1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Float Sort</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.Sort"> 8<link rel="up" href="../sort_hpp.html" title="Spreadsort"> 9<link rel="prev" href="integer_sort.html" title="Integer Sort"> 10<link rel="next" href="string_sort.html" title="String Sort"> 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="integer_sort.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../sort_hpp.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="string_sort.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="sort.single_thread.spreadsort.sort_hpp.float_sort"></a><a class="link" href="float_sort.html" title="Float Sort">Float 28 Sort</a> 29</h5></div></div></div> 30<p> 31 <code class="literal"><code class="computeroutput"><a class="link" href="../../../../boost/sort/spreadsort/float_so_idm45878545215024.html" title="Function template float_sort">float_sort</a></code></code> 32 is a fast templated in-place hybrid radix/comparison algorithm much like 33 <code class="literal"><code class="computeroutput"><a class="link" href="../../../../boost/sort/spreadsort/integer__idm45878544022768.html" title="Function template integer_sort">integer_sort</a></code></code>, 34 but sorts IEEE floating-point numbers (positive, zero, NaN, and negative) 35 into ascending order by casting them to integers. This works because 36 positive IEEE floating-point numbers sort like integers with the same 37 bits, and negative IEEE floating-point numbers sort in the reverse order 38 of integers with the same bits. float_sort is roughly 2X as fast as std::sort. 39 </p> 40<p> 41 -0.0 vs. 0.0 and NaN are given definitive ordered positions by the radix-based 42 portion of this algorithm, where comparison-based sorting does not guarantee 43 their relative position. The included tests avoid creating NaN and -0.0 44 so that results match std::sort, which is not consistent in how it handles 45 these numbers, as they compare as equal to numbers with different values. 46 </p> 47<p> 48 float_sort checks the size of the data type and whether it is castable, 49 picking an integer type to cast to, if a casting functor isn't provided 50 by the user. 51 </p> 52<p> 53 float_mem_cast casts IEEE floating-point numbers (positive, zero, NaN, 54 and negative) into integers. This is an essential utility for creating 55 a custom rightshift functor for float_sort, when one is needed. Only 56 IEEE floating-point numbers of the same size as the integer type being 57 cast to should be used in this specialized method call. Worst-case performance 58 is <span class="emphasis"><em>��(N * (log2(range)/s + s))</em></span>, so <code class="literal"><code class="computeroutput"><a class="link" href="../../../../boost/sort/spreadsort/float_so_idm45878545215024.html" title="Function template float_sort">float_sort</a></code></code> 59 is asymptotically faster than pure comparison-based algorithms. <span class="emphasis"><em>s</em></span> 60 is <span class="emphasis"><em>max_splits</em></span>, which defaults to 11, so its worst-case 61 with default settings for 32-bit integers is <span class="emphasis"><em>��(N * ((32/11)</em></span> 62 slow radix-based iterations + 11 fast comparison-based iterations). 63 </p> 64<p> 65 Some performance plots of runtime vs. n and log2(range) are provided 66 below: 67 </p> 68<p> 69 <a href="../../../../../../doc/graph/windows_float_sort.htm" target="_top">Windows Float Sort</a> 70 </p> 71<p> 72 <a href="../../../../../../doc/graph/osx_float_sort.htm" target="_top">OSX Float Sort</a> 73 </p> 74<div class="section"> 75<div class="titlepage"><div><div><h6 class="title"> 76<a name="sort.single_thread.spreadsort.sort_hpp.float_sort.floatsort_examples"></a><a class="link" href="float_sort.html#sort.single_thread.spreadsort.sort_hpp.float_sort.floatsort_examples" title="Float Sort Examples">Float 77 Sort Examples</a> 78</h6></div></div></div> 79<p> 80 See <a href="../../../../../../example/floatfunctorsample.cpp" target="_top">floatfunctorsample.cpp</a> 81 for a working example of how to sort structs with a float key: 82 </p> 83<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">CAST_TYPE</span> <span class="keyword">int</span> 84<span class="preprocessor">#define</span> <span class="identifier">KEY_TYPE</span> <span class="keyword">float</span> 85</pre> 86<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">DATA_TYPE</span> <span class="special">{</span> 87 <span class="identifier">KEY_TYPE</span> <span class="identifier">key</span><span class="special">;</span> 88 <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">data</span><span class="special">;</span> 89<span class="special">};</span> 90</pre> 91<p> 92 Right-shift functor: 93 </p> 94<pre class="programlisting"><span class="comment">// Casting to an integer before bitshifting</span> 95<span class="keyword">struct</span> <span class="identifier">rightshift</span> <span class="special">{</span> 96 <span class="keyword">int</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&</span><span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">unsigned</span> <span class="identifier">offset</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> 97 <span class="keyword">return</span> <span class="identifier">float_mem_cast</span><span class="special"><</span><span class="identifier">KEY_TYPE</span><span class="special">,</span> <span class="identifier">CAST_TYPE</span><span class="special">>(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">key</span><span class="special">)</span> <span class="special">>></span> <span class="identifier">offset</span><span class="special">;</span> 98 <span class="special">}</span> 99<span class="special">};</span> 100</pre> 101<p> 102 Comparison lessthan <code class="computeroutput">operator<</code> functor: 103 </p> 104<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">lessthan</span> <span class="special">{</span> 105 <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&</span><span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&</span><span class="identifier">y</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> 106 <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">key</span> <span class="special"><</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">key</span><span class="special">;</span> 107 <span class="special">}</span> 108<span class="special">};</span> 109</pre> 110<p> 111 Other examples: 112 </p> 113<p> 114 <a href="../../../../../../example/double.cpp" target="_top">Sort doubles.</a> 115 </p> 116<p> 117 <a href="../../../../../../example/shiftfloatsample.cpp" target="_top">Sort floats using a 118 rightshift functor.</a> 119 </p> 120</div> 121</div> 122<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 123<td align="left"></td> 124<td align="right"><div class="copyright-footer">Copyright © 2014-2017 Steven 125 Ross, Francisco Tapia, Orson Peters<p> 126 Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost 127 Software License, Version 1.0</a>. 128 </p> 129</div></td> 130</tr></table> 131<hr> 132<div class="spirit-nav"> 133<a accesskey="p" href="integer_sort.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../sort_hpp.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="string_sort.html"><img src="../../../../../../../../doc/src/images/next.png" 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