109 lines
6.8 KiB
HTML
109 lines
6.8 KiB
HTML
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
|
|
<title>Hints on using float128 (and __float128)</title>
|
|
<link rel="stylesheet" href="../math.css" type="text/css">
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
|
|
<link rel="home" href="../index.html" title="Math Toolkit 2.11.0">
|
|
<link rel="up" href="../cstdfloat.html" title="Chapter 3. Specified-width floating-point typedefs">
|
|
<link rel="prev" href="examples.html" title="Examples">
|
|
<link rel="next" href="float128.html" title="Implementation of Float128 type">
|
|
</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="examples.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="float128.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.float128_hints"></a><a class="link" href="float128_hints.html" title="Hints on using float128 (and __float128)">Hints on using float128 (and
|
|
__float128)</a>
|
|
</h2></div></div></div>
|
|
<h6>
|
|
<a name="math_toolkit.float128_hints.h0"></a>
|
|
<span class="phrase"><a name="math_toolkit.float128_hints.different_float128"></a></span><a class="link" href="float128_hints.html#math_toolkit.float128_hints.different_float128">__float128
|
|
versus float128</a>
|
|
</h6>
|
|
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
|
|
<li class="listitem">
|
|
__float128 is the (optionally) compiler supplied hardware type, it's an
|
|
C-ish extension to C++ and there is only minimal support for it in normal
|
|
C++ (no IO streams or <code class="computeroutput"><span class="identifier">numeric_limits</span></code>
|
|
support, function names in libquadmath all have different names to the
|
|
<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span></code>
|
|
ones etc.) So you can program type <code class="computeroutput"><span class="identifier">__float128</span></code>
|
|
directly, but it's harder work.
|
|
</li>
|
|
<li class="listitem">
|
|
Type <code class="computeroutput"><span class="identifier">float128</span></code> uses __float128
|
|
and makes it C++ and generic code friendly, with all the usual standard
|
|
<code class="computeroutput"><span class="identifier">iostream</span></code>, <code class="computeroutput"><span class="identifier">numeric_limits</span></code>, <code class="computeroutput"><span class="identifier">complex</span></code>
|
|
in namspace <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span></code>
|
|
available, so strongly recommended for C++ use.
|
|
</li>
|
|
</ul></div>
|
|
<h6>
|
|
<a name="math_toolkit.float128_hints.h1"></a>
|
|
<span class="phrase"><a name="math_toolkit.float128_hints.hints_and_tips"></a></span><a class="link" href="float128_hints.html#math_toolkit.float128_hints.hints_and_tips">Hints
|
|
and tips</a>
|
|
</h6>
|
|
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
|
|
<li class="listitem">
|
|
Make sure you declare variables with the correct type, here <code class="computeroutput"><span class="identifier">float128</span></code>.
|
|
</li>
|
|
<li class="listitem">
|
|
Make sure that if you pass a variable to a function then it is casted to
|
|
<code class="computeroutput"><span class="identifier">float128</span></code>.
|
|
</li>
|
|
<li class="listitem">
|
|
Make sure you declare literals with the correct suffix - otherwise they'll
|
|
be treated as type <code class="computeroutput"><span class="keyword">double</span></code>
|
|
with catastrophic loss of precision. So make sure they have a Q suffix
|
|
for 128-bit floating-point literals.
|
|
</li>
|
|
<li class="listitem">
|
|
All the std library functions, cmath functions, plus all the constants,
|
|
and special functions from Boost.Math should then just work.
|
|
</li>
|
|
<li class="listitem">
|
|
Make sure std lib functions are called <span class="bold"><strong>unqualified</strong></span>
|
|
so that the correct overload is found via <a href="http://en.cppreference.com/w/cpp/language/adl" target="_top">Argument
|
|
Dependent Lookup (ADL)</a>. So write sqrt(variable) and not std::sqrt(variable).
|
|
</li>
|
|
<li class="listitem">
|
|
In general, try not to reinvent stuff - using constants from Boost.Math
|
|
is probably less error prone than declaring your own, likewise the special
|
|
functions etc.
|
|
</li>
|
|
</ul></div>
|
|
<p>
|
|
Some examples of what can go horribly and silently wrong are at <a href="../../../example/float128_example.cpp" target="_top">float128_example.cpp</a>.
|
|
</p>
|
|
</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 © 2006-2019 Nikhar
|
|
Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos,
|
|
Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan
|
|
Råde, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg,
|
|
Daryle Walker and Xiaogang Zhang<p>
|
|
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>)
|
|
</p>
|
|
</div></td>
|
|
</tr></table>
|
|
<hr>
|
|
<div class="spirit-nav">
|
|
<a accesskey="p" href="examples.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="float128.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
|
|
</div>
|
|
</body>
|
|
</html>
|