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| <div class="section"> |
| <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"> |
| <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"> |
| <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"> |
| <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="boost_integer.integer.sized.criteria_for_the_sized_type_class_templates"></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"> |
| <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"> |
| <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"> |
| <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 class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| Avoid recursion because of concern about C++'s limited guaranteed recursion |
| depth (17). |
| </li> |
| <li class="listitem"> |
| Avoid macros on general principles. |
| </li> |
| <li class="listitem"> |
| Try to keep the design as simple as possible. |
| </li> |
| </ul></div> |
| </div> |
| <div class="section"> |
| <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"> |
| <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>) |
| </p> |
| </div></td> |
| </tr></table> |
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