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100 lines
4.5 KiB
HTML
100 lines
4.5 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 documents how to install and use the Multiple Precision
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Floating-Point Reliable Library, version 3.1.4.
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Copyright 1991, 1993-2016 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 1.2 or any later
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version published by the Free Software Foundation; with no Invariant Sections,
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with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the
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license is included in 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>MPFR Variable Conventions (GNU MPFR 3.1.4)</title>
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<meta name="description" content="How to install and use GNU MPFR, a library for reliable multiple precision
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floating-point arithmetic, version 3.1.4.">
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<meta name="keywords" content="MPFR Variable Conventions (GNU MPFR 3.1.4)">
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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=utf-8">
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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="MPFR-Basics.html#MPFR-Basics" rel="up" title="MPFR Basics">
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<link href="Rounding-Modes.html#Rounding-Modes" rel="next" title="Rounding Modes">
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<link href="Nomenclature-and-Types.html#Nomenclature-and-Types" rel="prev" title="Nomenclature and Types">
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</style>
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</head>
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<body lang="en">
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<a name="MPFR-Variable-Conventions"></a>
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<div class="header">
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<p>
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Next: <a href="Rounding-Modes.html#Rounding-Modes" accesskey="n" rel="next">Rounding Modes</a>, Previous: <a href="Nomenclature-and-Types.html#Nomenclature-and-Types" accesskey="p" rel="prev">Nomenclature and Types</a>, Up: <a href="MPFR-Basics.html#MPFR-Basics" accesskey="u" rel="up">MPFR 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="MPFR-Variable-Conventions-1"></a>
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<h3 class="section">4.3 MPFR Variable Conventions</h3>
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<p>Before you can assign to an MPFR 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.
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A variable should only be initialized once, or at least cleared out between
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each initialization. After a variable has been initialized, it may be
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assigned to any number of times.
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For efficiency reasons, avoid to initialize and clear out a variable in loops.
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Instead, initialize it before entering the loop, and clear it out after the
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loop has exited.
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You do not need to be concerned about allocating additional space for MPFR
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variables, since any variable has a significand of fixed size.
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Hence unless you change its precision, or clear and reinitialize it,
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a floating-point variable will have the same allocated space during all its
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life.
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</p>
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<p>As a general rule, all MPFR functions expect output arguments before input
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arguments. This notation is based on an analogy with the assignment operator.
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MPFR allows you to use the same variable for both input and output in the same
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expression. For example, the main function for floating-point multiplication,
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<code>mpfr_mul</code>, can be used like this: <code>mpfr_mul (x, x, x, rnd)</code>.
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This
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computes the square of <var>x</var> with rounding mode <code>rnd</code>
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and puts the result back in <var>x</var>.
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</p>
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</body>
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</html>
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