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170 lines
7.4 KiB
HTML
170 lines
7.4 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>Floating point implementation (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Floating point implementation (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Floating point implementation (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-Implementation.html#C-Implementation" rel="up" title="C Implementation">
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<link href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" rel="next" title="Arrays and pointers implementation">
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<link href="Integers-implementation.html#Integers-implementation" rel="prev" title="Integers implementation">
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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="Floating-point-implementation"></a>
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<div class="header">
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<p>
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Next: <a href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" accesskey="n" rel="next">Arrays and pointers implementation</a>, Previous: <a href="Integers-implementation.html#Integers-implementation" accesskey="p" rel="prev">Integers implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</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="Floating-Point"></a>
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<h3 class="section">4.6 Floating Point</h3>
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<ul>
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<li> <cite>The accuracy of the floating-point operations and of the library
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functions in <code><math.h></code> and <code><complex.h></code> that return floating-point
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results (C90, C99 and C11 5.2.4.2.2).</cite>
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<p>The accuracy is unknown.
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</p>
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</li><li> <cite>The rounding behaviors characterized by non-standard values
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of <code>FLT_ROUNDS</code>
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(C90, C99 and C11 5.2.4.2.2).</cite>
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<p>GCC does not use such values.
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</p>
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</li><li> <cite>The evaluation methods characterized by non-standard negative
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values of <code>FLT_EVAL_METHOD</code> (C99 and C11 5.2.4.2.2).</cite>
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<p>GCC does not use such values.
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</p>
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</li><li> <cite>The direction of rounding when an integer is converted to a
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floating-point number that cannot exactly represent the original
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value (C90 6.2.1.3, C99 and C11 6.3.1.4).</cite>
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<p>C99 Annex F is followed.
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</p>
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</li><li> <cite>The direction of rounding when a floating-point number is
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converted to a narrower floating-point number (C90 6.2.1.4, C99 and C11
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6.3.1.5).</cite>
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<p>C99 Annex F is followed.
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</p>
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</li><li> <cite>How the nearest representable value or the larger or smaller
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representable value immediately adjacent to the nearest representable
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value is chosen for certain floating constants (C90 6.1.3.1, C99 and C11
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6.4.4.2).</cite>
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<p>C99 Annex F is followed.
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</p>
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</li><li> <cite>Whether and how floating expressions are contracted when not
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disallowed by the <code>FP_CONTRACT</code> pragma (C99 and C11 6.5).</cite>
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<p>Expressions are currently only contracted if <samp>-ffp-contract=fast</samp>,
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<samp>-funsafe-math-optimizations</samp> or <samp>-ffast-math</samp> are used.
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This is subject to change.
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</p>
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</li><li> <cite>The default state for the <code>FENV_ACCESS</code> pragma (C99 and C11
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7.6.1).</cite>
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<p>This pragma is not implemented, but the default is to “off” unless
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<samp>-frounding-math</samp> is used in which case it is “on”.
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</p>
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</li><li> <cite>Additional floating-point exceptions, rounding modes, environments,
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and classifications, and their macro names (C99 and C11 7.6, C99 and
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C11 7.12).</cite>
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<p>This is dependent on the implementation of the C library, and is not
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defined by GCC itself.
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</p>
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</li><li> <cite>The default state for the <code>FP_CONTRACT</code> pragma (C99 and C11
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7.12.2).</cite>
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<p>This pragma is not implemented. Expressions are currently only
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contracted if <samp>-ffp-contract=fast</samp>,
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<samp>-funsafe-math-optimizations</samp> or <samp>-ffast-math</samp> are used.
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This is subject to change.
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</p>
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</li><li> <cite>Whether the “inexact” floating-point exception can be raised
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when the rounded result actually does equal the mathematical result
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in an IEC 60559 conformant implementation (C99 F.9).</cite>
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<p>This is dependent on the implementation of the C library, and is not
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defined by GCC itself.
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</p>
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</li><li> <cite>Whether the “underflow” (and “inexact”) floating-point
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exception can be raised when a result is tiny but not inexact in an
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IEC 60559 conformant implementation (C99 F.9).</cite>
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<p>This is dependent on the implementation of the C library, and is not
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defined by GCC itself.
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</p>
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</li></ul>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" accesskey="n" rel="next">Arrays and pointers implementation</a>, Previous: <a href="Integers-implementation.html#Integers-implementation" accesskey="p" rel="prev">Integers implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</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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