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<title>Integer Type Selection</title>
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<div class="section" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_integer.integer"></a><a class="link" href="integer.html" title="Integer Type Selection"> Integer Type Selection</a>
</h2></div></div></div>
<div class="toc"><dl>
<dt><span class="section"><a href="integer.html#boost_integer.integer.synopsis"> Synopsis</a></span></dt>
<dt><span class="section"><a href="integer.html#boost_integer.integer.easiest"> Easiest-to-Manipulate
Types</a></span></dt>
<dt><span class="section"><a href="integer.html#boost_integer.integer.sized"> Sized Types</a></span></dt>
<dt><span class="section"><a href="integer.html#boost_integer.integer.example">Example</a></span></dt>
<dt><span class="section"><a href="integer.html#boost_integer.integer.demonstration_program">Demonstration
Program</a></span></dt>
<dt><span class="section"><a href="integer.html#boost_integer.integer.rationale">Rationale</a></span></dt>
<dt><span class="section"><a href="integer.html#boost_integer.integer.alternative">Alternative</a></span></dt>
<dt><span class="section"><a href="integer.html#boost_integer.integer.credits">Credits</a></span></dt>
</dl></div>
<p>
The <a href="../../../../../boost/integer.hpp" target="_top"><boost/integer.hpp></a>
type selection templates allow integer types to be selected based on desired
characteristics such as number of bits or maximum value. This facility is particularly
useful for solving generic programming problems.
</p>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.synopsis"></a><a class="link" href="integer.html#boost_integer.integer.synopsis" title="Synopsis"> Synopsis</a>
</h3></div></div></div>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
<span class="special">{</span>
<span class="comment">// fast integers from least integers
</span> <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">LeastInt</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">int_fast_t</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>
<span class="comment">// signed
</span> <span class="keyword">template</span><span class="special"><</span><span class="keyword">int</span> <span class="identifier">Bits</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">int_t</span>
<span class="special">{</span>
<span class="comment">/* Member exact may or may not be defined depending upon Bits */</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">exact</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">least</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">int_fast_t</span><span class="special"><</span><span class="identifier">least</span><span class="special">>::</span><span class="identifier">fast</span> <span class="identifier">fast</span><span class="special">;</span>
<span class="special">};</span>
<span class="comment">// unsigned
</span> <span class="keyword">template</span><span class="special"><</span><span class="keyword">int</span> <span class="identifier">Bits</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">uint_t</span>
<span class="special">{</span>
<span class="comment">/* Member exact may or may not be defined depending upon Bits */</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">exact</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">least</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">int_fast_t</span><span class="special"><</span><span class="identifier">least</span><span class="special">>::</span><span class="identifier">fast</span> <span class="identifier">fast</span><span class="special">;</span>
<span class="special">};</span>
<span class="comment">// signed
</span> <span class="keyword">template</span><span class="special"><</span><span class="keyword">long</span> <span class="keyword">long</span> <span class="identifier">MaxValue</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">int_max_value_t</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">least</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">int_fast_t</span><span class="special"><</span><span class="identifier">least</span><span class="special">>::</span><span class="identifier">fast</span> <span class="identifier">fast</span><span class="special">;</span>
<span class="special">};</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">long</span> <span class="keyword">long</span> <span class="identifier">MinValue</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">int_min_value_t</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">least</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">int_fast_t</span><span class="special"><</span><span class="identifier">least</span><span class="special">>::</span><span class="identifier">fast</span> <span class="identifier">fast</span><span class="special">;</span>
<span class="special">};</span>
<span class="comment">// unsigned
</span> <span class="keyword">template</span><span class="special"><</span><span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span> <span class="identifier">Value</span><span class="special">></span>
<span class="keyword">struct</span> <span class="identifier">uint_value_t</span>
<span class="special">{</span>
<span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span> <span class="identifier">least</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">int_fast_t</span><span class="special"><</span><span class="identifier">least</span><span class="special">>::</span><span class="identifier">fast</span> <span class="identifier">fast</span><span class="special">;</span>
<span class="special">};</span>
<span class="special">}</span> <span class="comment">// namespace boost
</span></pre>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.easiest"></a><a class="link" href="integer.html#boost_integer.integer.easiest" title="Easiest-to-Manipulate Types"> Easiest-to-Manipulate
Types</a>
</h3></div></div></div>
<p>
The <code class="literal">int_fast_t</code> class template maps its input type to the
next-largest type that the processor can manipulate the easiest, or to itself
if the input type is already an easy-to-manipulate type. For instance, processing
a bunch of <code class="literal">char</code> objects may go faster if they were converted
to <code class="literal">int</code> objects before processing. The input type, passed
as the only template parameter, must be a built-in integral type, except
<code class="literal">bool</code>. Unsigned integral types can be used, as well as
signed integral types. The output type is given as the nested type <code class="literal">fast</code>.
