1<html lang="en"> 2<head> 3<title>Hex Floats - Using the GNU Compiler Collection (GCC)</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Using the GNU Compiler Collection (GCC)"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions"> 9<link rel="prev" href="Decimal-Float.html#Decimal-Float" title="Decimal Float"> 10<link rel="next" href="Fixed_002dPoint.html#Fixed_002dPoint" title="Fixed-Point"> 11<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 12<!-- 13Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 141998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 152010 Free Software Foundation, Inc. 16 17Permission is granted to copy, distribute and/or modify this document 18under the terms of the GNU Free Documentation License, Version 1.3 or 19any later version published by the Free Software Foundation; with the 20Invariant Sections being ``Funding Free Software'', the Front-Cover 21Texts being (a) (see below), and with the Back-Cover Texts being (b) 22(see below). A copy of the license is included in the section entitled 23``GNU Free Documentation License''. 24 25(a) The FSF's Front-Cover Text is: 26 27 A GNU Manual 28 29(b) The FSF's Back-Cover Text is: 30 31 You have freedom to copy and modify this GNU Manual, like GNU 32 software. Copies published by the Free Software Foundation raise 33 funds for GNU development.--> 34<meta http-equiv="Content-Style-Type" content="text/css"> 35<style type="text/css"><!-- 36 pre.display { font-family:inherit } 37 pre.format { font-family:inherit } 38 pre.smalldisplay { font-family:inherit; font-size:smaller } 39 pre.smallformat { font-family:inherit; font-size:smaller } 40 pre.smallexample { font-size:smaller } 41 pre.smalllisp { font-size:smaller } 42 span.sc { font-variant:small-caps } 43 span.roman { font-family:serif; font-weight:normal; } 44 span.sansserif { font-family:sans-serif; font-weight:normal; } 45--></style> 46<link rel="stylesheet" type="text/css" href="../cs.css"> 47</head> 48<body> 49<div class="node"> 50<a name="Hex-Floats"></a> 51<p> 52Next: <a rel="next" accesskey="n" href="Fixed_002dPoint.html#Fixed_002dPoint">Fixed-Point</a>, 53Previous: <a rel="previous" accesskey="p" href="Decimal-Float.html#Decimal-Float">Decimal Float</a>, 54Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a> 55<hr> 56</div> 57 58<h3 class="section">6.14 Hex Floats</h3> 59 60<p><a name="index-hex-floats-2306"></a> 61ISO C99 supports floating-point numbers written not only in the usual 62decimal notation, such as <code>1.55e1</code>, but also numbers such as 63<code>0x1.fp3</code> written in hexadecimal format. As a GNU extension, GCC 64supports this in C90 mode (except in some cases when strictly 65conforming) and in C++. In that format the 66‘<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 67mandatory. The exponent is a decimal number that indicates the power of 682 by which the significant part will be multiplied. Thus ‘<samp><span class="samp">0x1.f</span></samp>’ is 691 15/16, 70‘<samp><span class="samp">p3</span></samp>’ multiplies it by 8, and the value of <code>0x1.fp3</code> 71is the same as <code>1.55e1</code>. 72 73 <p>Unlike for floating-point numbers in the decimal notation the exponent 74is always required in the hexadecimal notation. Otherwise the compiler 75would not be able to resolve the ambiguity of, e.g., <code>0x1.f</code>. This 76could mean <code>1.0f</code> or <code>1.9375</code> since ‘<samp><span class="samp">f</span></samp>’ is also the 77extension for floating-point constants of type <code>float</code>. 78 79 </body></html> 80 81