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<title>Using the GNU Compiler Collection (GCC): Floating point implementation</title>
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<a name="Floating-point-implementation"></a>
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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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<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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