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<title>Integer Masks</title>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_integer.mask"></a><a class="link" href="mask.html" title="Integer Masks">Integer Masks</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="mask.html#boost_integer.mask.overview">Overview</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.synopsis">Synopsis</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.single_bit_mask_class_template">Single
      Bit-Mask Class Template</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.group_bit_mask_class_template">Group
      Bit-Mask Class Template</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.implementation_notes">Implementation
      Notes</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.example">Example</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.demonstration_program">Demonstration
      Program</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.rationale">Rationale</a></span></dt>
<dt><span class="section"><a href="mask.html#boost_integer.mask.credits">Credits</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.mask.overview"></a><a class="link" href="mask.html#boost_integer.mask.overview" title="Overview">Overview</a>
</h3></div></div></div>
<p>
        The class templates in <a href="../../../../../boost/integer/integer_mask.hpp" target="_top">&lt;boost/integer/integer_mask.hpp&gt;</a>
        provide bit masks for a certain bit position or a contiguous-bit pack of
        a certain size. The types of the masking constants come from the <a class="link" href="integer.html" title="Integer Type Selection">integer
        type selection templates</a> header.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.mask.synopsis"></a><a class="link" href="mask.html#boost_integer.mask.synopsis" title="Synopsis">Synopsis</a>
</h3></div></div></div>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cstddef</span><span class="special">&gt;</span>  <span class="comment">// for std::size_t</span>

<span class="keyword">namespace</span> <span class="identifier">boost</span>
<span class="special">{</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">Bit</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">high_bit_mask_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="emphasis"><em>implementation-defined-type</em></span>  <span class="identifier">fast</span><span class="special">;</span>

    <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">least</span>       <span class="identifier">high_bit</span>       <span class="special">=</span> <span class="emphasis"><em>implementation-defined</em></span><span class="special">;</span>
    <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">fast</span>        <span class="identifier">high_bit_fast</span>  <span class="special">=</span> <span class="emphasis"><em>implementation-defined</em></span><span class="special">;</span>

    <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bit_position</span>   <span class="special">=</span> <span class="identifier">Bit</span><span class="special">;</span>
<span class="special">};</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">Bits</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">low_bits_mask_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="emphasis"><em>implementation-defined-type</em></span>  <span class="identifier">fast</span><span class="special">;</span>

    <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">least</span>       <span class="identifier">sig_bits</span>       <span class="special">=</span> <span class="emphasis"><em>implementation-defined</em></span><span class="special">;</span>
    <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">fast</span>        <span class="identifier">sig_bits_fast</span>  <span class="special">=</span> <span class="emphasis"><em>implementation-defined</em></span><span class="special">;</span>

    <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bit_count</span>      <span class="special">=</span> <span class="identifier">Bits</span><span class="special">;</span>
<span class="special">};</span>

