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123 lines
4.8 KiB
HTML
123 lines
4.8 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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version published by the Free Software Foundation; with no Invariant Sections,
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GNU Free Documentation License. -->
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<head>
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<title>Variable Conventions (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="Variable Conventions (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="GMP-Basics.html#GMP-Basics" rel="up" title="GMP Basics">
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<link href="Parameter-Conventions.html#Parameter-Conventions" rel="next" title="Parameter Conventions">
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</head>
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<body lang="en">
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<a name="Variable-Conventions"></a>
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<div class="header">
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<p>
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Next: <a href="Parameter-Conventions.html#Parameter-Conventions" accesskey="n" rel="next">Parameter Conventions</a>, Previous: <a href="Function-Classes.html#Function-Classes" accesskey="p" rel="prev">Function Classes</a>, Up: <a href="GMP-Basics.html#GMP-Basics" accesskey="u" rel="up">GMP Basics</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="Variable-Conventions-1"></a>
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<h3 class="section">3.4 Variable Conventions</h3>
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<a name="index-Variable-conventions"></a>
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<a name="index-Conventions-for-variables"></a>
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<p>GMP functions generally have output arguments before input arguments. This
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notation is by analogy with the assignment operator. The BSD MP compatibility
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functions are exceptions, having the output arguments last.
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</p>
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<p>GMP lets you use the same variable for both input and output in one call. For
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example, the main function for integer multiplication, <code>mpz_mul</code>, can be
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used to square <code>x</code> and put the result back in <code>x</code> with
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</p>
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<div class="example">
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<pre class="example">mpz_mul (x, x, x);
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</pre></div>
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<p>Before you can assign to a GMP variable, you need to initialize it by calling
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one of the special initialization functions. When you’re done with a
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variable, you need to clear it out, using one of the functions for that
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purpose. Which function to use depends on the type of variable. See the
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chapters on integer functions, rational number functions, and floating-point
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functions for details.
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</p>
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<p>A variable should only be initialized once, or at least cleared between each
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initialization. After a variable has been initialized, it may be assigned to
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any number of times.
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</p>
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<p>For efficiency reasons, avoid excessive initializing and clearing. In
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general, initialize near the start of a function and clear near the end. 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">void
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foo (void)
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{
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mpz_t n;
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int i;
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mpz_init (n);
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for (i = 1; i < 100; i++)
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{
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mpz_mul (n, …);
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mpz_fdiv_q (n, …);
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…
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}
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mpz_clear (n);
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}
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</pre></div>
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</body>
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</html>
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