boost-react-native-bundle

<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Rationale</title> <link rel="stylesheet" href="../math.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../index.html" title="Math Toolkit 2.1.0"> <link rel="up" href="../cstdfloat.html" title="Chapter 3. Specified-width floating-point typedefs"> <link rel="prev" href="overview.html" title="Overview"> <link rel="next" href="exact_typdefs.html" title="Exact-Width Floating-Point typedefs"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> <td align="center"><a href="../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="overview.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../cstdfloat.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exact_typdefs.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="math_toolkit.rationale"></a><a class="link" href="rationale.html" title="Rationale">Rationale</a> </h2></div></div></div> The implementation of <code class="computeroutput"><boost/cstdfloat.hpp></code> is designed to utilize <code class="computeroutput"><float.h></code>, defined in the 1989 C standard. The preprocessor is used to query certain preprocessor definitions in <code class="computeroutput"><float.h></code> such as FLT_MAX, DBL_MAX, etc. Based on the results of these queries, an attempt is made to automatically detect the presence of built-in floating-point types having specified widths. An unequivocal test regarding conformance with <a href="http://en.wikipedia.org/wiki/IEEE_floating_point" target="_top">IEEE_floating_point</a> (IEC599) based on <a href="http://en.cppreference.com/w/cpp/types/numeric_limits/is_iec559" target="_top"><code class="computeroutput">std::numeric_limits<>::is_iec559</code></a> is performed with <code class="computeroutput">BOOST_STATIC_ASSERT</code>. In addition, this Boost implementation <code class="computeroutput"><boost/cstdfloat.hpp></code> supports an 80-bit floating-point <code class="computeroutput">typedef</code> if it can be detected, and a 128-bit floating-point <code class="computeroutput">typedef</code> if it can be detected, provided that the underlying types conform with <a href="http://en.wikipedia.org/wiki/Extended_precision" target="_top">IEEE-754 precision extension</a> (if<code class="computeroutput">std::numeric_limits<>::is_iec559</code> is true for this type). The header <code class="computeroutput"><boost/cstdfloat.hpp></code> makes the standardized floating-point <code class="computeroutput">typedef</code>s safely available in <code class="computeroutput">namespace boost</code> without placing any names in <code class="computeroutput">namespace std</code>. The intention is to complement rather than compete with a potential future C/C++ Standard Library that may contain these <code class="computeroutput">typedef</code>s. Should some future C/C++ standard include <code class="computeroutput"><stdfloat.h></code> and <code class="computeroutput"><cstdfloat></code>, then <code class="computeroutput"><boost/cstdfloat.hpp></code> will continue to function, but will become redundant and may be safely deprecated. Because <code class="computeroutput"><boost/cstdfloat.hpp></code> is a Boost header, its name conforms to the boost header naming conventions, not the C++ Standard Library header naming conventions. <div class="note"><table border="0" summary="Note"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> <th align="left">Note</th> </tr> <tr><td align="left" valign="top"> <code class="computeroutput"><boost/cstdfloat.hpp></code> cannot synthesize or create a <code class="computeroutput">typedef</code> if the underlying type is not provided by the compiler. For example, if a compiler does not have an underlying floating-point type with 128 bits (highly sought-after in scientific and numeric programming), then <code class="computeroutput">float128_t</code> and its corresponding least and fast types are not provided by <code class="computeroutput"><boost/cstdfloat.hpp</code>>. </td></tr> </table></div> <div class="warning"><table border="0" summary="Warning"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> <th align="left">Warning</th> </tr> <tr><td align="left" valign="top"> If <code class="computeroutput"><boost/cstdfloat.hpp></code> uses a compiler-specific non-standardized type (not derived from <code class="computeroutput">float, double,</code> or <code class="computeroutput">long double</code>) for one or more of its floating-point <code class="computeroutput">typedef</code>s, then there is no guarantee that specializations of <code class="computeroutput">numeric_limits<></code> will be available for these types. Typically, specializations of <code class="computeroutput">numeric_limits<></code> will only be available for these types if the compiler itself supports corresponding specializations for the underlying type(s), exceptions are GCC's <code class="computeroutput">__float128</code> type and Intel's <code class="computeroutput">_Quad</code> type which are explicitly supported via our own code. </td></tr> </table></div> <div class="warning"><table border="0" summary="Warning"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> <th align="left">Warning</th> </tr> <tr><td align="left" valign="top"> As an implementation artifact, certain C macro names from <code class="computeroutput"><float.h></code> may possibly be visible to users of <code class="computeroutput"><boost/cstdfloat.hpp></code>. Don't rely on using these macros; they are not part of any Boost-specified interface. Use <code class="computeroutput">std::numeric_limits<></code> for floating-point ranges, etc. instead. </td></tr> </table></div> <div class="tip"><table border="0" summary="Tip"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../doc/src/images/tip.png"></td> <th align="left">Tip</th> </tr> <tr><td align="left" valign="top"> For best results, <code class="computeroutput"><boost/cstdfloat.hpp></code> should be <code class="computeroutput">#include</code>d before other headers that define generic code making use of standard library functions defined in <cmath>. This is because <code class="computeroutput"><boost/cstdfloat.hpp></code> may define overloads of standard library functions where a non-standard type (i.e. other than <code class="computeroutput">float</code>, <code class="computeroutput">double</code>, or <code class="computeroutput">long double</code>) is used for one of the specified width types. If generic code (for example in another Boost.Math header) calls a standard library function, then the correct overload will only be found if these overloads are defined prior to the point of use. See implementation for more details. For this reason, making <code class="computeroutput">#include <boost/cstdfloat.hpp></code> the first include is usually best. </td></tr> </table></div> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert Holin, Bruno Lalande, John Maddock, Johan Råde, Gautam Sewani, Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="overview.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../cstdfloat.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exact_typdefs.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>