268 lines
32 KiB
HTML
268 lines
32 KiB
HTML
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
|
|
<title>Defining New Constants</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="../constants.html" title="Chapter 4. Mathematical Constants">
|
|
<link rel="prev" href="constants.html" title="The Mathematical Constants">
|
|
<link rel="next" href="constants_faq.html" title="Math Constants FAQs">
|
|
</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="constants.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../constants.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="constants_faq.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.new_const"></a><a class="link" href="new_const.html" title="Defining New Constants">Defining New Constants</a>
|
|
</h2></div></div></div>
|
|
<p>
|
|
The library provides some helper code to assist in defining new constants;
|
|
the process for defining a constant called <code class="computeroutput"><span class="identifier">my_constant</span></code>
|
|
goes like this:
|
|
</p>
|
|
<p>
|
|
1. <span class="bold"><strong>Define a function that calculates the value of the
|
|
constant</strong></span>. This should be a template function, and be placed in
|
|
<code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">calculate_constants</span><span class="special">.</span><span class="identifier">hpp</span></code> if the
|
|
constant is to be added to this library, or else defined at the top of your
|
|
source file if not.
|
|
</p>
|
|
<p>
|
|
The function should look like this:
|
|
</p>
|
|
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">constants</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">detail</span><span class="special">{</span>
|
|
|
|
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Real</span><span class="special">></span>
|
|
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span>
|
|
<span class="identifier">Real</span> <span class="identifier">constant_my_constant</span><span class="special"><</span><span class="identifier">Real</span><span class="special">>::</span><span class="identifier">compute</span><span class="special">(</span><span class="identifier">BOOST_MATH_EXPLICIT_TEMPLATE_TYPE_SPEC</span><span class="special">(</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">N</span><span class="special">>))</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">int</span> <span class="identifier">required_precision</span> <span class="special">=</span> <span class="identifier">N</span> <span class="special">?</span> <span class="identifier">N</span> <span class="special">:</span> <span class="identifier">tools</span><span class="special">::</span><span class="identifier">digits</span><span class="special"><</span><span class="identifier">Real</span><span class="special">>();</span>
|
|
<span class="identifier">Real</span> <span class="identifier">result</span> <span class="special">=</span> <span class="comment">/* value computed to required_precision bits */</span> <span class="special">;</span>
|
|
<span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
|
|
<span class="special">}}}}</span> <span class="comment">// namespaces</span>
|
|
</pre>
|
|
<p>
|
|
Then define a placeholder for the constant itself:
|
|
</p>
|
|
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">constants</span><span class="special">{</span>
|
|
|
|
<span class="identifier">BOOST_DEFINE_MATH_CONSTANT</span><span class="special">(</span><span class="identifier">my_constant</span><span class="special">,</span> <span class="number">0.0</span><span class="special">,</span> <span class="string">"0"</span><span class="special">);</span>
|
|
|
|
<span class="special">}}}</span>
|
|
</pre>
|
|
<p>
|
|
For example, to calculate π/2, add to <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">calculate_constants</span><span class="special">.</span><span class="identifier">hpp</span></code>
|
|
</p>
|
|
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
|
|
<span class="keyword">template</span><span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span>
|
|
<span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">constant_half_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">compute</span><span class="special">(</span><span class="identifier">BOOST_MATH_EXPLICIT_TEMPLATE_TYPE_SPEC</span><span class="special">(</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">N</span><span class="special">>))</span>
|
|
<span class="special">{</span>
|
|
<span class="identifier">BOOST_MATH_STD_USING</span>
|
|
<span class="keyword">return</span> <span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special"><</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">digits2</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">></span> <span class="special">>()</span> <span class="special">/</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="number">2</span><span class="special">);</span>
|
|
<span class="special">}</span>
|
|
</pre>
|
|
<p>
|
|
Then to <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">constants</span><span class="special">.</span><span class="identifier">hpp</span></code> add:
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">BOOST_DEFINE_MATH_CONSTANT</span><span class="special">(</span><span class="identifier">half_pi</span><span class="special">,</span> <span class="number">0.0</span><span class="special">,</span> <span class="string">"0"</span><span class="special">);</span> <span class="comment">// Actual values are temporary, we'll replace them later.</span>
|
|
</pre>
|
|
<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"><p>
|
|
Previously defined constants like pi and e can be used, but by <span class="bold"><strong>not simply calling</strong></span> <code class="computeroutput"><span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span></code>;
|
|
specifying the precision via the policy <code class="computeroutput"><span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span>
|
|
<span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special"><</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">digits2</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">></span> <span class="special">>()</span></code>
|
|
is essential to ensure full accuracy.
