433 lines
24 KiB
HTML
433 lines
24 KiB
HTML
<html>
|
||
<head>
|
||
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
|
||
<title>Integer Type Selection</title>
|
||
<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
|
||
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
|
||
<link rel="home" href="../index.html" title="Boost.Integer">
|
||
<link rel="up" href="../index.html" title="Boost.Integer">
|
||
<link rel="prev" href="traits.html" title="Integer Traits">
|
||
<link rel="next" href="gcd_lcm.html" title="Greatest Common Divisor and Least Common Multiple">
|
||
</head>
|
||
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
|
||
<table cellpadding="2" width="100%"><tr>
|
||
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
|
||
<td align="center"><a href="../../../../../index.html">Home</a></td>
|
||
<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
|
||
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
|
||
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
|
||
<td align="center"><a href="../../../../../more/index.htm">More</a></td>
|
||
</tr></table>
|
||
<hr>
|
||
<div class="spirit-nav">
|
||
<a accesskey="p" href="traits.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gcd_lcm.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
|
||
</div>
|
||
<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 class="toc">
|
||
<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 guaranteed 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 guaranteed 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" style="list-style-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="https://www.boost.org/people/beman_dawes.html" target="_top">Beman Dawes</a>.
|
||
He gives thanks to Valentin Bonnard and <a href="https://www.boost.org/people/kevlin_henney.htm" target="_top">Kevlin
|
||
Henney</a> for sharing their designs for similar templates. <a href="https://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="https://www.boost.org/LICENSE_1_0.txt" target="_top">https://www.boost.org/LICENSE_1_0.txt</a>)
|
||
</p>
|
||
</div></td>
|
||
</tr></table>
|
||
<hr>
|
||
<div class="spirit-nav">
|
||
<a accesskey="p" href="traits.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gcd_lcm.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
|
||
</div>
|
||
</body>
|
||
</html>
|