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  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_idm46048204416688.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__idm46048203222928.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>&#119926;(N * (log2(range)/s + s))</em></span>, so <code class="literal"><code class="computeroutput"><a class="link" href="../../../../boost/sort/spreadsort/float_so_idm46048204416688.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>&#119926;(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">&amp;</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">&lt;</span><span class="identifier">KEY_TYPE</span><span class="special">,</span> <span class="identifier">CAST_TYPE</span><span class="special">&gt;(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">key</span><span class="special">)</span> <span class="special">&gt;&gt;</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&lt;</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">&amp;</span><span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">DATA_TYPE</span> <span class="special">&amp;</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">&lt;</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>
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 124 <td align="right"><div class="copyright-footer">Copyright &#169; 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>.
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