1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Integer Masks</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Boost.Integer"> 8<link rel="up" href="../index.html" title="Boost.Integer"> 9<link rel="prev" href="mod_inverse.html" title="Modular Multiplicative Inverse"> 10<link rel="next" href="log2.html" title="Compile Time log2 Calculation"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="mod_inverse.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="log2.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 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"><boost/integer/integer_mask.hpp></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"><</span><span class="identifier">cstddef</span><span class="special">></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"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">Bit</span><span class="special">></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"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">Bits</span><span class="special">></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 2. 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 3. 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"><</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">></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"><</span><span class="number">29</span><span class="special">></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"><</span><span class="number">15</span><span class="special">></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">&=</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 © 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> 375<hr> 376<div class="spirit-nav"> 377<a accesskey="p" href="mod_inverse.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="log2.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 378</div> 379</body> 380</html> 381
