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[SVN r11972]
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211
doc/integer_mask.html
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doc/integer_mask.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<html>
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<head>
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<title>Integer Bit Mask Templates</title>
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</head>
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<body bgcolor="white" text="black" link="blue" vlink="purple" alink="red">
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<h1><img src="../../../c++boost.gif" alt="c++boost.gif (8819 bytes)"
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align="middle" width="277" height="86">Integer Bit Mask Templates</h1>
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<p>The class templates in <cite><a href="../../../boost/integer/integer_mask.hpp"><boost/integer/integer_mask.hpp></a></cite> 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 href="../integer.htm">integer type selection templates</a> header.</p>
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<h2><a name="contents">Contents</a></h2>
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<ul>
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<li><a href="#contents">Contents</a></li>
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<li><a href="#synopsis">Synopsis</a></li>
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<li><a href="#single">Single Bit-Mask Class Template</a></li>
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<li><a href="#group">Group Bit-Mask Class Template</a></li>
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<li><a href="#example">Example</a></li>
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<li><a href="#demo">Demonstration Program</a></li>
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<li><a href="#rationale">Rationale</a></li>
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<li><a href="#credits">Credits</a></li>
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</ul>
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<h2><a name="synopsis">Synopsis</a></h2>
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<blockquote><pre>
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#include <cstddef> <i>// for std::size_t</i>
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namespace boost
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{
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template < std::size_t Bit >
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struct high_bit_mask_t
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{
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typedef <em>implementation_supplied</em> least;
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typedef <em>implementation_supplied</em> fast;
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static const least high_bit = <em>implementation_defined</em>;
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static const fast high_bit_fast = <em>implementation_defined</em>;
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static const std::size_t bit_position = Bit;
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};
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template < std::size_t Bits >
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struct low_bits_mask_t
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{
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typedef <em>implementation_supplied</em> least;
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typedef <em>implementation_supplied</em> fast;
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static const least sig_bits = <em>implementation_defined</em>;
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static const fast sig_bits_fast = <em>implementation_defined</em>;
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static const std::size_t bit_count = Bits;
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};
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// Specializations for low_bits_mask_t exist for certain bit counts.
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} // namespace boost
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</pre></blockquote>
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<h2><a name="single">Single Bit-Mask Class Template</a></h2>
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<p>The <code>boost::high_bit_mask_t</code> class template provides
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constants for bit masks representing the bit at a certain position. The
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masks are equivalent to the value 2<sup><code>Bit</code></sup>, where
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<code>Bit</code> is the template parameter. The bit position must be a
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nonnegative number from zero to <i>Max</i>, where <dfn>Max</dfn> is one
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less than the number of bits supported by the largest unsigned built-in
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integral type. The following table describes the members of an
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instantiation of <code>high_bit_mask_t</code>.</p>
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<table border="1" cellpadding="5">
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<caption>Members of the <code>boost::high_bit_mask_t</code> Class
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Template</caption>
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<tr>
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<th>Member</th>
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<th>Meaning</th>
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</tr>
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<tr>
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<td><code>least</code></td>
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<td>The smallest unsigned built-in type that supports the given
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bit position.</td>
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</tr>
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<tr>
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<td><code>fast</code></td>
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<td>The quick-to-manipulate analog of <code>least</code>.</td>
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</tr>
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<tr>
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<td><code>high_bit</code></td>
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<td>A <code>least</code> constant of the desired bit-masking
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value.</td>
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</tr>
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<tr>
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<td><code>high_bit_fast</code></td>
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<td>A <code>fast</code> analog of <code>high_bit</code>.</td>
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</tr>
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<tr>
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<td><code>bit_position</code></td>
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<td>The value of the template parameter, in case its needed from
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a renamed instantiation of the class template.</td>
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</tr>
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</table>
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<h2><a name="group">Group Bit-Mask Class Template</a></h2>
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<p>The <code>boost::low_bits_mask_t</code> class template provides
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constants for bit masks representing the lowest bits of a certain
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amount. The masks are equivalent to the value
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(2<sup><code>Bits</code></sup> - 1), where <code>Bits</code> is the
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template parameter. The bit amount must be a nonnegative number from
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zero to <i>Max</i>, where <dfn>Max</dfn> is the number of bits supported
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by the largest unsigned built-in integral type. The following table
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describes the members of an instantiation of
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<code>low_bits_mask_t</code>.</p>
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<table border="1" cellpadding="5">
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<caption>Members of the <code>boost::low_bits_mask_t</code> Class
