ceph/src/boost/libs/integer/doc/html/boost_integer/mask.html

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  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="boost_integer.mask"></a><a class="link" href="mask.html" title="Integer Masks">Integer Masks</a>
  28 </h2></div></div></div>
  29 <div class="toc"><dl class="toc">
  30 <dt><span class="section"><a href="mask.html#boost_integer.mask.overview">Overview</a></span></dt>
  31 <dt><span class="section"><a href="mask.html#boost_integer.mask.synopsis">Synopsis</a></span></dt>
  32 <dt><span class="section"><a href="mask.html#boost_integer.mask.single_bit_mask_class_template">Single
  33       Bit-Mask Class Template</a></span></dt>
  34 <dt><span class="section"><a href="mask.html#boost_integer.mask.group_bit_mask_class_template">Group
  35       Bit-Mask Class Template</a></span></dt>
  36 <dt><span class="section"><a href="mask.html#boost_integer.mask.implementation_notes">Implementation
  37       Notes</a></span></dt>
  38 <dt><span class="section"><a href="mask.html#boost_integer.mask.example">Example</a></span></dt>
  39 <dt><span class="section"><a href="mask.html#boost_integer.mask.demonstration_program">Demonstration
  40       Program</a></span></dt>
  41 <dt><span class="section"><a href="mask.html#boost_integer.mask.rationale">Rationale</a></span></dt>
  42 <dt><span class="section"><a href="mask.html#boost_integer.mask.credits">Credits</a></span></dt>
  43 </dl></div>
  44 <div class="section">
  45 <div class="titlepage"><div><div><h3 class="title">
  46 <a name="boost_integer.mask.overview"></a><a class="link" href="mask.html#boost_integer.mask.overview" title="Overview">Overview</a>
  47 </h3></div></div></div>
  48 <p>
  49         The class templates in <a href="../../../../../boost/integer/integer_mask.hpp" target="_top">&lt;boost/integer/integer_mask.hpp&gt;</a>
  50         provide bit masks for a certain bit position or a contiguous-bit pack of
  51         a certain size. The types of the masking constants come from the <a class="link" href="integer.html" title="Integer Type Selection">integer
  52         type selection templates</a> header.
  53       </p>
  54 </div>
  55 <div class="section">
  56 <div class="titlepage"><div><div><h3 class="title">
  57 <a name="boost_integer.mask.synopsis"></a><a class="link" href="mask.html#boost_integer.mask.synopsis" title="Synopsis">Synopsis</a>
  58 </h3></div></div></div>
  59 <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>
  60
  61 <span class="keyword">namespace</span> <span class="identifier">boost</span>
  62 <span class="special">{</span>
  63
  64 <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>
  65 <span class="keyword">struct</span> <span class="identifier">high_bit_mask_t</span>
  66 <span class="special">{</span>
  67     <span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span>  <span class="identifier">least</span><span class="special">;</span>
  68     <span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span>  <span class="identifier">fast</span><span class="special">;</span>
  69
  70     <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>
  71     <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>
  72
  73     <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>
  74 <span class="special">};</span>
  75
  76 <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>
  77 <span class="keyword">struct</span> <span class="identifier">low_bits_mask_t</span>
  78 <span class="special">{</span>
  79     <span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span>  <span class="identifier">least</span><span class="special">;</span>
  80     <span class="keyword">typedef</span> <span class="emphasis"><em>implementation-defined-type</em></span>  <span class="identifier">fast</span><span class="special">;</span>
  81
  82     <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>
  83     <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>
  84
  85     <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>
  86 <span class="special">};</span>
  87
  88 <span class="comment">// Specializations for low_bits_mask_t exist for certain bit counts.</span>
  89
  90 <span class="special">}</span>  <span class="comment">// namespace boost</span>
  91 </pre>
  92 </div>
  93 <div class="section">
  94 <div class="titlepage"><div><div><h3 class="title">
  95 <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
  96       Bit-Mask Class Template</a>
  97 </h3></div></div></div>
  98 <p>
  99         The <code class="literal">boost::high_bit_mask_t</code> class template provides constants
 100         for bit masks representing the bit at a certain position. The masks are equivalent
 101         to the value 2<sup>Bit</sup>, where <code class="literal">Bit</code> is the template parameter.
 102         The bit position must be a nonnegative number from zero to <span class="emphasis"><em>Max</em></span>,
 103         where Max is one less than the number of bits supported by the largest unsigned
 104         built-in integral type. The following table describes the members of an instantiation
 105         of <code class="literal">high_bit_mask_t</code>.
