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1 | <html> |
| 2 | <head> | |
| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>Internal Floating-point Promotion Policies</title> | |
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| 8 | <link rel="up" href="../pol_ref.html" title="Policy Reference"> | |
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| 21 | <hr> | |
| 22 | <div class="spirit-nav"> | |
| 23 | <a accesskey="p" href="error_handling_policies.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../pol_ref.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="assert_undefined.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h3 class="title"> | |
| 27 | <a name="math_toolkit.pol_ref.internal_promotion"></a><a class="link" href="internal_promotion.html" title="Internal Floating-point Promotion Policies">Internal Floating-point | |
| 28 | Promotion Policies</a> | |
| 29 | </h3></div></div></div> | |
| 30 | <p> | |
| 31 | Normally when evaluating a function at say <code class="computeroutput"><span class="keyword">float</span></code> | |
| 32 | precision, maximal accuracy is assured by conducting the calculation at | |
| 33 | <code class="computeroutput"><span class="keyword">double</span></code> precision internally, | |
| 34 | and then rounding the result. There are two policies that control whether | |
| 35 | internal promotion to a higher precision floating-point type takes place, | |
| 36 | or not: | |
| 37 | </p> | |
| 38 | <div class="informaltable"><table class="table"> | |
| 39 | <colgroup> | |
| 40 | <col> | |
| 41 | <col> | |
| 42 | </colgroup> | |
| 43 | <thead><tr> | |
| 44 | <th> | |
| 45 | <p> | |
| 46 | Policy | |
| 47 | </p> | |
| 48 | </th> | |
| 49 | <th> | |
| 50 | <p> | |
| 51 | Meaning | |
| 52 | </p> | |
| 53 | </th> | |
| 54 | </tr></thead> | |
| 55 | <tbody> | |
| 56 | <tr> | |
| 57 | <td> | |
| 58 | <p> | |
| 59 | <code class="computeroutput"><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">promote_float</span><span class="special"><</span><span class="identifier">B</span><span class="special">></span></code> | |
| 60 | </p> | |
| 61 | </td> | |
| 62 | <td> | |
| 63 | <p> | |
| 64 | Indicates whether <code class="computeroutput"><span class="keyword">float</span></code> | |
| 65 | arguments should be promoted to <code class="computeroutput"><span class="keyword">double</span></code> | |
| 66 | precision internally: defaults 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">policies</span><span class="special">::</span><span class="identifier">promote_float</span><span class="special"><</span><span class="keyword">true</span><span class="special">></span></code> | |
| 67 | </p> | |
| 68 | </td> | |
| 69 | </tr> | |
| 70 | <tr> | |
| 71 | <td> | |
| 72 | <p> | |
| 73 | <code class="computeroutput"><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">promote_double</span><span class="special"><</span><span class="identifier">B</span><span class="special">></span></code> | |
| 74 | </p> | |
| 75 | </td> | |
| 76 | <td> | |
| 77 | <p> | |
| 78 | Indicates whether <code class="computeroutput"><span class="keyword">double</span></code> | |
| 79 | arguments should be promoted to <code class="computeroutput"><span class="keyword">long</span> | |
| 80 | <span class="keyword">double</span></code> precision internally: | |
| 81 | defaults 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">policies</span><span class="special">::</span><span class="identifier">promote_double</span><span class="special"><</span><span class="keyword">true</span><span class="special">></span></code> | |
| 82 | </p> | |
| 83 | </td> | |
| 84 | </tr> | |
| 85 | </tbody> | |
| 86 | </table></div> | |
| 87 | <h5> | |
| 88 | <a name="math_toolkit.pol_ref.internal_promotion.h0"></a> | |
| 89 | <span class="phrase"><a name="math_toolkit.pol_ref.internal_promotion.examples"></a></span><a class="link" href="internal_promotion.html#math_toolkit.pol_ref.internal_promotion.examples">Examples</a> | |
| 90 | </h5> | |
| 91 | <p> | |
| 92 | Suppose we want <code class="computeroutput"><span class="identifier">tgamma</span></code> to | |
| 93 | be evaluated without internal promotion to <code class="computeroutput"><span class="keyword">long</span> | |
| 94 | <span class="keyword">double</span></code>, then we could use: | |
| 95 | </p> | |
| 96 | <pre class="programlisting"><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">special_functions</span><span class="special">/</span><span class="identifier">gamma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> | |
| 97 | ||