|
|
</p></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">
|
|
<p>
|
|
Newly defined constants can only be used once they are included in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">constants</span><span class="special">.</span><span class="identifier">hpp</span></code>. So
|
|
if you add <code class="computeroutput"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">N</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">constant_my_constant</span><span class="special">{...}</span></code>,
|
|
then you cannot define <code class="computeroutput"><span class="identifier">constant_my_constant</span></code>
|
|
until you add the temporary <code class="computeroutput"><span class="identifier">BOOST_DEFINE_MATH_CONSTANT</span><span class="special">(</span><span class="identifier">my_constant</span><span class="special">,</span> <span class="number">0.0</span><span class="special">,</span>
|
|
<span class="string">"0"</span><span class="special">)</span></code>.
|
|
Failing to do this will result in surprising compile errors:
|
|
</p>
|
|
<pre class="programlisting"><span class="identifier">error</span> <span class="identifier">C2143</span><span class="special">:</span> <span class="identifier">syntax</span> <span class="identifier">error</span> <span class="special">:</span> <span class="identifier">missing</span> <span class="char">';'</span> <span class="identifier">before</span> <span class="char">'<'</span>
|
|
<span class="identifier">error</span> <span class="identifier">C2433</span><span class="special">:</span> <span class="char">'constant_root_two_div_pi'</span> <span class="special">:</span> <span class="char">'inline'</span> <span class="keyword">not</span> <span class="identifier">permitted</span> <span class="identifier">on</span> <span class="identifier">data</span> <span class="identifier">declarations</span>
|
|
<span class="identifier">error</span> <span class="identifier">C2888</span><span class="special">:</span> <span class="char">'T constant_root_two_div_pi'</span> <span class="special">:</span> <span class="identifier">symbol</span> <span class="identifier">cannot</span> <span class="identifier">be</span> <span class="identifier">defined</span> <span class="identifier">within</span> <span class="keyword">namespace</span> <span class="char">'detail'</span>
|
|
<span class="identifier">error</span> <span class="identifier">C2988</span><span class="special">:</span> <span class="identifier">unrecognizable</span> <span class="keyword">template</span> <span class="identifier">declaration</span><span class="special">/</span><span class="identifier">definition</span>
|
|
</pre>
|
|
</td></tr>
|
|
</table></div>
|
|
<p>
|
|
2. <span class="bold"><strong>You will need an arbitrary precision type to use to
|
|
calculate the value</strong></span>. This library currently supports either <code class="computeroutput"><span class="identifier">cpp_float</span></code>, <code class="computeroutput"><span class="identifier">NTL</span><span class="special">::</span><span class="identifier">RR</span></code> or
|
|
<code class="computeroutput"><span class="identifier">mpfr_class</span></code> used via the bindings
|
|
in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">bindings</span></code>.
|
|
The default is to use <code class="computeroutput"><span class="identifier">NTL</span><span class="special">::</span><span class="identifier">RR</span></code> unless you define an alternate macro,
|
|
for example, <code class="computeroutput"><span class="identifier">USE_MPFR</span></code> or <code class="computeroutput"><span class="identifier">USE_CPP_FLOAT</span></code> at the start of your program.
