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<h3 class="section">6.14 Hex Floats</h3>
<p><a name="index-hex-floats-2935"></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
‘<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
mandatory. The exponent is a decimal number that indicates the power of
2 by which the significant part is multiplied. Thus ‘<samp><span class="samp">0x1.f</span></samp>’ is
1 15/16,
‘<samp><span class="samp">p3</span></samp>’ 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 ‘<samp><span class="samp">f</span></samp>’ is also the
extension for floating-point constants of type <code>float</code>.
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