libs/math/doc/html/math_toolkit/greatest_typdefs.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Greatest-width floating-point typedef</title>
   5 <link rel="stylesheet" href="../math.css" type="text/css">
   6 <meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
   7 <link rel="home" href="../index.html" title="Math Toolkit 2.5.2">
   8 <link rel="up" href="../cstdfloat.html" title="Chapter&#160;3.&#160;Specified-width floating-point typedefs">
   9 <link rel="prev" href="fastest_typdefs.html" title="Fastest floating-point typedefs">
  10 <link rel="next" href="macros.html" title="Floating-Point Constant Macros">
  11 </head>
  12 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  13 <table cellpadding="2" width="100%"><tr>
  14 <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
  15 <td align="center"><a href="../../../../../index.html">Home</a></td>
  16 <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
  17 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  19 <td align="center"><a href="../../../../../more/index.htm">More</a></td>
  20 </tr></table>
  21 <hr>
  22 <div class="spirit-nav">
  23 <a accesskey="p" href="fastest_typdefs.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="macros.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="math_toolkit.greatest_typdefs"></a><a class="link" href="greatest_typdefs.html" title="Greatest-width floating-point typedef">Greatest-width floating-point
  28     typedef</a>
  29 </h2></div></div></div>
  30 <p>
  31       The <code class="computeroutput"><span class="keyword">typedef</span> <span class="identifier">floatmax_t</span></code>
  32       designates a floating-point type capable of representing any value of any floating-point
  33       type in a given platform most precisely.
  34     </p>
  35 <p>
  36       The greatest-width <code class="computeroutput"><span class="keyword">typedef</span></code> is
  37       provided for all platforms, but, of course, the size may vary.
  38     </p>
  39 <p>
  40       To provide floating-point <span class="bold"><strong>constants</strong></span> most precisely
  41       representable for a <code class="computeroutput"><span class="identifier">floatmax_t</span></code>
  42       type, use the macro <code class="computeroutput"><span class="identifier">BOOST_FLOATMAX_C</span></code>.
  43     </p>
  44 <p>
  45       For example, replace a constant <code class="computeroutput"><span class="number">123.4567890123456789012345678901234567890</span></code>
  46       with
  47     </p>
  48 <pre class="programlisting"><span class="identifier">BOOST_FLOATMAX_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span>
  49 </pre>
  50 <p>
  51       If, for example, <code class="computeroutput"><span class="identifier">floatmax_t</span></code>
  52       is <code class="computeroutput"><span class="identifier">float64_t</span></code> then the result
  53       will be equivalent to a <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">double</span></code> suffixed with L, but if <code class="computeroutput"><span class="identifier">floatmax_t</span></code> is <code class="computeroutput"><span class="identifier">float128_t</span></code>
  54       then the result will be equivalent to a <code class="computeroutput"><span class="identifier">quad</span>
  55       <span class="identifier">type</span></code> suffixed with Q (assuming, of
  56       course, that <code class="computeroutput"><span class="identifier">float128_t</span></code> (<code class="computeroutput"><span class="identifier">__float128</span></code> or <code class="computeroutput"><span class="identifier">Quad</span></code>)
  57       is supported).
  58     </p>
  59 <p>
  60       If we display with <code class="computeroutput"><span class="identifier">max_digits10</span></code>,
  61       the maximum possibly significant decimal digits:
  62     </p>
  63 <pre class="programlisting"><span class="preprocessor">#ifdef</span> <span class="identifier">BOOST_FLOAT32_C</span>
  64   <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">.</span><span class="identifier">precision</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">max_digits10</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">float32_t</span><span class="special">&gt;());</span> <span class="comment">// Show all significant decimal digits,</span>
  65   <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">.</span><span class="identifier">setf</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios</span><span class="special">::</span><span class="identifier">showpoint</span><span class="special">);</span> <span class="comment">// including all significant trailing zeros.</span>
  66   <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"BOOST_FLOAT32_C(123.4567890123456789012345678901234567890) = "</span>
  67     <span class="special">&lt;&lt;</span> <span class="identifier">BOOST_FLOAT32_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
  68   <span class="comment">//   BOOST_FLOAT32_C(123.4567890123456789012345678901234567890) = 123.456787</span>
  69 <span class="preprocessor">#endif</span>
  70 </pre>
  71 <p>
  72       then on a 128-bit platform (GCC 4.8.1 or higher with quadmath):
  73     </p>
  74 <pre class="programlisting"><span class="identifier">BOOST_FLOAT32_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.456787</span>
  75 <span class="identifier">BOOST_FLOAT64_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.45678901234568</span>
  76 <span class="identifier">BOOST_FLOAT80_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.456789012345678903</span>
  77 <span class="identifier">BOOST_FLOAT128_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.456789012345678901234567890123453</span>
  78 </pre>
  79 </div>
  80 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
  81 <td align="left"></td>
  82 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2010, 2012-2014 Nikhar Agrawal,
  83       Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
  84       Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan R&#229;de, Gautam Sewani,
  85       Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p>
  86         Distributed under the Boost Software License, Version 1.0. (See accompanying
  87         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>)
  88       </p>
  89 </div></td>
  90 </tr></table>
  91 <hr>
  92 <div class="spirit-nav">
  93 <a accesskey="p" href="fastest_typdefs.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="macros.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
  94 </div>
  95 </body>
  96 </html>