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