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  27 <a name="math_toolkit.float128_hints"></a><a class="link" href="float128_hints.html" title="Hints on using float128 (and __float128)">Hints on using float128 (and
  28     __float128)</a>
  29 </h2></div></div></div>
  30 <h6>
  31 <a name="math_toolkit.float128_hints.h0"></a>
  32       <span class="phrase"><a name="math_toolkit.float128_hints.different_float128"></a></span><a class="link" href="float128_hints.html#math_toolkit.float128_hints.different_float128">__float128
  33       versus float128</a>
  34     </h6>
  35 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  36 <li class="listitem">
  37           __float128 is the (optionally) compiler supplied hardware type, it's an
  38           C-ish extension to C++ and there is only minimal support for it in normal
  39           C++ (no IO streams or <code class="computeroutput"><span class="identifier">numeric_limits</span></code>
  40           support, function names in libquadmath all have different names to the
  41           <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span></code>
  42           ones etc.) So you can program type <code class="computeroutput"><span class="identifier">__float128</span></code>
  43           directly, but it's harder work.
  44         </li>
  45 <li class="listitem">
  46           Type <code class="computeroutput"><span class="identifier">float128</span></code> uses __float128
  47           and makes it C++ and generic code friendly, with all the usual standard
  48           <code class="computeroutput"><span class="identifier">iostream</span></code>, <code class="computeroutput"><span class="identifier">numeric_limits</span></code>, <code class="computeroutput"><span class="identifier">complex</span></code>
  49           in namspace <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span></code>
  50           available, so strongly recommended for C++ use.
  51         </li>
  52 </ul></div>
  53 <h6>
  54 <a name="math_toolkit.float128_hints.h1"></a>
  55       <span class="phrase"><a name="math_toolkit.float128_hints.hints_and_tips"></a></span><a class="link" href="float128_hints.html#math_toolkit.float128_hints.hints_and_tips">Hints
  56       and tips</a>
  57     </h6>
  58 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  59 <li class="listitem">
  60           Make sure you declare variables with the correct type, here <code class="computeroutput"><span class="identifier">float128</span></code>.
  61         </li>
  62 <li class="listitem">
  63           Make sure that if you pass a variable to a function then it is casted to
  64           <code class="computeroutput"><span class="identifier">float128</span></code>.
  65         </li>
  66 <li class="listitem">
  67           Make sure you declare literals with the correct suffix - otherwise they'll
  68           be treated as type <code class="computeroutput"><span class="keyword">double</span></code>
  69           with catastrophic loss of precision. So make sure they have a Q suffix
  70           for 128-bit floating-point literals.
  71         </li>
  72 <li class="listitem">
  73           All the std library functions, cmath functions, plus all the constants,
  74           and special functions from Boost.Math should then just work.
  75         </li>
  76 <li class="listitem">
  77           Make sure std lib functions are called <span class="bold"><strong>unqualified</strong></span>
  78           so that the correct overload is found via <a href="http://en.cppreference.com/w/cpp/language/adl" target="_top">Argument
  79           Dependent Lookup (ADL)</a>. So write sqrt(variable) and not std::sqrt(variable).
  80         </li>
  81 <li class="listitem">
  82           In general, try not to reinvent stuff - using constants from Boost.Math
  83           is probably less error prone than declaring your own, likewise the special
  84           functions etc.
  85         </li>
  86 </ul></div>
  87 <p>
  88       Some examples of what can go horribly and silently wrong are at <a href="../../../example/float128_example.cpp" target="_top">float128_example.cpp</a>.
  89     </p>
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  95       Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan
  96       R&#229;de, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg,
  97       Daryle Walker and Xiaogang Zhang<p>
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