var> must have
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enough space for the data, or if <var>rop</var> is <code>NULL</code> then a result array
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of the necessary size is allocated using the current GMP allocation function
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(see <a href="Custom-Allocation.html#Custom-Allocation">Custom Allocation</a>). In either case the return value is the
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destination used, either <var>rop</var> or the allocated block.
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</p>
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<p>If <var>op</var> is non-zero then the most significant word produced will be
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non-zero. If <var>op</var> is zero then the count returned will be zero and
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nothing written to <var>rop</var>. If <var>rop</var> is <code>NULL</code> in this case, no
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block is allocated, just <code>NULL</code> is returned.
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</p>
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<p>The sign of <var>op</var> is ignored, just the absolute value is exported. An
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application can use <code>mpz_sgn</code> to get the sign and handle it as desired.
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(see <a href="Integer-Comparisons.html#Integer-Comparisons">Integer Comparisons</a>)
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</p>
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<p>There are no data alignment restrictions on <var>rop</var>, any address is allowed.
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</p>
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<p>When an application is allocating space itself the required size can be
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determined with a calculation like the following. Since <code>mpz_sizeinbase</code>
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always returns at least 1, <code>count</code> here will be at least one, which
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avoids any portability problems with <code>malloc(0)</code>, though if <code>z</code> is
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zero no space at all is actually needed (or written).
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</p>
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<div class="example">
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<pre class="example">numb = 8*size - nail;
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count = (mpz_sizeinbase (z, 2) + numb-1) / numb;
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p = malloc (count * size);
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</pre></div>
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</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="Miscellaneous-Integer-Functions.html#Miscellaneous-Integer-Functions" accesskey="n" rel="next">Miscellaneous Integer Functions</a>, Previous: <a href="Integer-Random-Numbers.html#Integer-Random-Numbers" accesskey="p" rel="prev">Integer Random Numbers</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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