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| <h3 class="section">6.14 Hex Floats</h3> |
| <a name="index-hex-floats"></a> |
| |
| <p>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>0x</samp>’ hex introducer and the ‘<samp>p</samp>’ or ‘<samp>P</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>0x1.f</samp>’ is |
| 1 15/16, |
| ‘<samp>p3</samp>’ multiplies it by 8, and the value of <code>0x1.fp3</code> |
| is the same as <code>1.55e1</code>. |
| </p> |
| <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>f</samp>’ is also the |
| extension for floating-point constants of type <code>float</code>. |
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