|
|
</p>
|
|
<p>
|
|
3. It is necessary to link to the Boost.Regex library, and probably to your
|
|
chosen arbitrary precision type library.
|
|
</p>
|
|
<p>
|
|
4. You need to add <code class="computeroutput"><span class="identifier">libs</span><span class="special">\</span><span class="identifier">math</span><span class="special">\</span><span class="identifier">include_private</span></code>
|
|
to your compiler's include path as the needed header is not installed in the
|
|
usual places by default (this avoids a cyclic dependency between the Math and
|
|
Multiprecision library's headers).
|
|
</p>
|
|
<p>
|
|
5. The complete program to generate the constant <code class="computeroutput"><span class="identifier">half_pi</span></code>
|
|
using function <code class="computeroutput"><span class="identifier">calculate_half_pi</span></code>
|
|
is then:
|
|
</p>
|
|
<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">USE_CPP_FLOAT</span> <span class="comment">// If required.</span>
|
|
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">generate</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
|
|
|
|
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
|
|
<span class="special">{</span>
|
|
<span class="identifier">BOOST_CONSTANTS_GENERATE</span><span class="special">(</span><span class="identifier">half_pi</span><span class="special">);</span>
|
|
<span class="special">}</span>
|
|
</pre>
|
|
<p>
|
|
The output from the program is a snippet of C++ code (actually a macro call)
|
|
that can be cut and pasted into <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">constants</span><span class="special">.</span><span class="identifier">hpp</span></code> or else into your own code, for example:
|
|
</p>
|
|
<pre class="programlisting"> BOOST_DEFINE_MATH_CONSTANT(half_pi, 1.570796326794896619231321691639751442e+00, "1.57079632679489661923132169163975144209858469968755291048747229615390820314310449931401741267105853399107404326e+00");
|
|
</pre>
|
|
<p>
|
|
This macro BOOST_DEFINE_MATH_CONSTANT inserts a C++ struct code snippet that
|
|
declares the <code class="computeroutput"><span class="keyword">float</span></code>, <code class="computeroutput"><span class="keyword">double</span></code> and <code class="computeroutput"><span class="keyword">long</span>
|
|
<span class="keyword">double</span></code> versions of the constant, plus
|
|
a decimal digit string representation correct to 100 decimal digits, and all
|
|
the meta-programming machinery needed to select between them.
|
|
</p>
|
|
<p>
|
|
The result of an expanded macro for Pi is shown below.
|
|
</p>
|
|
<pre class="programlisting"><span class="comment">// Preprocessed pi constant, annotated.</span>
|
|
|
|
<span class="keyword">namespace</span> <span class="identifier">boost</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">namespace</span> <span class="identifier">math</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">namespace</span> <span class="identifier">constants</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">namespace</span> <span class="identifier">detail</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">constant_pi</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">private</span><span class="special">:</span>
|
|
<span class="comment">// Default implementations from string of decimal digits:</span>
|
|
<span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get_from_string</span><span class="special">()</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="identifier">result</span>
|
|
<span class="special">=</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">convert_from_string</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="string">"3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651e+00"</span><span class="special">,</span>
|
|
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_convertible</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*,</span> <span class="identifier">T</span><span class="special">>());</span>
|
|
<span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span> <span class="keyword">static</span> <span class="identifier">T</span> <span class="identifier">compute</span><span class="special">();</span>
|
|
|
|
<span class="keyword">public</span><span class="special">:</span>
|
|
<span class="comment">// Default implementations from string of decimal digits:</span>
|
|
<span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">construct_from_string</span><span class="special">>&)</span>
|
|
<span class="special">{</span>
|
|
<span class="identifier">constant_initializer</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="special">&</span> <span class="identifier">constant_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get_from_string</span> <span class="special">>::</span><span class="identifier">do_nothing</span><span class="special">();</span>
|
|
<span class="keyword">return</span> <span class="identifier">get_from_string</span><span class="special">();</span>
|
|
<span class="special">}</span>
|
|
<span class="comment">// Float, double and long double versions:</span>
|
|
<span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">construct_from_float</span><span class="special">>)</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">return</span> <span class="number">3.141592653589793238462643383279502884e+00F</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
<span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">construct_from_double</span><span class="special">>&)</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">return</span> <span class="number">3.141592653589793238462643383279502884e+00</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
