Blame - doc/html/boost_integer/integer.html - RealtimeRoboticsGroup/test

<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

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Types</a>

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The <code class="literal">int_fast_t</code> class template maps its input type to the

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next-largest type that the processor can manipulate the easiest, or to itself

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if the input type is already an easy-to-manipulate type. For instance, processing

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a bunch of <code class="literal">char</code> objects may go faster if they were converted

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to <code class="literal">int</code> objects before processing. The input type, passed

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as the only template parameter, must be a built-in integral type, except

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<code class="literal">bool</code>. Unsigned integral types can be used, as well as

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signed integral types. The output type is given as the nested type <code class="literal">fast</code>.

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Implementation Notes: By default, the output

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type is identical to the input type. Eventually, this code's implementation

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should be customized for each platform to give accurate mappings between

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the built-in types and the easiest-to-manipulate built-in types. Also, there

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is no guarantee that the output type actually is easier to manipulate than

the input type.

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<a name="boost_integer.integer.sized"></a><a class="link" href="integer.html#boost_integer.integer.sized" title="Sized Types">Sized Types</a>

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The <code class="literal">int_t</code>, <code class="literal">uint_t</code>, <code class="literal">int_max_value_t</code>,

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<code class="literal">int_min_value_t</code>, and <code class="literal">uint_value_t</code> class

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templates find the most appropiate built-in integral type for the given template

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parameter. This type is given by the nested type <code class="literal">least</code>.

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The easiest-to-manipulate version of that type is given by the nested type

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<code class="literal">fast</code>. The following table describes each template's criteria.

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<a name="boost_integer.integer.sized.criteria_for_the_sized_type_class_templates"></a>Table 1. Criteria for the Sized Type Class Templates

<col>

<col>

</colgroup>

<th>

Class Template

</th>

<th>

Template Parameter Mapping

</th>

</tr></thead>

<tbody>

<tr>

<td>

<code class="literal">boost::int_t<N>::least</code>

</td>

<td>

The smallest, built-in, signed integral type with at least N

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bits, including the sign bit. The parameter should be a positive

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number. A compile-time error results if the parameter is larger

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than the number of bits in the largest integer type.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::int_t<N>::fast</code>

</td>

<td>

The easiest-to-manipulate, built-in, signed integral type with

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at least N bits, including the sign bit. The

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parameter should be a positive number. A compile-time error results

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if the parameter is larger than the number of bits in the largest

integer type.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::int_t<N>::exact</code>

</td>

<td>

A built-in, signed integral type with exactly N

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bits, including the sign bit. The parameter should be a positive

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number. Note that the member exact is defined

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only if there exists a type with

exactly N bits.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::uint_t<N>::least</code>

</td>

<td>

The smallest, built-in, unsigned integral type with at least N

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bits. The parameter should be a positive number. A compile-time

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error results if the parameter is larger than the number of bits

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in the largest integer type.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::uint_t<N>::fast</code>

</td>

<td>

The easiest-to-manipulate, built-in, unsigned integral type with

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at least N bits. The parameter should be a

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positive number. A compile-time error results if the parameter

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is larger than the number of bits in the largest integer type.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::uint_t<N>::exact</code>

</td>

<td>

A built-in, unsigned integral type with exactly N

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bits. The parameter should be a positive number. A compile-time

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error results if the parameter is larger than the number of bits

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in the largest integer type. Note that the member exact

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is defined only if there exists

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a type with exactly N bits.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::int_max_value_t<V>::last</code>

</td>

<td>

The smallest, built-in, signed integral type that can hold all

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the values in the inclusive range 0 - V. The

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parameter should be a positive number.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::int_max_value_t<V>::fast</code>

</td>

<td>

The easiest-to-manipulate, built-in, signed integral type that

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can hold all the values in the inclusive range 0 - V.

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The parameter should be a positive number.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::int_min_value_t<V>::least</code>

</td>

<td>

The smallest, built-in, signed integral type that can hold all

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the values in the inclusive range V - 0. The

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parameter should be a negative number.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::int_min_value_t<V>::fast</code>

</td>

<td>

The easiest-to-manipulate, built-in, signed integral type that

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can hold all the values in the inclusive range V - 0.

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The parameter should be a negative number.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::uint_value_t<V>::least</code>

</td>

<td>

The smallest, built-in, unsigned integral type that can hold all

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positive values up to and including V. The

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parameter should be a positive number.

</td>

</tr>

<tr>

<td>

<code class="literal">boost::uint_value_t<V>::fast</code>

</td>

<td>

The easiest-to-manipulate, built-in, unsigned integral type that

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can hold all positive values up to and including V.

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The parameter should be a positive number.

</td>

</tr>

</tbody>

</table></div>

</div>

</div>

<a name="boost_integer.integer.example"></a><a class="link" href="integer.html#boost_integer.integer.example" title="Example">Example</a>

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<pre class="programlisting">#include <boost/integer.hpp>

//...

int main()

{

boost::int_t<24>::least my_var; // my_var has at least 24-bits

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//...

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// This one is guarenteed not to be truncated:

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boost::int_max_value_t<1000>::least my1000 = 1000;

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//...

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// This one is guarenteed not to be truncated, and as fast

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// to manipulate as possible, its size may be greater than

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// that of my1000:

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boost::int_max_value_t<1000>::fast my_fast1000 = 1000;

}

</pre>

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<a name="boost_integer.integer.demonstration_program"></a><a class="link" href="integer.html#boost_integer.integer.demonstration_program" title="Demonstration Program">Demonstration

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Program</a>

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The program <a href="../../../test/integer_test.cpp" target="_top">integer_test.cpp</a>

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is a simplistic demonstration of the results from instantiating various examples

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of the sized type class templates.

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<a name="boost_integer.integer.rationale"></a><a class="link" href="integer.html#boost_integer.integer.rationale" title="Rationale">Rationale</a>

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The rationale for the design of the templates in this header includes:

Avoid recursion because of concern about C++'s limited guaranteed recursion

depth (17).

</li>

Avoid macros on general principles.

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</li>

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Try to keep the design as simple as possible.

</li>

</ul></div>

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<a name="boost_integer.integer.alternative"></a><a class="link" href="integer.html#boost_integer.integer.alternative" title="Alternative">Alternative</a>

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If the number of bits required is known beforehand, it may be more appropriate

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to use the types supplied in <a href="../../../../../boost/cstdint.hpp" target="_top"><boost/cstdint.hpp></a>.

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<a name="boost_integer.integer.credits"></a><a class="link" href="integer.html#boost_integer.integer.credits" title="Credits">Credits</a>

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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

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gives thanks to Valentin Bonnard and <a href="http://www.boost.org/people/kevlin_henney.htm" target="_top">Kevlin

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Henney</a> for sharing their designs for similar templates. <a href="http://www.boost.org/people/daryle_walker.html" target="_top">Daryle

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Walker</a> designed the value-based sized templates.

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