 106       </p>
 107 <div class="table">
 108 <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>
 109         Class Template</b></p>
 110 <div class="table-contents"><table class="table" summary="Members of the boost::high_bit_mask_t
 111         Class Template">
 112 <colgroup>
 113 <col>
 114 <col>
 115 </colgroup>
 116 <thead><tr>
 117 <th>
 118                 <p>
 119                   Member
 120                 </p>
 121               </th>
 122 <th>
 123                 <p>
 124                   Meaning
 125                 </p>
 126               </th>
 127 </tr></thead>
 128 <tbody>
 129 <tr>
 130 <td>
 131                 <p>
 132                   <code class="literal">least</code>
 133                 </p>
 134               </td>
 135 <td>
 136                 <p>
 137                   The smallest, unsigned, built-in type that supports the given bit
 138                   position.
 139                 </p>
 140               </td>
 141 </tr>
 142 <tr>
 143 <td>
 144                 <p>
 145                   <code class="literal">fast</code>
 146                 </p>
 147               </td>
 148 <td>
 149                 <p>
 150                   The easiest-to-manipulate analog of <code class="literal">least</code>.
 151                 </p>
 152               </td>
 153 </tr>
 154 <tr>
 155 <td>
 156                 <p>
 157                   <code class="literal">high_bit</code>
 158                 </p>
 159               </td>
 160 <td>
 161                 <p>
 162                   A <code class="literal">least</code> constant of the value 2<sup>Bit</sup>.
 163                 </p>
 164               </td>
 165 </tr>
 166 <tr>
 167 <td>
 168                 <p>
 169                   <code class="literal">high_bit_fast</code>
 170                 </p>
 171               </td>
 172 <td>
 173                 <p>
 174                   A <code class="literal">fast</code> analog of <code class="literal">high_bit</code>.
 175                 </p>
 176               </td>
 177 </tr>
 178 <tr>
 179 <td>
 180                 <p>
 181                   <code class="literal">bit_position</code>
 182                 </p>
 183               </td>
 184 <td>
 185                 <p>
 186                   The value of the template parameter, in case its needed from a
 187                   renamed instantiation of the class template.
 188                 </p>
 189               </td>
 190 </tr>
 191 </tbody>
 192 </table></div>
 193 </div>
 194 <br class="table-break">
 195 </div>
 196 <div class="section">
 197 <div class="titlepage"><div><div><h3 class="title">
 198 <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
 199       Bit-Mask Class Template</a>
 200 </h3></div></div></div>
 201 <p>
 202         The <code class="literal">boost::low_bits_mask_t</code> class template provides constants
 203         for bit masks equivalent to the value (2<sup>Bits</sup> - 1), where <code class="literal">Bits</code>
 204         is the template parameter. The parameter <code class="literal">Bits</code> must be
 205         a non-negative integer from zero to <span class="emphasis"><em>Max</em></span>, where Max is
 206         the number of bits supported by the largest, unsigned, built-in integral
 207         type. The following table describes the members of <code class="literal">low_bits_mask_t</code>.
 208       </p>
 209 <div class="table">
 210 <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>
 211 <div class="table-contents"><table class="table" summary="Members of the boost::low_bits_mask_t Class Template">
 212 <colgroup>
 213 <col>
 214 <col>
 215 </colgroup>
 216 <thead><tr>
 217 <th>
 218                 <p>
 219                   Member
 220                 </p>
 221               </th>
 222 <th>
 223                 <p>
 224                   Meaning
 225                 </p>
 226               </th>
 227 </tr></thead>
 228 <tbody>
 229 <tr>
 230 <td>
 231                 <p>
 232                   <code class="literal">least</code>
 233                 </p>
 234               </td>
 235 <td>
 236                 <p>
 237                   The smallest, unsigned built-in type that supports the given bit
 238                   count.
 239                 </p>
 240               </td>
 241 </tr>
 242 <tr>
 243 <td>
 244                 <p>
 245                   <code class="literal">fast</code>
 246                 </p>
 247               </td>
 248 <td>
 249                 <p>
 250                   The easiest-to-manipulate analog of <code class="literal">least</code>.
 251                 </p>
 252               </td>
 253 </tr>
 254 <tr>
 255 <td>
 256                 <p>
 257                   <code class="literal">sig_bits</code>
 258                 </p>
 259               </td>
 260 <td>
 261                 <p>
 262                   A <code class="literal">least</code> constant of the desired bit-masking
 263                   value.
