163 lines
7.8 KiB
HTML
163 lines
7.8 KiB
HTML
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<head>
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<title>GNU Compiler Collection (GCC) Internals: Floating Point</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals: Floating Point">
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<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Floating Point">
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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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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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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">17.22 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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