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4 | <title>Hints on using float128 (and __float128)</title> | |
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26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | |
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> | |
90 | </div> | |
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