 264                 </p>
 265               </td>
 266 </tr>
 267 <tr>
 268 <td>
 269                 <p>
 270                   <code class="literal">sig_bits_fast</code>
 271                 </p>
 272               </td>
 273 <td>
 274                 <p>
 275                   A <code class="literal">fast</code> analog of <code class="literal">sig_bits</code>.
 276                 </p>
 277               </td>
 278 </tr>
 279 <tr>
 280 <td>
 281                 <p>
 282                   <code class="literal">bit_count</code>
 283                 </p>
 284               </td>
 285 <td>
 286                 <p>
 287                   The value of the template parameter, in case its needed from a
 288                   renamed instantiation of the class template.
 289                 </p>
 290               </td>
 291 </tr>
 292 </tbody>
 293 </table></div>
 294 </div>
 295 <br class="table-break">
 296 </div>
 297 <div class="section">
 298 <div class="titlepage"><div><div><h3 class="title">
 299 <a name="boost_integer.mask.implementation_notes"></a><a class="link" href="mask.html#boost_integer.mask.implementation_notes" title="Implementation Notes">Implementation
 300       Notes</a>
 301 </h3></div></div></div>
 302 <p>
 303         When <code class="literal">Bits</code> is the exact size of a built-in unsigned type,
 304         the implementation has to change to prevent undefined behavior. Therefore,
 305         there are specializations of <code class="literal">low_bits_mask_t</code> at those
 306         bit counts.
 307       </p>
 308 </div>
 309 <div class="section">
 310 <div class="titlepage"><div><div><h3 class="title">
 311 <a name="boost_integer.mask.example"></a><a class="link" href="mask.html#boost_integer.mask.example" title="Example">Example</a>
 312 </h3></div></div></div>
 313 <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>
 314
 315 <span class="comment">//...</span>
 316
 317 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
 318 <span class="special">{</span>
 319     <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>
 320     <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>
 321
 322     <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>
 323     <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>
 324     <span class="comment">//...</span>
 325
 326     <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>
 327     <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>
 328
 329     <span class="comment">//...</span>
 330 <span class="special">}</span>
 331 </pre>
 332 </div>
 333 <div class="section">
 334 <div class="titlepage"><div><div><h3 class="title">
 335 <a name="boost_integer.mask.demonstration_program"></a><a class="link" href="mask.html#boost_integer.mask.demonstration_program" title="Demonstration Program">Demonstration
 336       Program</a>
 337 </h3></div></div></div>
 338 <p>
 339         The program <a href="../../../test/integer_mask_test.cpp" target="_top">integer_mask_test.cpp</a>
 340         is a simplistic demonstration of the results from instantiating various examples
 341         of the bit mask class templates.
 342       </p>
 343 </div>
 344 <div class="section">
 345 <div class="titlepage"><div><div><h3 class="title">
 346 <a name="boost_integer.mask.rationale"></a><a class="link" href="mask.html#boost_integer.mask.rationale" title="Rationale">Rationale</a>
 347 </h3></div></div></div>
 348 <p>
 349         The class templates in this header are an extension of the <a class="link" href="integer.html" title="Integer Type Selection">integer
 350         type selection class templates</a>. The new class templates provide the
 351         same sized types, but also convenient masks to use when extracting the highest
 352         or all the significant bits when the containing built-in type contains more
 353         bits. This prevents contamination of values by the higher, unused bits.
 354       </p>
 355 </div>
 356 <div class="section">
 357 <div class="titlepage"><div><div><h3 class="title">
 358 <a name="boost_integer.mask.credits"></a><a class="link" href="mask.html#boost_integer.mask.credits" title="Credits">Credits</a>
 359 </h3></div></div></div>
 360 <p>
 361         The author of the Boost bit mask class templates is <a href="http://www.boost.org/people/daryle_walker.html" target="_top">Daryle
 362         Walker</a>.
 363       </p>
 364 </div>
 365 </div>
 366 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 367 <td align="left"></td>
 368 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2009 Beman
 369       Dawes, Daryle Walker, Gennaro Prota, John Maddock<p>
 370         Distributed under the Boost Software License, Version 1.0. (See accompanying
 371         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>)
 372       </p>
 373 </div></td>
 374 </tr></table>
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