2001-12-03 03:29:57 +00:00
|
|
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
|
2000-07-27 14:04:40 +00:00
|
|
|
<html>
|
|
|
|
|
<head>
|
|
|
|
|
<title>Integer Type Selection Templates</title>
|
|
|
|
|
</head>
|
|
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<body bgcolor="white" text="black">
|
2002-02-04 18:55:31 +00:00
|
|
|
<h1>
|
2004-10-05 15:45:52 +00:00
|
|
|
<img src="../../boost.png" alt="boost.png (6897 bytes)"
|
2001-12-03 03:29:57 +00:00
|
|
|
align="middle" width="277" height="86">Integer Type Selection
|
|
|
|
|
Templates</h1>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<p>The <cite><a
|
|
|
|
|
href="../../boost/integer.hpp"><boost/integer.hpp></a></cite> 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>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<h2><a name="contents">Contents</a></h2>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<ul>
|
|
|
|
|
<li><a href="#contents">Contents</a></li>
|
|
|
|
|
<li><a href="#synopsis">Synopsis</a></li>
|
|
|
|
|
<li><a href="#easy">Easiest-to-Manipulate Types</a></li>
|
|
|
|
|
<li><a href="#sized">Sized Types</a></li>
|
|
|
|
|
<li><a href="#example">Example</a></li>
|
|
|
|
|
<li><a href="#demo">Demonstration Program</a></li>
|
|
|
|
|
<li><a href="#rationale">Rationale</a></li>
|
|
|
|
|
<li><a href="#alternative">Alternative</a></li>
|
|
|
|
|
<li><a href="#credits">Credits</a></li>
|
|
|
|
|
</ul>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<h2><a name="synopsis">Synopsis</a></h2>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2002-02-04 18:55:31 +00:00
|
|
|
<blockquote><pre>namespace boost
|
2000-07-27 14:04:40 +00:00
|
|
|
{
|
|
|
|
|
// fast integers from least integers
|
2001-12-03 03:29:57 +00:00
|
|
|
template< typename LeastInt >
|
|
|
|
|
struct int_fast_t
|
|
|
|
|
{
|
|
|
|
|
typedef <em>implementation_supplied</em> fast;
|
|
|
|
|
};
|
2000-07-27 14:04:40 +00:00
|
|
|
|
|
|
|
|
// signed
|
2001-12-03 03:29:57 +00:00
|
|
|
template< int Bits >
|
2000-07-27 14:04:40 +00:00
|
|
|
struct int_t
|
|
|
|
|
{
|
2001-12-03 03:29:57 +00:00
|
|
|
typedef <em>implementation_supplied</em> least;
|
2000-07-27 14:04:40 +00:00
|
|
|
typedef int_fast_t<least>::fast fast;
|
|
|
|
|
};
|
|
|
|
|
|
|
|
|
|
// unsigned
|
2001-12-03 03:29:57 +00:00
|
|
|
template< int Bits >
|
2000-07-27 14:04:40 +00:00
|
|
|
struct uint_t
|
|
|
|
|
{
|
2001-12-03 03:29:57 +00:00
|
|
|
typedef <em>implementation_supplied</em> least;
|
2000-07-27 14:04:40 +00:00
|
|
|
typedef int_fast_t<least>::fast fast;
|
|
|
|
|
};
|
|
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
// signed
|
|
|
|
|
template< long MaxValue >
|
|
|
|
|
struct int_max_value_t
|
|
|
|
|
{
|
|
|
|
|
typedef <em>implementation_supplied</em> least;
|
|
|
|
|
typedef int_fast_t<least>::fast fast;
|
|
|
|
|
};
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
template< long MinValue >
|
|
|
|
|
struct int_min_value_t
|
|
|
|
|
{
|
|
|
|
|
typedef <em>implementation_supplied</em> least;
|
|
|
|
|
typedef int_fast_t<least>::fast fast;
|
|
|
|
|
};
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
// unsigned
|
|
|
|
|
template< unsigned long Value >
|
|
|
|
|
struct uint_value_t
|
|
|
|
|
{
|
|
|
|
|
typedef <em>implementation_supplied</em> least;
|
|
|
|
|
typedef int_fast_t<least>::fast fast;
|
|
|
|
|
};
|
|
|
|
|
} // namespace boost
|
|
|
|
|
</pre></blockquote>
|
|
|
|
|
|
|
|
|
|
<h2><a name="easy">Easiest-to-Manipulate Types</a></h2>
|
|
|
|
|
|
|
|
|
|
<p>The <code>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>char</code> objects may go faster
|
|
|
|
|
if they were converted to <code>int</code> objects before processing.
|
|
|
|
|
The input type, passed as the only template parameter, must be a
|
|
|
|
|
built-in integral type, except <code>bool</code>. Unsigned integral
|
|
|
|
|
types can be used, as well as signed integral types, despite the name.
