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78 lines
3.7 KiB
HTML
78 lines
3.7 KiB
HTML
4 years ago
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<title>Hex Floats - 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 rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions">
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<link rel="prev" href="Decimal-Float.html#Decimal-Float" title="Decimal Float">
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<link rel="next" href="Fixed_002dPoint.html#Fixed_002dPoint" title="Fixed-Point">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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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="Hex-Floats"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Fixed_002dPoint.html#Fixed_002dPoint">Fixed-Point</a>,
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Previous: <a rel="previous" accesskey="p" href="Decimal-Float.html#Decimal-Float">Decimal Float</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<hr>
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</div>
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<h3 class="section">6.14 Hex Floats</h3>
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<p><a name="index-hex-floats-2935"></a>
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ISO C99 supports floating-point numbers written not only in the usual
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decimal notation, such as <code>1.55e1</code>, but also numbers such as
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<code>0x1.fp3</code> written in hexadecimal format. As a GNU extension, GCC
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supports this in C90 mode (except in some cases when strictly
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conforming) and in C++. In that format the
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‘<samp><span class="samp">0x</span></samp>’ hex introducer and the ‘<samp><span class="samp">p</span></samp>’ or ‘<samp><span class="samp">P</span></samp>’ exponent field are
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mandatory. The exponent is a decimal number that indicates the power of
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2 by which the significant part is multiplied. Thus ‘<samp><span class="samp">0x1.f</span></samp>’ is
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1 15/16,
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‘<samp><span class="samp">p3</span></samp>’ multiplies it by 8, and the value of <code>0x1.fp3</code>
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is the same as <code>1.55e1</code>.
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<p>Unlike for floating-point numbers in the decimal notation the exponent
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is always required in the hexadecimal notation. Otherwise the compiler
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would not be able to resolve the ambiguity of, e.g., <code>0x1.f</code>. This
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could mean <code>1.0f</code> or <code>1.9375</code> since ‘<samp><span class="samp">f</span></samp>’ is also the
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extension for floating-point constants of type <code>float</code>.
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</body></html>
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