<span class="comment">// Specializations for low_bits_mask_t exist for certain bit counts.</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.mask.single_bit_mask_class_template"></a><a class="link" href="mask.html#boost_integer.mask.single_bit_mask_class_template" title="Single Bit-Mask Class Template">Single
      Bit-Mask Class Template</a>
</h3></div></div></div>
<p>
        The <code class="literal">boost::high_bit_mask_t</code> class template provides constants
        for bit masks representing the bit at a certain position. The masks are equivalent
        to the value 2<sup>Bit</sup>, where <code class="literal">Bit</code> is the template parameter.
        The bit position must be a nonnegative number from zero to <span class="emphasis"><em>Max</em></span>,
        where Max is one less than the number of bits supported by the largest unsigned
        built-in integral type. The following table describes the members of an instantiation
        of <code class="literal">high_bit_mask_t</code>.
      </p>
<div class="table">
<a name="boost_integer.mask.single_bit_mask_class_template.members_of_the__boost__high_bit_mask_t__class_template"></a><p class="title"><b>Table&#160;2.&#160;Members of the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">high_bit_mask_t</span></code>
        Class Template</b></p>
<div class="table-contents"><table class="table" summary="Members of the boost::high_bit_mask_t
        Class Template">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Member
                </p>
              </th>
<th>
                <p>
                  Meaning
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <code class="literal">least</code>
                </p>
              </td>
<td>
                <p>
                  The smallest, unsigned, built-in type that supports the given bit
                  position.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">fast</code>
                </p>
              </td>
<td>
                <p>
                  The easiest-to-manipulate analog of <code class="literal">least</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">high_bit</code>
                </p>
              </td>
<td>
                <p>
                  A <code class="literal">least</code> constant of the value 2<sup>Bit</sup>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">high_bit_fast</code>
                </p>
              </td>
<td>
                <p>
                  A <code class="literal">fast</code> analog of <code class="literal">high_bit</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">bit_position</code>
                </p>
              </td>
<td>
                <p>
                  The value of the template parameter, in case its needed from a
                  renamed instantiation of the class template.
                </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.mask.group_bit_mask_class_template"></a><a class="link" href="mask.html#boost_integer.mask.group_bit_mask_class_template" title="Group Bit-Mask Class Template">Group
      Bit-Mask Class Template</a>
</h3></div></div></div>
<p>
        The <code class="literal">boost::low_bits_mask_t</code> class template provides constants
        for bit masks equivalent to the value (2<sup>Bits</sup> - 1), where <code class="literal">Bits</code>
        is the template parameter. The parameter <code class="literal">Bits</code> must be
        a non-negative integer from zero to <span class="emphasis"><em>Max</em></span>, where Max is
        the number of bits supported by the largest, unsigned, built-in integral
        type. The following table describes the members of <code class="literal">low_bits_mask_t</code>.
      </p>
<div class="table">
<a name="boost_integer.mask.group_bit_mask_class_template.members_of_the___boost__low_bits_mask_t__class_template"></a><p class="title"><b>Table&#160;3.&#160;Members of the <code class="literal">boost::low_bits_mask_t</code> Class Template</b></p>
<div class="table-contents"><table class="table" summary="Members of the boost::low_bits_mask_t Class Template">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  Member
                </p>
              </th>
<th>
                <p>
                  Meaning
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <code class="literal">least</code>
                </p>
              </td>
<td>
                <p>
                  The smallest, unsigned built-in type that supports the given bit
                  count.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">fast</code>
                </p>
              </td>
<td>
                <p>
                  The easiest-to-manipulate analog of <code class="literal">least</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">sig_bits</code>
                </p>
              </td>
<td>
                <p>
                  A <code class="literal">least</code> constant of the desired bit-masking
                  value.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">sig_bits_fast</code>
                </p>
              </td>
<td>
                <p>
                  A <code class="literal">fast</code> analog of <code class="literal">sig_bits</code>.
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="literal">bit_count</code>
                </p>
              </td>
<td>
                <p>
                  The value of the template parameter, in case its needed from a
                  renamed instantiation of the class template.
                </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.mask.implementation_notes"></a><a class="link" href="mask.html#boost_integer.mask.implementation_notes" title="Implementation Notes">Implementation
      Notes</a>
</h3></div></div></div>
<p>
        When <code class="literal">Bits</code> is the exact size of a built-in unsigned type,
        the implementation has to change to prevent undefined behavior. Therefore,
        there are specializations of <code class="literal">low_bits_mask_t</code> at those
        bit counts.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.mask.example"></a><a class="link" href="mask.html#boost_integer.mask.example" title="Example">Example</a>
</h3></div></div></div>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">integer</span><span class="special">/</span><span class="identifier">integer_mask</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</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="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">high_bit_mask_t</span><span class="special">&lt;</span><span class="number">29</span><span class="special">&gt;</span>  <span class="identifier">mask1_type</span><span class="special">;</span>
    <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">low_bits_mask_t</span><span class="special">&lt;</span><span class="number">15</span><span class="special">&gt;</span>  <span class="identifier">mask2_type</span><span class="special">;</span>

    <span class="identifier">mask1_type</span><span class="special">::</span><span class="identifier">least</span>  <span class="identifier">my_var1</span><span class="special">;</span>
    <span class="identifier">mask2_type</span><span class="special">::</span><span class="identifier">fast</span>   <span class="identifier">my_var2</span><span class="special">;</span>
    <span class="comment">//...</span>

    <span class="identifier">my_var1</span> <span class="special">|=</span> <span class="identifier">mask1_type</span><span class="special">::</span><span class="identifier">high_bit</span><span class="special">;</span>
    <span class="identifier">my_var2</span> <span class="special">&amp;=</span> <span class="identifier">mask2_type</span><span class="special">::</span><span class="identifier">sig_bits_fast</span><span class="special">;</span>

    <span class="comment">//...</span>
<span class="special">}</span>
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.mask.demonstration_program"></a><a class="link" href="mask.html#boost_integer.mask.demonstration_program" title="Demonstration Program">Demonstration
      Program</a>
</h3></div></div></div>
<p>
        The program <a href="../../../test/integer_mask_test.cpp" target="_top">integer_mask_test.cpp</a>
        is a simplistic demonstration of the results from instantiating various examples
        of the bit mask class templates.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.mask.rationale"></a><a class="link" href="mask.html#boost_integer.mask.rationale" title="Rationale">Rationale</a>
</h3></div></div></div>
<p>
        The class templates in this header are an extension of the <a class="link" href="integer.html" title="Integer Type Selection">integer
        type selection class templates</a>. The new class templates provide the
        same sized types, but also convenient masks to use when extracting the highest
        or all the significant bits when the containing built-in type contains more
        bits. This prevents contamination of values by the higher, unused bits.
      </p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_integer.mask.credits"></a><a class="link" href="mask.html#boost_integer.mask.credits" title="Credits">Credits</a>
</h3></div></div></div>
<p>
        The author of the Boost bit mask class templates is <a href="http://www.boost.org/people/daryle_walker.html" target="_top">Daryle
        Walker</a>.
      </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 &#169; 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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