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184 lines
8.9 KiB
HTML
184 lines
8.9 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>Custom Interface (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="Custom Interface (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-Interface.html#MPFR-Interface" rel="up" title="MPFR Interface">
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<link href="Internals.html#Internals" rel="next" title="Internals">
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<link href="Compatibility-with-MPF.html#Compatibility-with-MPF" rel="prev" title="Compatibility with MPF">
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<style type="text/css">
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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="Custom-Interface"></a>
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<div class="header">
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<p>
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Next: <a href="Internals.html#Internals" accesskey="n" rel="next">Internals</a>, Previous: <a href="Compatibility-with-MPF.html#Compatibility-with-MPF" accesskey="p" rel="prev">Compatibility with MPF</a>, Up: <a href="MPFR-Interface.html#MPFR-Interface" accesskey="u" rel="up">MPFR Interface</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="index-Custom-interface"></a>
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<a name="Custom-Interface-1"></a>
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<h3 class="section">5.15 Custom Interface</h3>
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<p>Some applications use a stack to handle the memory and their objects.
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However, the MPFR memory design is not well suited for such a thing. So that
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such applications are able to use MPFR, an auxiliary memory interface has
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been created: the Custom Interface.
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</p>
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<p>The following interface allows one to use MPFR in two ways:
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</p>
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<ul>
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<li> Either directly store a floating-point number as a <code>mpfr_t</code>
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on the stack.
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</li><li> Either store its own representation on the
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stack and construct a new temporary <code>mpfr_t</code> each time it is needed.
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</li></ul>
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<p>Nothing has to be done to destroy the floating-point
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numbers except garbaging the used
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memory: all the memory management (allocating, destroying, garbaging) is left
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to the application.
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</p>
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<p>Each function in this interface is also implemented as a macro for
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efficiency reasons: for example <code>mpfr_custom_init (s, p)</code>
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uses the macro, while <code>(mpfr_custom_init) (s, p)</code> uses the function.
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</p>
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<p>Note 1: MPFR functions may still initialize temporary floating-point numbers
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using <code>mpfr_init</code> and similar functions. See Custom Allocation (GNU MP).
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</p>
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<p>Note 2: MPFR functions may use the cached functions (<code>mpfr_const_pi</code> for
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example), even if they are not explicitly called. You have to call
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<code>mpfr_free_cache</code> each time you garbage the memory iff <code>mpfr_init</code>,
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through GMP Custom Allocation, allocates its memory on the application stack.
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</p>
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<dl>
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<dt><a name="index-mpfr_005fcustom_005fget_005fsize"></a>Function: <em>size_t</em> <strong>mpfr_custom_get_size</strong> <em>(mpfr_prec_t <var>prec</var>)</em></dt>
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<dd><p>Return the needed size in bytes to store the significand of a floating-point
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number of precision <var>prec</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpfr_005fcustom_005finit"></a>Function: <em>void</em> <strong>mpfr_custom_init</strong> <em>(void *<var>significand</var>, mpfr_prec_t <var>prec</var>)</em></dt>
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<dd><p>Initialize a significand of precision <var>prec</var>, where
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<var>significand</var> must be an area of <code>mpfr_custom_get_size (prec)</code> bytes
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at least and be suitably aligned for an array of <code>mp_limb_t</code> (GMP type,
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see <a href="Internals.html#Internals">Internals</a>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpfr_005fcustom_005finit_005fset"></a>Function: <em>void</em> <strong>mpfr_custom_init_set</strong> <em>(mpfr_t <var>x</var>, int <var>kind</var>, mpfr_exp_t <var>exp</var>, mpfr_prec_t <var>prec</var>, void *<var>significand</var>)</em></dt>
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<dd><p>Perform a dummy initialization of a <code>mpfr_t</code> and set it to:
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</p><ul>
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<li> if <code>ABS(kind) == MPFR_NAN_KIND</code>, <var>x</var> is set to NaN;
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</li><li> if <code>ABS(kind) == MPFR_INF_KIND</code>, <var>x</var> is set to the infinity
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of sign <code>sign(kind)</code>;
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</li><li> if <code>ABS(kind) == MPFR_ZERO_KIND</code>, <var>x</var> is set to the zero of
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sign <code>sign(kind)</code>;
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</li><li> if <code>ABS(kind) == MPFR_REGULAR_KIND</code>, <var>x</var> is set to a regular
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number: <code>x = sign(kind)*significand*2^exp</code>.
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</li></ul>
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<p>In all cases, it uses <var>significand</var> directly for further computing
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involving <var>x</var>. It will not allocate anything.
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A floating-point number initialized with this function cannot be resized using
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<code>mpfr_set_prec</code> or <code>mpfr_prec_round</code>,
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or cleared using <code>mpfr_clear</code>!
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The <var>significand</var> must have been initialized with <code>mpfr_custom_init</code>
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using the same precision <var>prec</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpfr_005fcustom_005fget_005fkind"></a>Function: <em>int</em> <strong>mpfr_custom_get_kind</strong> <em>(mpfr_t <var>x</var>)</em></dt>
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<dd><p>Return the current kind of a <code>mpfr_t</code> as created by
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<code>mpfr_custom_init_set</code>.
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The behavior of this function for any <code>mpfr_t</code> not initialized
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with <code>mpfr_custom_init_set</code> is undefined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpfr_005fcustom_005fget_005fsignificand"></a>Function: <em>void *</em> <strong>mpfr_custom_get_significand</strong> <em>(mpfr_t <var>x</var>)</em></dt>
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<dd><p>Return a pointer to the significand used by a <code>mpfr_t</code> initialized with
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<code>mpfr_custom_init_set</code>.
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The behavior of this function for any <code>mpfr_t</code> not initialized
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with <code>mpfr_custom_init_set</code> is undefined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpfr_005fcustom_005fget_005fexp"></a>Function: <em>mpfr_exp_t</em> <strong>mpfr_custom_get_exp</strong> <em>(mpfr_t <var>x</var>)</em></dt>
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<dd><p>Return the exponent of <var>x</var>, assuming that <var>x</var> is a non-zero ordinary
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number. The return value for NaN, Infinity or zero is unspecified but does not
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produce any trap.
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The behavior of this function for any <code>mpfr_t</code> not initialized
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with <code>mpfr_custom_init_set</code> is undefined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpfr_005fcustom_005fmove"></a>Function: <em>void</em> <strong>mpfr_custom_move</strong> <em>(mpfr_t <var>x</var>, void *<var>new_position</var>)</em></dt>
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<dd><p>Inform MPFR that the significand of <var>x</var> has moved due to a garbage collect
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and update its new position to <code>new_position</code>.
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However the application has to move the significand and the <code>mpfr_t</code>
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itself.
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The behavior of this function for any <code>mpfr_t</code> not initialized
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with <code>mpfr_custom_init_set</code> is undefined.
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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="Internals.html#Internals" accesskey="n" rel="next">Internals</a>, Previous: <a href="Compatibility-with-MPF.html#Compatibility-with-MPF" accesskey="p" rel="prev">Compatibility with MPF</a>, Up: <a href="MPFR-Interface.html#MPFR-Interface" accesskey="u" rel="up">MPFR Interface</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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