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140 lines
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140 lines
6.0 KiB
HTML
4 years ago
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<html lang="en">
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<title>Floating point implementation - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="C-Implementation.html#C-Implementation" title="C Implementation">
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<link rel="prev" href="Integers-implementation.html#Integers-implementation" title="Integers implementation">
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<link rel="next" href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" title="Arrays and pointers implementation">
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Copyright (C) 1988-2015 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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="Floating-point-implementation"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation">Arrays and pointers implementation</a>,
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Previous: <a rel="previous" accesskey="p" href="Integers-implementation.html#Integers-implementation">Integers implementation</a>,
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Up: <a rel="up" accesskey="u" href="C-Implementation.html#C-Implementation">C Implementation</a>
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<hr>
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</div>
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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 </cite><code><math.h></code><cite> and </cite><code><complex.h></code><cite> 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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<li><cite>The rounding behaviors characterized by non-standard values
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of </cite><code>FLT_ROUNDS</code><cite>
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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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<li><cite>The evaluation methods characterized by non-standard negative
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values of </cite><code>FLT_EVAL_METHOD</code><cite> (C99 and C11 5.2.4.2.2).</cite>
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<p>GCC does not use such values.
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<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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<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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<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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<li><cite>Whether and how floating expressions are contracted when not
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disallowed by the </cite><code>FP_CONTRACT</code><cite> pragma (C99 and C11 6.5).</cite>
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<p>Expressions are currently only contracted if <samp><span class="option">-ffp-contract=fast</span></samp>,
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<samp><span class="option">-funsafe-math-optimizations</span></samp> or <samp><span class="option">-ffast-math</span></samp> are used.
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This is subject to change.
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<li><cite>The default state for the </cite><code>FENV_ACCESS</code><cite> 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><span class="option">-frounding-math</span></samp> is used in which case it is “on”.
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<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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<li><cite>The default state for the </cite><code>FP_CONTRACT</code><cite> 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><span class="option">-ffp-contract=fast</span></samp>,
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<samp><span class="option">-funsafe-math-optimizations</span></samp> or <samp><span class="option">-ffast-math</span></samp> are used.
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This is subject to change.
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<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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<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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</ul>
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</body></html>
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