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- <div class="titlepage"><div><div><h2 class="title" style="clear: both">
- <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
- __float128)</a>
- </h2></div></div></div>
- <h6>
- <a name="math_toolkit.float128_hints.h0"></a>
- <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
- versus float128</a>
- </h6>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- __float128 is the (optionally) compiler supplied hardware type, it's an
- C-ish extension to C++ and there is only minimal support for it in normal
- C++ (no IO streams or <code class="computeroutput"><span class="identifier">numeric_limits</span></code>
- support, function names in libquadmath all have different names to the
- <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span></code>
- ones etc.) So you can program type <code class="computeroutput"><span class="identifier">__float128</span></code>
- directly, but it's harder work.
- </li>
- <li class="listitem">
- Type <code class="computeroutput"><span class="identifier">float128</span></code> uses __float128
- and makes it C++ and generic code friendly, with all the usual standard
- <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>
- in namspace <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span></code>
- available, so strongly recommended for C++ use.
- </li>
- </ul></div>
- <h6>
- <a name="math_toolkit.float128_hints.h1"></a>
- <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
- and tips</a>
- </h6>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- Make sure you declare variables with the correct type, here <code class="computeroutput"><span class="identifier">float128</span></code>.
- </li>
- <li class="listitem">
- Make sure that if you pass a variable to a function then it is casted to
- <code class="computeroutput"><span class="identifier">float128</span></code>.
- </li>
- <li class="listitem">
- Make sure you declare literals with the correct suffix - otherwise they'll
- be treated as type <code class="computeroutput"><span class="keyword">double</span></code>
- with catastrophic loss of precision. So make sure they have a Q suffix
- for 128-bit floating-point literals.
- </li>
- <li class="listitem">
- All the std library functions, cmath functions, plus all the constants,
- and special functions from Boost.Math should then just work.
- </li>
- <li class="listitem">
- Make sure std lib functions are called <span class="bold"><strong>unqualified</strong></span>
- so that the correct overload is found via <a href="http://en.cppreference.com/w/cpp/language/adl" target="_top">Argument
- Dependent Lookup (ADL)</a>. So write sqrt(variable) and not std::sqrt(variable).
- </li>
- <li class="listitem">
- In general, try not to reinvent stuff - using constants from Boost.Math
- is probably less error prone than declaring your own, likewise the special
- functions etc.
- </li>
- </ul></div>
- <p>
- Some examples of what can go horribly and silently wrong are at <a href="../../../example/float128_example.cpp" target="_top">float128_example.cpp</a>.
- </p>
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