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Template</caption>
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<tr>
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<th>Member</th>
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<th>Meaning</th>
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</tr>
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<tr>
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<td><code>least</code></td>
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<td>The smallest unsigned built-in type that supports the given
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bit count.</td>
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</tr>
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<tr>
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<td><code>fast</code></td>
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<td>The quick-to-manipulate analog of <code>least</code>.</td>
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</tr>
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<tr>
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<td><code>sig_bits</code></td>
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<td>A <code>least</code> constant of the desired bit-masking
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value.</td>
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</tr>
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<tr>
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<td><code>sig_bits_fast</code></td>
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<td>A <code>fast</code> analog of <code>sig_bits</code>.</td>
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</tr>
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<tr>
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<td><code>bit_count</code></td>
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<td>The value of the template parameter, in case its needed from
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a renamed instantiation of the class template.</td>
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</tr>
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</table>
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<p><strong>Implementation Note</strong><br>
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When <code>Bits</code> is the exact size of a built-in unsigned type,
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the implementation has to change to prevent undefined behavior.
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Therefore, there are specializations of <code>low_bits_mask_t</code> at
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those bit counts.</p>
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<h2><a name="example">Example</a></h2>
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<blockquote><pre>
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#include <boost/integer/integer_mask.hpp>
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//...
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int main()
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{
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typedef boost::high_bit_mask_t<29> mask1_type;
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typedef boost::low_bits_mask_t<15> mask2_type;
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mask1_type::least my_var1;
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mask2_type::fast my_var2;
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//...
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my_var1 |= mask1_type::high_bit;
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my_var2 &= mask2_type::sig_bits_fast;
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//...
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}
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</pre></blockquote>
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<h2><a name="demo">Demonstration Program</a></h2>
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<p>The program <a href="../test/integer_mask_test.cpp">integer_mask_test.cpp</a>
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is a simplistic demonstration of the results from instantiating various
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examples of the bit mask class templates.</p>
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<h2><a name="rationale">Rationale</a></h2>
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<p>The class templates in this header are an extension of the <a
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href="../integer.htm">integer type selection class templates</a>. The new
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class templates provide the same sized types, but also convienent masks
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to use when extracting the highest or all the significant bits when the
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containing built-in type contains more bits. This prevents
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contaimination of values by the higher, unused bits.</p>
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<h2><a name="credits">Credits</a></h2>
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<p>The author of the Boost bit mask class templates is <a
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href="../../../people/daryle_walker.html">Daryle Walker</a>.</p>
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<hr>
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<p>Revised September 23, 2001</p>
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<p>© Copyright Daryle Walker 2001. Permission to copy, use,
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modify, sell and distribute this document is granted provided this
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copyright notice appears in all copies. This document is provided
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"as is" without express or implied warranty, and with no claim
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as to its suitability for any purpose.</p>
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</body>
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</html>
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122
doc/static_log2.html
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122
doc/static_log2.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<html>
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<head>
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<title>Binary Logarithm Template</title>
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</head>
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<body bgcolor="white" text="black">
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<h1><img src="../../../c++boost.gif" alt="c++boost.gif (8819 bytes)"
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align="middle" width="277" height="86">Binary Logarithm Template</h1>
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<p>The class template in <cite><a href="../../../boost/integer/static_log2.hpp"><boost/integer/static_log2.hpp></a></cite> determines the position of the highest bit in a given value. This facility is useful for solving generic programming problems.</p>
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<h2><a name="contents">Contents</a></h2>
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<ul>
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<li><a href="#contents">Contents</a></li>
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<li><a href="#synopsis">Synopsis</a></li>
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<li><a href="#usage">Usage</a></li>
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<li><a href="#example">Example</a></li>
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<li><a href="#demo">Demonstration Program</a></li>
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<li><a href="#rationale">Rationale</a></li>
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<li><a href="#credits">Credits</a></li>
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</ul>
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<h2><a name="synopsis">Synopsis</a></h2>
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<blockquote><pre>
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namespace boost
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{
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template < unsigned long Value >
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struct static_log2
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{
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static const int value = <em>implementation_defined</em>;
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};
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template < >
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struct static_log2< 0ul >
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{
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// The logarithm of zero is undefined.
