| <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" |
| "http://www.w3.org/TR/html4/loose.dtd"> |
| |
| <html> |
| <head> |
| <meta http-equiv="Content-Language" content="en-us"> |
| <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> |
| <link href="../pool.css" rel="stylesheet" type="text/css"> |
| |
| <title>ct_gcd_lcm - Compile-Time GCD and LCM</title> |
| </head> |
| |
| <body> |
| <img src="../../../../boost.png" width="276" height="86" alt="C++ Boost"> |
| |
| <h1 align="center">ct_gcd_lcm - Compile-Time GCD and LCM</h1> |
| |
| <h2>Introduction</h2> |
| |
| <p>detail/ct_gcd_lcm.hpp provides two compile-time algorithms: greatest |
| common divisor and least common multiple.</p> |
| |
| <h2>Synopsis</h2> |
| <pre class="code"> |
| namespace details { |
| namespace pool { |
| |
| template <unsigned A, unsigned B> |
| struct ct_gcd |
| { |
| static const unsigned value = ...; |
| }; |
| template <unsigned A, unsigned B> |
| struct ct_lcm |
| { |
| static const unsigned value = ...; |
| }; |
| |
| } // namespace pool |
| } // namespace details |
| </pre> |
| |
| <h2>Semantics</h2> |
| |
| <table align="center" border summary=""> |
| <caption> |
| <em>Symbol Table</em> |
| </caption> |
| |
| <tr> |
| <th>Symbol</th> |
| |
| <th>Meaning</th> |
| </tr> |
| |
| <tr> |
| <td class="code">A, B</td> |
| |
| <td>compile-time unsigned integer constants<a href= |
| "#s519p1"><sup>[5.19/1]</sup></a></td> |
| </tr> |
| </table><br> |
| |
| <table align="center" border summary=""> |
| <caption> |
| <em>Semantics</em> |
| </caption> |
| |
| <tr> |
| <th>Expression</th> |
| |
| <th>Result Type</th> |
| |
| <th>Value</th> |
| |
| <th>Precondition</th> |
| </tr> |
| |
| <tr> |
| <td class="code">ct_gcd<A, B>::value</td> |
| |
| <td>compile-time unsigned integer constant</td> |
| |
| <td>The greatest common divisor of <span class="code">A</span> and |
| <span class="code">B</span></td> |
| |
| <td class="code">A != 0 && B != 0</td> |
| </tr> |
| |
| <tr> |
| <td class="code">ct_lcm<A, B>::value</td> |
| |
| <td>compile-time unsigned integer constant</td> |
| |
| <td>The least common multiple of <span class="code">A</span> and |
| <span class="code">B</span></td> |
| |
| <td class="code">A != 0 && B != 0</td> |
| </tr> |
| </table> |
| |
| <h2>Notes</h2> |
| |
| <p>Since these are compile-time algorithms, violation of the preconditions |
| will result in a compile-time error.</p> |
| |
| <h2>Dependencies</h2> |
| |
| <ul> |
| <li><boost/static_assert.hpp> (see <a href= |
| "../../../static_assert/static_assert.htm">Boost.Static_Assert</a>), to |
| ensure preconditions are met.</li> |
| |
| <li><boost/type_traits/ice.hpp> (see <a href= |
| "http://www.boost.org/more/int_const_guidelines.htm">Coding Guidelines for |
| Integral Constant Expressions</a>), to help with portability.</li> |
| </ul> |
| |
| <h2>Selected Quotations from the Standard</h2> |
| |
| <p><a name="s519p1" id="s519p1"></a><strong>5.19/1: Expressions: Constant |
| Expressions:</strong> ". . . An <em>integral constant expression</em> can |
| involve only literals (2.13), enumerators, <span class="code">const</span> |
| variables or static data members of integral or enumeration types |
| initialized with constant expressions (8.5), non-type template parameters |
| of integral or enumeration types, and <span class="code">sizeof</span> |
| expressions. Floating literals (2.13.3) can appear only if they are cast to |
| integral or enumeration types. Only type conversions to integral or |
| enumeration types can be used. In particular, except in <span class= |
| "code">sizeof</span> expressions, functions, class objects, pointers, or |
| references shall not be used, and assignment, increment, decrement, |
| function-call, or comma operators shall not be used."</p> |
| |
| <h2>Future Directions</h2> |
| |
| <p>This header may be replaced by a Boost compile-time algorithms |
| library.</p> |
| <hr> |
| |
| <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src= |
| "../../../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional" |
| height="31" width="88"></a></p> |
| |
| <p>Revised |
| <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 |
| December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p> |
| |
| <p><i>Copyright © 2000, 2001 Stephen Cleary (scleary AT jerviswebb DOT |
| com)</i></p> |
| |
| <p><i>Distributed under the Boost Software License, Version 1.0. (See |
| accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> |
| or copy at <a href= |
| "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p> |
| </body> |
| </html> |
