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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="math_toolkit.specified_typedefs"></a><a class="link" href="specified_typedefs.html" title="Overview">Overview</a>
  28 </h2></div></div></div>
  29 <p>
  30       The header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">cstdfloat</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
  31       provides <span class="bold"><strong>optional</strong></span> standardized floating-point
  32       <code class="computeroutput"><span class="keyword">typedef</span></code>s having <span class="bold"><strong>specified
  33       widths</strong></span>. These are useful for writing portable code because they
  34       should behave identically on all platforms. These <code class="computeroutput"><span class="keyword">typedef</span></code>s
  35       are the floating-point analog of specified-width integers in <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">cstdint</span><span class="special">&gt;</span></code> and <code class="computeroutput"><span class="identifier">stdint</span><span class="special">.</span><span class="identifier">h</span></code>.
  36     </p>
  37 <p>
  38       The <code class="computeroutput"><span class="keyword">typedef</span></code>s are based on <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3626.pdf" target="_top">N3626</a>
  39       proposed for a new C++14 standard header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">cstdfloat</span><span class="special">&gt;</span></code>
  40       and <a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1703.pdf" target="_top">N1703</a>
  41       proposed for a new C language standard header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">stdfloat</span><span class="special">.</span><span class="identifier">h</span><span class="special">&gt;</span></code>.
  42     </p>
  43 <p>
  44       All <code class="computeroutput"><span class="keyword">typedef</span></code>s are in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">boost</span></code>
  45       (would be in namespace <code class="computeroutput"><span class="identifier">std</span></code>
  46       if eventually standardized).
  47     </p>
  48 <p>
  49       The <code class="computeroutput"><span class="keyword">typedef</span></code>s include <code class="computeroutput"><span class="identifier">float16_t</span><span class="special">,</span> <span class="identifier">float32_t</span><span class="special">,</span> <span class="identifier">float64_t</span><span class="special">,</span> <span class="identifier">float80_t</span><span class="special">,</span> <span class="identifier">float128_t</span></code>, their corresponding least and
  50       fast types, and the corresponding maximum-width type. The <code class="computeroutput"><span class="keyword">typedef</span></code>s
  51       are based on underlying built-in types such as <code class="computeroutput"><span class="keyword">float</span></code>,
  52       <code class="computeroutput"><span class="keyword">double</span></code>, or <code class="computeroutput"><span class="keyword">long</span>
  53       <span class="keyword">double</span></code>, or the proposed <a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2016.pdf" target="_top">N2016
  54       short float type</a>, or based on other compiler-specific non-standardized
  55       types such as <code class="computeroutput"><span class="identifier">__float128</span></code>. The
  56       underlying types of these <code class="computeroutput"><span class="keyword">typedef</span></code>s
  57       must conform with the corresponding specifications of binary16, binary32, binary64,
  58       and binary128 in <a href="http://en.wikipedia.org/wiki/IEEE_floating_point" target="_top">IEEE_floating_point</a>
  59       floating-point format, and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special">&lt;&gt;::</span><span class="identifier">is_iec559</span>
  60       <span class="special">==</span> <span class="keyword">true</span></code>.
  61     </p>
  62 <p>
  63       The 128-bit floating-point type (of great interest in scientific and numeric
  64       programming) is not required in the Boost header, and may not be supplied for
  65       all platforms/compilers, because compiler support for a 128-bit floating-point
  66       type is not mandated by either the C standard or the C++ standard.
  67     </p>
  68 <p>
  69       If 128-bit floating-point is supported, then including <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">cstdfloat</span><span class="special">.</span><span class="identifier">hpp</span></code> provides
  70       a <span class="bold"><strong>native</strong></span> 128-bit type, and includes other
  71       headers in folder <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">cstdfloat</span></code>
  72       that provide C++ quad support for <a href="http://www.cplusplus.com/reference/cmath/" target="_top">C
  73       math functions</a> in <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">cmath</span><span class="special">&gt;</span></code>,
  74       <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">limits</span><span class="special">&gt;</span></code>, <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span></code>,
  75       <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">complex</span><span class="special">&gt;</span></code>, and the available floating-point types.
  76     </p>
  77 <p>
  78       One can also, more robustly, include <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">float128</span><span class="special">.</span><span class="identifier">hpp</span></code> and
  79       this provides a thin wrapper selecting the appropriate 128-bit native type
  80       from <code class="computeroutput"><span class="identifier">cstdfloat</span></code> if available,
  81       or else a 128-bit multiprecision type.
  82     </p>
  83 <p>
  84       See <a class="link" href="examples.html#math_toolkit.examples.je_lambda">Jahnke-Emden-Lambda function
  85       example</a> for an example using both a <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">cmath</span><span class="special">&gt;</span></code>
  86       function and a Boost.Math function to evaluate a moderately interesting function,
  87       the <a href="http://mathworld.wolfram.com/LambdaFunction.html" target="_top">Jahnke-Emden-Lambda
  88       function</a> and <a class="link" href="examples.html#math_toolkit.examples.normal_table">normal
  89       distribution</a> as an example of a statistical distribution from Boost.Math.
  90     </p>
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