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};
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} // namespace boost
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</pre></blockquote>
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<h2><a name="usage">Usage</a></h2>
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<p>The <code>boost::static_log2</code> class template takes one template
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parameter, a value of type <code>unsigned long</code>. The template
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only defines one member, <code>value</code>, that returns the truncated
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base-two logarithm of the template parameter.</p>
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<p>Since the logarithm of zero, for any base, is undefined, there is a
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specialization of <code>static_log2</code> for a template parameter
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of zero. This specialization has no members, so an attempt to use
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the base-two logarithm of zero results in a compile-time error.</p>
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<h2><a name="example">Example</a></h2>
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<blockquote><pre>
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#include <boost/integer/static_log2.hpp>
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template < unsigned long Value >
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bool is_it_what()
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{
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typedef boost::static_log2<Value> lb_type;
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int temp = lb_type::value;
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//...
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return (temp % 2) != 0;
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}
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//...
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int main()
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{
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bool temp = is_it_what<2000>();
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//...
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#if 0
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temp = is_it_what<0>(); // would give an error
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#endif
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//...
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temp = is_it_what<24>();
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//...
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}
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</pre></blockquote>
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<h2><a name="demo">Demonstration Program</a></h2>
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<p>The program <a href="../test/static_log2_test.cpp">static_log2_test.cpp</a>
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is a simplistic demonstration of the results from instantiating various
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examples of the binary logarithm class template.</p>
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<h2><a name="rationale">Rationale</a></h2>
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<p>The base-two (binary) logarithm, abbreviated <dfn>lb</dfn>, function
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is occasionally used to give order-estimates of computer algorithms.
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The truncated logarithm can be considered the highest power-of-two in a
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value, which corresponds to the value's highest set bit (for binary
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integers). Sometimes the highest-bit position could be used in generic
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programming, which requires the position to be statically (<i>i.e.</i>
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at compile-time) available.</p>
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<h2><a name="credits">Credits</a></h2>
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<p>The author of the Boost binary logarithm class template is <a
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href="../../../people/daryle_walker.html">Daryle Walker</a>.</p>
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<hr>
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<p>Revised October 1, 2001</p>
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||||
<p>© Copyright Daryle Walker 2001. Permission to copy, use,
|
||||
modify, sell and distribute this document is granted provided this
|
||||
copyright notice appears in all copies. This document is provided
|
||||
