138 lines
6.4 KiB
HTML
138 lines
6.4 KiB
HTML
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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) 1988-2016 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 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using the GNU Compiler Collection (GCC): Decimal Float</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC): Decimal Float">
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<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Decimal Float">
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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="Hex-Floats.html#Hex-Floats" rel="next" title="Hex Floats">
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<link href="Half_002dPrecision.html#Half_002dPrecision" rel="prev" title="Half-Precision">
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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" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Decimal-Float"></a>
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<div class="header">
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<p>
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Next: <a href="Hex-Floats.html#Hex-Floats" accesskey="n" rel="next">Hex Floats</a>, Previous: <a href="Half_002dPrecision.html#Half_002dPrecision" accesskey="p" rel="prev">Half-Precision</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="Decimal-Floating-Types"></a>
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<h3 class="section">6.13 Decimal Floating Types</h3>
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<a name="index-decimal-floating-types"></a>
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<a name="index-_005fDecimal32-data-type"></a>
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<a name="index-_005fDecimal64-data-type"></a>
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<a name="index-_005fDecimal128-data-type"></a>
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<a name="index-df-integer-suffix"></a>
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<a name="index-dd-integer-suffix"></a>
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<a name="index-dl-integer-suffix"></a>
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<a name="index-DF-integer-suffix"></a>
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<a name="index-DD-integer-suffix"></a>
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<a name="index-DL-integer-suffix"></a>
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<p>As an extension, GNU C supports decimal floating types as
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defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal
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floating types in GCC will evolve as the draft technical report changes.
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Calling conventions for any target might also change. Not all targets
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support decimal floating types.
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</p>
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<p>The decimal floating types are <code>_Decimal32</code>, <code>_Decimal64</code>, and
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<code>_Decimal128</code>. They use a radix of ten, unlike the floating types
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<code>float</code>, <code>double</code>, and <code>long double</code> whose radix is not
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specified by the C standard but is usually two.
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</p>
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<p>Support for decimal floating types includes the arithmetic operators
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add, subtract, multiply, divide; unary arithmetic operators;
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relational operators; equality operators; and conversions to and from
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integer and other floating types. Use a suffix ‘<samp>df</samp>’ or
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‘<samp>DF</samp>’ in a literal constant of type <code>_Decimal32</code>, ‘<samp>dd</samp>’
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or ‘<samp>DD</samp>’ for <code>_Decimal64</code>, and ‘<samp>dl</samp>’ or ‘<samp>DL</samp>’ for
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<code>_Decimal128</code>.
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</p>
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<p>GCC support of decimal float as specified by the draft technical report
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is incomplete:
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</p>
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<ul>
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<li> When the value of a decimal floating type cannot be represented in the
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integer type to which it is being converted, the result is undefined
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rather than the result value specified by the draft technical report.
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</li><li> GCC does not provide the C library functionality associated with
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<samp>math.h</samp>, <samp>fenv.h</samp>, <samp>stdio.h</samp>, <samp>stdlib.h</samp>, and
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<samp>wchar.h</samp>, which must come from a separate C library implementation.
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Because of this the GNU C compiler does not define macro
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<code>__STDC_DEC_FP__</code> to indicate that the implementation conforms to
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the technical report.
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</li></ul>
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<p>Types <code>_Decimal32</code>, <code>_Decimal64</code>, and <code>_Decimal128</code>
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are supported by the DWARF debug information format.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Hex-Floats.html#Hex-Floats" accesskey="n" rel="next">Hex Floats</a>, Previous: <a href="Half_002dPrecision.html#Half_002dPrecision" accesskey="p" rel="prev">Half-Precision</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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</body>
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</html>
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