</p>
<p>
<span class="bold"><strong>Implementation Notes:</strong></span> By default, the output
type is identical to the input type. Eventually, this code's implementation
should be customized for each platform to give accurate mappings between
the built-in types and the easiest-to-manipulate built-in types. Also, there
is no guarantee that the output type actually is easier to manipulate than
the input type.
</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.sized"></a><a class="link" href="integer.html#boost_integer.integer.sized" title="Sized Types"> Sized Types</a>
</h3></div></div></div>
<p>
The <code class="literal">int_t</code>, <code class="literal">uint_t</code>, <code class="literal">int_max_value_t</code>,
<code class="literal">int_min_value_t</code>, and <code class="literal">uint_value_t</code> class
templates find the most appropiate built-in integral type for the given template
parameter. This type is given by the nested type <code class="literal">least</code>.
The easiest-to-manipulate version of that type is given by the nested type
<code class="literal">fast</code>. The following table describes each template's criteria.
</p>
<div class="table">
<a name="id781665"></a><p class="title"><b>Table 1. Criteria for the Sized Type Class Templates</b></p>
<div class="table-contents"><table class="table" summary="Criteria for the Sized Type Class Templates">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Class Template
</p>
</th>
<th>
<p>
Template Parameter Mapping
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="literal">boost::int_t<N>::least</code>
</p>
</td>
<td>
<p>
The smallest, built-in, signed integral type with at least <span class="emphasis"><em>N</em></span>
bits, including the sign bit. The parameter should be a positive number.
A compile-time error results if the parameter is larger than the number
of bits in the largest integer type.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::int_t<N>::fast</code>
</p>
</td>
<td>
<p>
The easiest-to-manipulate, built-in, signed integral type with at least
<span class="emphasis"><em>N</em></span> bits, including the sign bit. The parameter
should be a positive number. A compile-time error results if the parameter
is larger than the number of bits in the largest integer type.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::int_t<N>::exact</code>
</p>
</td>
<td>
<p>
A built-in, signed integral type with exactly <span class="emphasis"><em>N</em></span>
bits, including the sign bit. The parameter should be a positive number.
Note that the member <span class="emphasis"><em>exact</em></span> is defined <span class="bold"><strong>only</strong></span> if there exists a type with exactly <span class="emphasis"><em>N</em></span>
bits.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::uint_t<N>::least</code>
</p>
</td>
<td>
<p>
The smallest, built-in, unsigned integral type with at least <span class="emphasis"><em>N</em></span>
bits. The parameter should be a positive number. A compile-time error
results if the parameter is larger than the number of bits in the largest
integer type.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::uint_t<N>::fast</code>
</p>
</td>
<td>
<p>
The easiest-to-manipulate, built-in, unsigned integral type with at
least <span class="emphasis"><em>N</em></span> bits. The parameter should be a positive
number. A compile-time error results if the parameter is larger than
the number of bits in the largest integer type.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::uint_t<N>::exact</code>
</p>
</td>
<td>
<p>
A built-in, unsigned integral type with exactly <span class="emphasis"><em>N</em></span>
bits. The parameter should be a positive number. A compile-time error
results if the parameter is larger than the number of bits in the largest
integer type. Note that the member <span class="emphasis"><em>exact</em></span> is defined
<span class="bold"><strong>only</strong></span> if there exists a type with exactly
N bits.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::int_max_value_t<V>::last</code>
</p>
</td>
<td>
<p>
The smallest, built-in, signed integral type that can hold all the
values in the inclusive range <span class="emphasis"><em>0 - V</em></span>. The parameter
should be a positive number.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::int_max_value_t<V>::fast</code>
</p>
</td>
<td>
<p>
The easiest-to-manipulate, built-in, signed integral type that can
hold all the values in the inclusive range <span class="emphasis"><em>0 - V</em></span>.