|
|
|
|
|
The output type is given as the class member <code>fast</code>.</p>
|
|
|
|
|
|
|
|
|
|
<p><strong>Implementation Notes</strong><br>
|
|
|
|
|
By default, the output type is identical to the input type. Eventually,
|
|
|
|
|
this code's implementation should be conditionalized 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>
|
|
|
|
|
|
|
|
|
|
<h2><a name="sized">Sized Types</a></h2>
|
|
|
|
|
|
|
|
|
|
<p>The <code>int_t</code>, <code>uint_t</code>,
|
|
|
|
|
<code>int_max_value_t</code>, <code>int_min_value_t</code>, and
|
|
|
|
|
<code>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 class member <code>least</code>. The easiest-to-manipulate
|
|
|
|
|
version of that type is given by the class member <code>fast</code>.
|
|
|
|
|
The following table describes each template's criteria.</p>
|
|
|
|
|
|
|
|
|
|
<table border="1" cellpadding="5">
|
|
|
|
|
<caption>Criteria for the Sized Type Class Templates</caption>
|
|
|
|
|
<tr>
|
|
|
|
|
<th>Class Template</th>
|
|
|
|
|
<th>Template Parameter Mapping</th>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td><code>boost::int_t</code></td>
|
|
|
|
|
<td>The smallest built-in signed integral type with at least the
|
|
|
|
|
given number of 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 a
|
|
|
|
|
<code>long</code>.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td><code>boost::uint_t</code></td>
|
|
|
|
|
<td>The smallest built-in unsigned integral type with at least
|
|
|
|
|
the given number of bits. The parameter should be a positive
|
|
|
|
|
number. A compile-time error results if the parameter is
|
|
|
|
|
larger than the number of bits in an <code>unsigned
|
|
|
|
|
long</code>.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td><code>boost::int_max_value_t</code></td>
|
|
|
|
|
<td>The smallest built-in signed integral type that supports the
|
|
|
|
|
given value as a maximum. The parameter should be a
|
|
|
|
|
positive number.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td><code>boost::int_min_value_t</code></td>
|
|
|
|
|
<td>The smallest built-in signed integral type that supports the
|
|
|
|
|
given value as a minimum. The parameter should be a
|
|
|
|
|
negative number.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr>
|
|
|
|
|
<td><code>boost::uint_value_t</code></td>
|
|
|
|
|
<td>The smallest built-in unsigned integral type that supports
|
|
|
|
|
the given value as a maximum. The parameter should be a
|
|
|
|
|
positive number.</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</table>
|
|
|
|
|
|
|
|
|
|
<h2><a name="example">Example</a></h2>
|
|
|
|
|
|
2002-02-04 18:55:31 +00:00
|
|
|
<blockquote><pre>#include <boost/integer.hpp>
|
2001-12-03 03:29:57 +00:00
|
|
|
|
|
|
|
|
//...
|
|
|
|
|
|
|
|
|
|
int main()
|
|
|
|
|
{
|
|
|
|
|
boost::int_t<24>::least my_var;
|
|
|
|
|
//...
|
|
|
|
|
}
|
|
|
|
|
</pre></blockquote>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<h2><a name="demo">Demonstration Program</a></h2>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<p>The program <a href="integer_test.cpp">integer_test.cpp</a> is a
|
|
|
|
|
simplistic demonstration of the results from instantiating various
|
|
|
|
|
examples of the sized type class templates.</p>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<h2><a name="rationale">Rationale</a></h2>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
|
|
|
|
<p>The rationale for the design of the templates in this header includes:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
2001-12-03 03:29:57 +00:00
|
|
|
<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>
|
2000-07-27 14:04:40 +00:00
|
|
|
</ul>
|
|
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<h2><a name="alternative">Alternative</a></h2>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<p>If the number of bits required is known beforehand, it may be more
|
|
|
|
|
appropriate to use the types supplied in <cite><a
|
|
|
|
|
href="../../boost/cstdint.hpp"><boost/cstdint.hpp></a></cite>.</p>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<h2><a name="credits">Credits</a></h2>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<p>The author of most of the Boost integer type choosing templates is <a
|
|
|
|
|
href="../../people/beman_dawes.html">Beman Dawes</a>. He gives thanks
|
2002-02-04 18:55:31 +00:00
|
|
|
to Valentin Bonnard and
|
2001-12-03 03:29:57 +00:00
|
|
|
<a href="../../people/kevlin_henney.htm"> Kevlin Henney</a> for sharing
|
|
|
|
|
their designs for similar templates. <a
|
|
|
|
|
href="../../people/daryle_walker.html">Daryle Walker</a> designed the
|
|
|
|
|
value-based sized templates.</p>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<hr>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2001-12-03 03:29:57 +00:00
|
|
|
<p>Revised May 20, 2001</p>
|
2000-07-27 14:04:40 +00:00
|
|
|
|
2006-11-04 22:58:43 +00:00
|
|
|
<p>© Copyright Beman Dawes 1999. Use, modification, and distribution are
|
|
|
|
|
subject to the Boost Software License, Version 1.0. (See accompanying file <a
|
2008-02-09 13:02:45 +00:00
|
|
|
href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or a copy at <<a
|
2006-11-04 22:58:43 +00:00
|
|
|
href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>>.)</p>
|
2000-07-27 14:04:40 +00:00
|
|
|
</body>
|
2008-02-09 13:02:45 +00:00
|
|
|
</html>
|
