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156 lines
8.2 KiB
HTML
156 lines
8.2 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>Converting Floats (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="Converting Floats (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="Floating_002dpoint-Functions.html#Floating_002dpoint-Functions" rel="up" title="Floating-point Functions">
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<link href="Float-Arithmetic.html#Float-Arithmetic" rel="next" title="Float Arithmetic">
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<link href="Simultaneous-Float-Init-_0026-Assign.html#Simultaneous-Float-Init-_0026-Assign" rel="prev" title="Simultaneous Float Init & Assign">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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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="Converting-Floats"></a>
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<div class="header">
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<p>
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Next: <a href="Float-Arithmetic.html#Float-Arithmetic" accesskey="n" rel="next">Float Arithmetic</a>, Previous: <a href="Simultaneous-Float-Init-_0026-Assign.html#Simultaneous-Float-Init-_0026-Assign" accesskey="p" rel="prev">Simultaneous Float Init & Assign</a>, Up: <a href="Floating_002dpoint-Functions.html#Floating_002dpoint-Functions" accesskey="u" rel="up">Floating-point 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="Conversion-Functions-2"></a>
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<h3 class="section">7.4 Conversion Functions</h3>
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<a name="index-Float-conversion-functions"></a>
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<a name="index-Conversion-functions-2"></a>
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<dl>
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<dt><a name="index-mpf_005fget_005fd"></a>Function: <em>double</em> <strong>mpf_get_d</strong> <em>(const mpf_t <var>op</var>)</em></dt>
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<dd><p>Convert <var>op</var> to a <code>double</code>, truncating if necessary (i.e. rounding
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towards zero).
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</p>
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<p>If the exponent in <var>op</var> is too big or too small to fit a <code>double</code>
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then the result is system dependent. For too big an infinity is returned when
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available. For too small <em>0.0</em> is normally returned. Hardware overflow,
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underflow and denorm traps may or may not occur.
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpf_005fget_005fd_005f2exp"></a>Function: <em>double</em> <strong>mpf_get_d_2exp</strong> <em>(signed long int *<var>exp</var>, const mpf_t <var>op</var>)</em></dt>
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<dd><p>Convert <var>op</var> to a <code>double</code>, truncating if necessary (i.e. rounding
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towards zero), and with an exponent returned separately.
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</p>
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<p>The return value is in the range <em>0.5<=abs(<var>d</var>)<1</em> and the
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exponent is stored to <code>*<var>exp</var></code>. <em><var>d</var> * 2^<var>exp</var></em> is the (truncated) <var>op</var> value. If <var>op</var> is zero,
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the return is <em>0.0</em> and 0 is stored to <code>*<var>exp</var></code>.
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</p>
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<a name="index-frexp-1"></a>
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<p>This is similar to the standard C <code>frexp</code> function (see <a href="http://www.gnu.org/software/libc/manual/html_node/Normalization-Functions.html#Normalization-Functions">Normalization
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Functions</a> in <cite>The GNU C Library Reference Manual</cite>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpf_005fget_005fsi"></a>Function: <em>long</em> <strong>mpf_get_si</strong> <em>(const mpf_t <var>op</var>)</em></dt>
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<dt><a name="index-mpf_005fget_005fui"></a>Function: <em>unsigned long</em> <strong>mpf_get_ui</strong> <em>(const mpf_t <var>op</var>)</em></dt>
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<dd><p>Convert <var>op</var> to a <code>long</code> or <code>unsigned long</code>, truncating any
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fraction part. If <var>op</var> is too big for the return type, the result is
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undefined.
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</p>
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<p>See also <code>mpf_fits_slong_p</code> and <code>mpf_fits_ulong_p</code>
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(see <a href="Miscellaneous-Float-Functions.html#Miscellaneous-Float-Functions">Miscellaneous Float Functions</a>).
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</p></dd></dl>
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<dl>
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<dt><a name="index-mpf_005fget_005fstr"></a>Function: <em>char *</em> <strong>mpf_get_str</strong> <em>(char *<var>str</var>, mp_exp_t *<var>expptr</var>, int <var>base</var>, size_t <var>n_digits</var>, const mpf_t <var>op</var>)</em></dt>
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<dd><p>Convert <var>op</var> to a string of digits in base <var>base</var>. The base argument
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may vary from 2 to 62 or from -2 to -36. Up to <var>n_digits</var>
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digits will be generated. Trailing zeros are not returned. No more digits
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than can be accurately represented by <var>op</var> are ever generated. If
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<var>n_digits</var> is 0 then that accurate maximum number of digits are generated.
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</p>
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<p>For <var>base</var> in the range 2..36, digits and lower-case letters are used; for
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-2..-36, digits and upper-case letters are used; for 37..62,
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digits, upper-case letters, and lower-case letters (in that significance order)
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are used.
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</p>
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<p>If <var>str</var> is <code>NULL</code>, the result string is allocated using the current
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allocation function (see <a href="Custom-Allocation.html#Custom-Allocation">Custom Allocation</a>). The block will be
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<code>strlen(str)+1</code> bytes, that being exactly enough for the string and
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null-terminator.
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</p>
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<p>If <var>str</var> is not <code>NULL</code>, it should point to a block of
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<em><var>n_digits</var> + 2</em> bytes, that being enough for the mantissa, a
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possible minus sign, and a null-terminator. When <var>n_digits</var> is 0 to get
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all significant digits, an application won’t be able to know the space
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required, and <var>str</var> should be <code>NULL</code> in that case.
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</p>
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<p>The generated string is a fraction, with an implicit radix point immediately
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to the left of the first digit. The applicable exponent is written through
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the <var>expptr</var> pointer. For example, the number 3.1416 would be returned as
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string <code>"31416"</code> and exponent 1.
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</p>
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<p>When <var>op</var> is zero, an empty string is produced and the exponent returned
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is 0.
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</p>
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<p>A pointer to the result string is returned, being either the allocated block
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or the given <var>str</var>.
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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="Float-Arithmetic.html#Float-Arithmetic" accesskey="n" rel="next">Float Arithmetic</a>, Previous: <a href="Simultaneous-Float-Init-_0026-Assign.html#Simultaneous-Float-Init-_0026-Assign" accesskey="p" rel="prev">Simultaneous Float Init & Assign</a>, Up: <a href="Floating_002dpoint-Functions.html#Floating_002dpoint-Functions" accesskey="u" rel="up">Floating-point 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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