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<h3 class="section">6.13 Hex Floats</h3>

<p><a name="index-hex-floats-2246"></a>
ISO C99 supports floating-point numbers written not only in the usual
decimal notation, such as <code>1.55e1</code>, but also numbers such as
<code>0x1.fp3</code> written in hexadecimal format.  As a GNU extension, GCC
supports this in C90 mode (except in some cases when strictly
conforming) and in C++.  In that format the
&lsquo;<samp><span class="samp">0x</span></samp>&rsquo; hex introducer and the &lsquo;<samp><span class="samp">p</span></samp>&rsquo; or &lsquo;<samp><span class="samp">P</span></samp>&rsquo; exponent field are
mandatory.  The exponent is a decimal number that indicates the power of
2 by which the significant part will be multiplied.  Thus &lsquo;<samp><span class="samp">0x1.f</span></samp>&rsquo; is
1 15/16,
&lsquo;<samp><span class="samp">p3</span></samp>&rsquo; multiplies it by 8, and the value of <code>0x1.fp3</code>
is the same as <code>1.55e1</code>.

 <p>Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation.  Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., <code>0x1.f</code>.  This
could mean <code>1.0f</code> or <code>1.9375</code> since &lsquo;<samp><span class="samp">f</span></samp>&rsquo; is also the
extension for floating-point constants of type <code>float</code>.

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