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26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | |
27 | <a name="math_toolkit.greatest_typdefs"></a><a class="link" href="greatest_typdefs.html" title="Greatest-width floating-point typedef">Greatest-width floating-point | |
28 | typedef</a> | |
29 | </h2></div></div></div> | |
30 | <p> | |
31 | The <code class="computeroutput"><span class="keyword">typedef</span> <span class="identifier">floatmax_t</span></code> | |
32 | designates a floating-point type capable of representing any value of any floating-point | |
33 | type in a given platform most precisely. | |
34 | </p> | |
35 | <p> | |
36 | The greatest-width <code class="computeroutput"><span class="keyword">typedef</span></code> is | |
37 | provided for all platforms, but, of course, the size may vary. | |
38 | </p> | |
39 | <p> | |
40 | To provide floating-point <span class="bold"><strong>constants</strong></span> most precisely | |
41 | representable for a <code class="computeroutput"><span class="identifier">floatmax_t</span></code> | |
42 | type, use the macro <code class="computeroutput"><span class="identifier">BOOST_FLOATMAX_C</span></code>. | |
43 | </p> | |
44 | <p> | |
45 | For example, replace a constant <code class="computeroutput"><span class="number">123.4567890123456789012345678901234567890</span></code> | |
46 | with | |
47 | </p> | |
48 | <pre class="programlisting"><span class="identifier">BOOST_FLOATMAX_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> | |
49 | </pre> | |
50 | <p> | |
51 | If, for example, <code class="computeroutput"><span class="identifier">floatmax_t</span></code> | |
52 | is <code class="computeroutput"><span class="identifier">float64_t</span></code> then the result | |
53 | will be equivalent to a <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">double</span></code> suffixed with L, but if <code class="computeroutput"><span class="identifier">floatmax_t</span></code> is <code class="computeroutput"><span class="identifier">float128_t</span></code> | |
54 | then the result will be equivalent to a <code class="computeroutput"><span class="identifier">quad</span> | |
55 | <span class="identifier">type</span></code> suffixed with Q (assuming, of | |
56 | course, that <code class="computeroutput"><span class="identifier">float128_t</span></code> (<code class="computeroutput"><span class="identifier">__float128</span></code> or <code class="computeroutput"><span class="identifier">Quad</span></code>) | |
57 | is supported). | |
58 | </p> | |
59 | <p> | |
60 | If we display with <code class="computeroutput"><span class="identifier">max_digits10</span></code>, | |
61 | the maximum possibly significant decimal digits: | |
62 | </p> | |
63 | <pre class="programlisting"><span class="preprocessor">#ifdef</span> <span class="identifier">BOOST_FLOAT32_C</span> | |
64 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">.</span><span class="identifier">precision</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">max_digits10</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">float32_t</span><span class="special">>());</span> <span class="comment">// Show all significant decimal digits,</span> | |
65 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span class="special">.</span><span class="identifier">setf</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios</span><span class="special">::</span><span class="identifier">showpoint</span><span class="special">);</span> <span class="comment">// including all significant trailing zeros.</span> | |
66 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"BOOST_FLOAT32_C(123.4567890123456789012345678901234567890) = "</span> | |
67 | <span class="special"><<</span> <span class="identifier">BOOST_FLOAT32_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> | |
68 | <span class="comment">// BOOST_FLOAT32_C(123.4567890123456789012345678901234567890) = 123.456787</span> | |
69 | <span class="preprocessor">#endif</span> | |
70 | </pre> | |
71 | <p> | |
72 | then on a 128-bit platform (GCC 4.8.1 or higher with quadmath): | |
73 | </p> | |
74 | <pre class="programlisting"><span class="identifier">BOOST_FLOAT32_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.456787</span> | |
75 | <span class="identifier">BOOST_FLOAT64_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.45678901234568</span> | |
76 | <span class="identifier">BOOST_FLOAT80_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.456789012345678903</span> | |
77 | <span class="identifier">BOOST_FLOAT128_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span> <span class="special">=</span> <span class="number">123.456789012345678901234567890123453</span> | |
78 | </pre> | |
79 | </div> | |
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83 | Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert | |
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85 | Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p> | |
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