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162 lines
7.8 KiB
HTML
162 lines
7.8 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 (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Floating Point (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Floating Point (GNU Compiler Collection (GCC) Internals)">
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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="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">
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<link href="Mode-Switching.html#Mode-Switching" rel="next" title="Mode Switching">
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<link href="VMS-Debug.html#VMS-Debug" rel="prev" title="VMS Debug">
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<style type="text/css">
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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="Floating-Point"></a>
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<div class="header">
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<p>
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Next: <a href="Mode-Switching.html#Mode-Switching" accesskey="n" rel="next">Mode Switching</a>, Previous: <a href="Debugging-Info.html#Debugging-Info" accesskey="p" rel="prev">Debugging Info</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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="Cross-Compilation-and-Floating-Point"></a>
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<h3 class="section">18.22 Cross Compilation and Floating Point</h3>
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<a name="index-cross-compilation-and-floating-point"></a>
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<a name="index-floating-point-and-cross-compilation"></a>
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<p>While all modern machines use twos-complement representation for integers,
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there are a variety of representations for floating point numbers. This
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means that in a cross-compiler the representation of floating point numbers
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in the compiled program may be different from that used in the machine
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doing the compilation.
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</p>
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<p>Because different representation systems may offer different amounts of
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range and precision, all floating point constants must be represented in
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the target machine’s format. Therefore, the cross compiler cannot
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safely use the host machine’s floating point arithmetic; it must emulate
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the target’s arithmetic. To ensure consistency, GCC always uses
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emulation to work with floating point values, even when the host and
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target floating point formats are identical.
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</p>
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<p>The following macros are provided by <samp>real.h</samp> for the compiler to
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use. All parts of the compiler which generate or optimize
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floating-point calculations must use these macros. They may evaluate
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their operands more than once, so operands must not have side effects.
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</p>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fTYPE"></a>Macro: <strong>REAL_VALUE_TYPE</strong></dt>
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<dd><p>The C data type to be used to hold a floating point value in the target
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machine’s format. Typically this is a <code>struct</code> containing an
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array of <code>HOST_WIDE_INT</code>, but all code should treat it as an opaque
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quantity.
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fFIX"></a>Macro: <em>HOST_WIDE_INT</em> <strong>REAL_VALUE_FIX</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
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<dd><p>Truncates <var>x</var> to a signed integer, rounding toward zero.
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fUNSIGNED_005fFIX"></a>Macro: <em>unsigned HOST_WIDE_INT</em> <strong>REAL_VALUE_UNSIGNED_FIX</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
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<dd><p>Truncates <var>x</var> to an unsigned integer, rounding toward zero. If
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<var>x</var> is negative, returns zero.
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fATOF"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_ATOF</strong> <em>(const char *<var>string</var>, machine_mode <var>mode</var>)</em></dt>
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<dd><p>Converts <var>string</var> into a floating point number in the target machine’s
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representation for mode <var>mode</var>. This routine can handle both
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decimal and hexadecimal floating point constants, using the syntax
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defined by the C language for both.
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fNEGATIVE"></a>Macro: <em>int</em> <strong>REAL_VALUE_NEGATIVE</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
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<dd><p>Returns 1 if <var>x</var> is negative (including negative zero), 0 otherwise.
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fISINF"></a>Macro: <em>int</em> <strong>REAL_VALUE_ISINF</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
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<dd><p>Determines whether <var>x</var> represents infinity (positive or negative).
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fISNAN"></a>Macro: <em>int</em> <strong>REAL_VALUE_ISNAN</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
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<dd><p>Determines whether <var>x</var> represents a “NaN” (not-a-number).
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fNEGATE"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_NEGATE</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
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<dd><p>Returns the negative of the floating point value <var>x</var>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-REAL_005fVALUE_005fABS"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_ABS</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
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<dd><p>Returns the absolute value of <var>x</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="Mode-Switching.html#Mode-Switching" accesskey="n" rel="next">Mode Switching</a>, Previous: <a href="Debugging-Info.html#Debugging-Info" accesskey="p" rel="prev">Debugging Info</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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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