<span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">construct_from_long_double</span><span class="special">>&)</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">return</span> <span class="number">3.141592653589793238462643383279502884e+00L</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
<span class="comment">// For very high precision that is nonetheless can be calculated at compile time:</span>
|
|
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span> <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">N</span><span class="special">>&</span> <span class="identifier">n</span><span class="special">)</span>
|
|
<span class="special">{</span>
|
|
<span class="identifier">constant_initializer2</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">,</span> <span class="special">&</span> <span class="identifier">constant_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">template</span> <span class="identifier">compute</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">>::</span><span class="identifier">do_nothing</span><span class="special">();</span>
|
|
<span class="keyword">return</span> <span class="identifier">compute</span><span class="special"><</span><span class="identifier">N</span><span class="special">>();</span>
|
|
<span class="special">}</span>
|
|
<span class="comment">//For true arbitrary precision, which may well vary at runtime.</span>
|
|
<span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="number">0</span><span class="special">>&)</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">return</span> <span class="identifier">tools</span><span class="special">::</span><span class="identifier">digits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span> <span class="special">></span> <span class="identifier">max_string_digits</span> <span class="special">?</span> <span class="identifier">compute</span><span class="special"><</span><span class="number">0</span><span class="special">>()</span> <span class="special">:</span> <span class="identifier">get</span><span class="special">(</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">int_</span><span class="special"><</span><span class="identifier">construct_from_string</span><span class="special">>());</span>
|
|
<span class="special">}</span>
|
|
<span class="special">};</span> <span class="comment">// template <class T> struct constant_pi</span>
|
|
<span class="special">}</span> <span class="comment">// namespace detail</span>
|
|
|
|
<span class="comment">// The actual forwarding function (including policy to control precision).</span>
|
|
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Policy</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">pi</span><span class="special">(</span> <span class="special">)</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">return</span> <span class="identifier">detail</span><span class="special">::</span> <span class="identifier">constant_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get</span><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">construction_traits</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Policy</span><span class="special">>::</span><span class="identifier">type</span><span class="special">());</span>
|
|
<span class="special">}</span>
|
|
<span class="comment">// The actual forwarding function (using default policy to control precision).</span>
|
|
<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">pi</span><span class="special">()</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">return</span> <span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special"><></span> <span class="special">>()</span>
|
|
<span class="special">}</span>
|
|
<span class="special">}</span> <span class="comment">// namespace constants</span>
|
|
|
|
<span class="comment">// Namespace specific versions, for the three built-in floats:</span>
|
|
<span class="keyword">namespace</span> <span class="identifier">float_constants</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">float</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="number">3.141592653589793238462643383279502884e+00F</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
<span class="keyword">namespace</span> <span class="identifier">double_constants</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="number">3.141592653589793238462643383279502884e+00</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
<span class="keyword">namespace</span> <span class="identifier">long_double_constants</span>
|
|
<span class="special">{</span>
|
|
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">long</span> <span class="keyword">double</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="number">3.141592653589793238462643383279502884e+00L</span><span class="special">;</span>
|
|
<span class="special">}</span>
|
|
<span class="keyword">namespace</span> <span class="identifier">constants</span><span class="special">{;</span>
|
|
<span class="special">}</span> <span class="comment">// namespace constants</span>
|
|
<span class="special">}</span> <span class="comment">// namespace math</span>
|
|
<span class="special">}</span> <span class="comment">// namespace boost</span>
|
|
</pre>
|
|
</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="constants.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../constants.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="constants_faq.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
|
|
</div>
|
|
</body>
|
|
</html>
|