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<title>ct_gcd_lcm - Compile-Time GCD and LCM</title>
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<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>
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<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>
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