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103 lines
4.6 KiB
HTML
103 lines
4.6 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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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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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>Hex Floats (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Hex Floats (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Hex Floats (Using the GNU Compiler Collection (GCC))">
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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="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">
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<link href="Fixed_002dPoint.html#Fixed_002dPoint" rel="next" title="Fixed-Point">
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<link href="Decimal-Float.html#Decimal-Float" rel="prev" title="Decimal Float">
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<style type="text/css">
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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="Hex-Floats"></a>
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<div class="header">
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<p>
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Next: <a href="Fixed_002dPoint.html#Fixed_002dPoint" accesskey="n" rel="next">Fixed-Point</a>, Previous: <a href="Decimal-Float.html#Decimal-Float" accesskey="p" rel="prev">Decimal Float</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Hex-Floats-1"></a>
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<h3 class="section">6.14 Hex Floats</h3>
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<a name="index-hex-floats"></a>
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<p>ISO C99 supports floating-point numbers written not only in the usual
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decimal notation, such as <code>1.55e1</code>, but also numbers such as
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<code>0x1.fp3</code> written in hexadecimal format. As a GNU extension, GCC
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supports this in C90 mode (except in some cases when strictly
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conforming) and in C++. In that format the
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‘<samp>0x</samp>’ hex introducer and the ‘<samp>p</samp>’ or ‘<samp>P</samp>’ exponent field are
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mandatory. The exponent is a decimal number that indicates the power of
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2 by which the significant part is multiplied. Thus ‘<samp>0x1.f</samp>’ is
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1 15/16,
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‘<samp>p3</samp>’ multiplies it by 8, and the value of <code>0x1.fp3</code>
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is the same as <code>1.55e1</code>.
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</p>
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<p>Unlike for floating-point numbers in the decimal notation the exponent
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is always required in the hexadecimal notation. Otherwise the compiler
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would not be able to resolve the ambiguity of, e.g., <code>0x1.f</code>. This
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could mean <code>1.0f</code> or <code>1.9375</code> since ‘<samp>f</samp>’ is also the
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extension for floating-point constants of type <code>float</code>.
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</p>
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</body>
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</html>
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