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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="math_toolkit.greatest_typdefs"></a><a class="link" href="greatest_typdefs.html" title="Greatest-width floating-point typedef">Greatest-width floating-point
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typedef</a>
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</h2></div></div></div>
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<p>
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The <code class="computeroutput"><span class="keyword">typedef</span> <span class="identifier">floatmax_t</span></code>
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designates a floating-point type capable of representing any value of any floating-point
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type in a given platform most precisely.
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The greatest-width <code class="computeroutput"><span class="keyword">typedef</span></code> is
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provided for all platforms, but, of course, the size may vary.
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<p>
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To provide floating-point <span class="bold"><strong>constants</strong></span> most precisely
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representable for a <code class="computeroutput"><span class="identifier">floatmax_t</span></code>
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type, use the macro <code class="computeroutput"><span class="identifier">BOOST_FLOATMAX_C</span></code>.
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</p>
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<p>
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For example, replace a constant <code class="computeroutput"><span class="number">123.4567890123456789012345678901234567890</span></code>
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with
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</p>
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<pre class="programlisting"><span class="identifier">BOOST_FLOATMAX_C</span><span class="special">(</span><span class="number">123.4567890123456789012345678901234567890</span><span class="special">)</span>
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</pre>
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<p>
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If, for example, <code class="computeroutput"><span class="identifier">floatmax_t</span></code>
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is <code class="computeroutput"><span class="identifier">float64_t</span></code> then the result
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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>
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then the result will be equivalent to a <code class="computeroutput"><span class="identifier">quad</span>
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<span class="identifier">type</span></code> suffixed with Q (assuming, of
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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>)
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is supported).
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</p>
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<p>
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If we display with <code class="computeroutput"><span class="identifier">max_digits10</span></code>,
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the maximum possibly significant decimal digits:
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</p>
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<pre class="programlisting"><span class="preprocessor">#ifdef</span> <span class="identifier">BOOST_FLOAT32_C</span>
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<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>
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<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>
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<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>
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<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>
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<span class="comment">// BOOST_FLOAT32_C(123.4567890123456789012345678901234567890) = 123.456787</span>
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<span class="preprocessor">#endif</span>
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</pre>
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<p>
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then on a 128-bit platform (GCC 4.8.1 or higher with quadmath):
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</p>
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<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>
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<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>
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<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>
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<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>
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</pre>
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