"as is" without express or implied warranty, and with no claim
|
||||
as to its suitability for any purpose.</p>
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</body>
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</html>
|
121
doc/static_min_max.html
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121
doc/static_min_max.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<html>
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<head>
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<title>Compile-Time Extrema Templates</title>
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</head>
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<body bgcolor="white" text="black" link="blue" alink="red" vlink="purple">
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<h1><img src="../../../c++boost.gif" alt="c++boost.gif (8819 bytes)"
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align="middle" width="277" height="86">Compile-Time Extrema
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Templates</h1>
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<p>The class templates in <cite><a
|
||||
href="../../../boost/integer/static_min_max.hpp"><boost/integer/static_min_max.hpp></a></cite>
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||||
provide a compile-time evaluation of the minimum or maximum of
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two integers. These facilities are useful for generic programming problems.</p>
|
||||
|
||||
<h2><a name="contents">Contents</a></h2>
|
||||
|
||||
<ul>
|
||||
<li><a href="#contents">Contents</a></li>
|
||||
<li><a href="#synopsis">Synopsis</a></li>
|
||||
<li><a href="#usage">Usage</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="#credits">Credits</a></li>
|
||||
</ul>
|
||||
|
||||
<h2><a name="synopsis">Synopsis</a></h2>
|
||||
|
||||
<blockquote><pre>
|
||||
namespace boost
|
||||
{
|
||||
|
||||
template < long Value1, long Value2 >
|
||||
struct static_signed_min;
|
||||
|
||||
template < long Value1, long Value2 >
|
||||
struct static_signed_max;
|
||||
|
||||
template < unsigned long Value1, unsigned long Value2 >
|
||||
struct static_unsigned_min;
|
||||
|
||||
template < unsigned long Value1, unsigned long Value2 >
|
||||
struct static_unsigned_max;
|
||||
|
||||
}
|
||||
</pre></blockquote>
|
||||
|
||||
<h2><a name="usage">Usage</a></h2>
|
||||
|
||||
<p>The four class templates provide the combinations for finding the
|
||||
minimum or maximum of two signed or <code>unsigned</code>
|
||||
(<code>long</code>) parameters, <var>Value1</var> and <var>Value2</var>,
|
||||
at compile-time. Each template has a single static data member,
|
||||
<code>value</code>, which is set to the respective minimum or maximum
|
||||
of the template's parameters.</p>
|
||||
|
||||
<h2><a name="example">Example</a></h2>
|
||||
|
||||
<blockquote><pre>
|
||||
#include <boost/integer/static_min_max.hpp>
|
||||
|
||||
template < unsigned long AddendSize1, unsigned long AddendSize2 >
|
||||
class adder
|
||||
{
|
||||
public:
|
||||
static unsigned long const addend1_size = AddendSize1;
|
||||
static unsigned long const addend2_size = AddendSize2;
|
||||
static unsigned long const sum_size = boost::static_unsigned_max<AddendSize1, AddendSize2>::value + 1;
|
||||
|
||||
typedef int addend1_type[ addend1_size ];
|
||||
typedef int addend2_type[ addend2_size ];
|
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typedef int sum_type[ sum_size ];
|
||||
|
||||
void operator ()( addend1_type const &a1, addend2_type const &a2, sum_type &s ) const;
|
||||
};
|
||||
|
||||
//...
|
||||
|
||||
int main()
|
||||
{
|
||||
int const a1[] = { 0, 4, 3 }; // 340
|
||||
int const a2[] = { 9, 8 }; // 89
|
||||
int s[ 4 ];
|
||||
adder<3,2> obj;
|
||||
|
||||
obj( a1, a2, s ); // 's' should be 429 or { 9, 2, 4, 0 }
|
||||
//...
|
||||
}
|
||||
</pre></blockquote>
|
||||
|
||||
<h2><a name="demo">Demonstration Program</a></h2>
|
||||
|
||||
<p>The program <a
|
||||
href="../test/static_min_max_test.cpp">static_min_max_test.cpp</a> is a
|
||||
simplistic demonstration of various comparisons using the compile-time
|
||||
extrema class templates.</p>
|
||||
|
||||
<h2><a name="rationale">Rationale</a></h2>
|
||||
|
||||
<p>Sometimes the minimum or maximum of several values needs to be found
|
||||
for later compile-time processing, <i>e.g.</i> for a bound for another
|
||||
class template.</p>
|
||||
|
||||
<h2><a name="credits">Credits</a></h2>
|
||||
|
||||
<p>The author of the Boost compile-time extrema class templates is <a
|
||||
href="../../../../people/daryle_walker.html">Daryle Walker</a>.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<p>Revised October 12, 2001</p>
|
||||
|
||||
<p>© Copyright Daryle Walker 2001. Permission to copy, use,
|
||||
modify, sell and distribute this document is granted provided this
|
||||
copyright notice appears in all copies. This document is provided
|
||||
"as is" without express or implied warranty, and with no claim
|
||||
as to its suitability for any purpose.</p>
|
||||
</body>
|
||||
</html>
|
Reference in New Issue
Block a user