The parameter should be a positive number.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::int_min_value_t<V>::least</code>
</p>
</td>
<td>
<p>
The smallest, built-in, signed integral type that can hold all the
values in the inclusive range <span class="emphasis"><em>V - 0</em></span>. The parameter
should be a negative number.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::int_min_value_t<V>::fast</code>
</p>
</td>
<td>
<p>
The easiest-to-manipulate, built-in, signed integral type that can
hold all the values in the inclusive range <span class="emphasis"><em>V - 0</em></span>.
The parameter should be a negative number.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::uint_value_t<V>::least</code>
</p>
</td>
<td>
<p>
The smallest, built-in, unsigned integral type that can hold all positive
values up to and including <span class="emphasis"><em>V</em></span>. The parameter should
be a positive number.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">boost::uint_value_t<V>::fast</code>
</p>
</td>
<td>
<p>
The easiest-to-manipulate, built-in, unsigned integral type that can
hold all positive values up to and including <span class="emphasis"><em>V</em></span>.
The parameter should be a positive number.
</p>
</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break">
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.example"></a><a class="link" href="integer.html#boost_integer.integer.example" title="Example">Example</a>
</h3></div></div></div>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">integer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="comment">//...
</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">int_t</span><span class="special"><</span><span class="number">24</span><span class="special">>::</span><span class="identifier">least</span> <span class="identifier">my_var</span><span class="special">;</span> <span class="comment">// my_var has at least 24-bits
</span> <span class="comment">//...
</span> <span class="comment">// This one is guarenteed not to be truncated:
</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">int_max_value_t</span><span class="special"><</span><span class="number">1000</span><span class="special">>::</span><span class="identifier">least</span> <span class="identifier">my1000</span> <span class="special">=</span> <span class="number">1000</span><span class="special">;</span>
<span class="comment">//...
</span> <span class="comment">// This one is guarenteed not to be truncated, and as fast
</span> <span class="comment">// to manipulate as possible, its size may be greater than
</span> <span class="comment">// that of my1000:
</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">int_max_value_t</span><span class="special"><</span><span class="number">1000</span><span class="special">>::</span><span class="identifier">fast</span> <span class="identifier">my_fast1000</span> <span class="special">=</span> <span class="number">1000</span><span class="special">;</span>
<span class="special">}</span>
</pre>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.demonstration_program"></a><a class="link" href="integer.html#boost_integer.integer.demonstration_program" title="Demonstration Program">Demonstration
Program</a>
</h3></div></div></div>
<p>
The program <a href="../../../test/integer_test.cpp" target="_top">integer_test.cpp</a>
is a simplistic demonstration of the results from instantiating various examples
of the sized type class templates.
</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.rationale"></a><a class="link" href="integer.html#boost_integer.integer.rationale" title="Rationale">Rationale</a>
</h3></div></div></div>
<p>
The rationale for the design of the templates in this header includes:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
Avoid recursion because of concern about C++'s limited guaranteed recursion
depth (17).
</li>
<li>
Avoid macros on general principles.
</li>
<li>
Try to keep the design as simple as possible.
</li>
</ul></div>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.alternative"></a><a class="link" href="integer.html#boost_integer.integer.alternative" title="Alternative">Alternative</a>
</h3></div></div></div>
<p>
If the number of bits required is known beforehand, it may be more appropriate
to use the types supplied in <a href="../../../../../boost/cstdint.hpp" target="_top"><boost/cstdint.hpp></a>.
</p>
</div>
<div class="section" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.integer.credits"></a><a class="link" href="integer.html#boost_integer.integer.credits" title="Credits">Credits</a>
</h3></div></div></div>
<p>
The author of most of the Boost integer type choosing templates is <a href="http://www.boost.org/people/beman_dawes.html" target="_top">Beman Dawes</a>. He
gives thanks to Valentin Bonnard and <a href="http://www.boost.org/people/kevlin_henney.htm" target="_top">Kevlin
Henney</a> for sharing their designs for similar templates. <a href="http://www.boost.org/people/daryle_walker.html" target="_top">Daryle
Walker</a> designed the value-based sized templates.
</p>
</div>
</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 © 2001 -2009 Beman Dawes, Daryle Walker, Gennaro Prota,
John Maddock<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>)
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