| 98 | <span class="keyword">using</span> <span class="keyword">namespace</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> | |
| 99 | <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">;</span> | |
| 100 | ||
| 101 | <span class="comment">// Define a new policy *not* internally promoting RealType to double:</span> | |
| 102 | <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span> | |
| 103 | <span class="identifier">promote_double</span><span class="special"><</span><span class="keyword">false</span><span class="special">></span> | |
| 104 | <span class="special">></span> <span class="identifier">my_policy</span><span class="special">;</span> | |
| 105 | ||
| 106 | <span class="comment">// Call the function, applying the new policy:</span> | |
| 107 | <span class="keyword">double</span> <span class="identifier">t1</span> <span class="special">=</span> <span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">some_value</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">());</span> | |
| 108 | ||
| 109 | <span class="comment">// Alternatively we could use helper function make_policy,</span> | |
| 110 | <span class="comment">// and concisely define everything at the call site:</span> | |
| 111 | <span class="keyword">double</span> <span class="identifier">t2</span> <span class="special">=</span> <span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">some_value</span><span class="special">,</span> <span class="identifier">make_policy</span><span class="special">(</span><span class="identifier">promote_double</span><span class="special"><</span><span class="keyword">false</span><span class="special">>()));</span> | |
| 112 | </pre> | |
| 113 | <p> | |
| 114 | Alternatively, suppose we want a distribution to perform calculations without | |
| 115 | promoting <code class="computeroutput"><span class="keyword">float</span></code> to <code class="computeroutput"><span class="keyword">double</span></code>, then we could use: | |
| 116 | </p> | |
| 117 | <pre class="programlisting"><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">distributions</span><span class="special">/</span><span class="identifier">normal</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> | |
| 118 | <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">normal_distribution</span><span class="special">;</span> | |
| 119 | ||
| 120 | <span class="keyword">using</span> <span class="keyword">namespace</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> | |
| 121 | ||
| 122 | <span class="comment">// Define a policy:</span> | |
| 123 | <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span> | |
| 124 | <span class="identifier">promote_float</span><span class="special"><</span><span class="keyword">false</span><span class="special">></span> | |
| 125 | <span class="special">></span> <span class="identifier">my_policy</span><span class="special">;</span> | |
| 126 | ||
| 127 | <span class="comment">// Define the new normal distribution using my_policy:</span> | |
| 128 | <span class="keyword">typedef</span> <span class="identifier">normal_distribution</span><span class="special"><</span><span class="keyword">float</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></span> <span class="identifier">my_norm</span><span class="special">;</span> | |
| 129 | ||
| 130 | <span class="comment">// Get a quantile:</span> | |
| 131 | <span class="keyword">float</span> <span class="identifier">q</span> <span class="special">=</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">my_norm</span><span class="special">(),</span> <span class="number">0.05f</span><span class="special">);</span> | |
| 132 | </pre> | |
| 133 | </div> | |
| 134 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 135 | <td align="left"></td> | |
| 136 | <td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal, | |
| 137 | Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert | |
| 138 | Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan Råde, Gautam Sewani, | |
| 139 | Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p> | |
| 140 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 141 | 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>) | |
| 142 | </p> | |
| 143 | </div></td> | |
| 144 | </tr></table> | |
| 145 | <hr> | |
| 146 | <div class="spirit-nav"> | |
| 147 | <a accesskey="p" href="error_handling_policies.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../pol_ref.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="assert_undefined.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 148 | </div> | |
| 149 | </body> | |
| 150 | </html> |