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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="boost_multiprecision.tut.ints.gmp_int"></a><a class="link" href="gmp_int.html" title="gmp_int">gmp_int</a>
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</h4></div></div></div>
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<p>
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<code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">gmp</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
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</p>
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<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">multiprecision</span><span class="special">{</span>
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<span class="keyword">class</span> <span class="identifier">gmp_int</span><span class="special">;</span>
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<span class="keyword">typedef</span> <span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_int</span> <span class="special">></span> <span class="identifier">mpz_int</span><span class="special">;</span>
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<span class="special">}}</span> <span class="comment">// namespaces</span>
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</pre>
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<p>
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The <code class="computeroutput"><span class="identifier">gmp_int</span></code> back-end is
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used via the typedef <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">mpz_int</span></code>.
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It acts as a thin wrapper around the <a href="http://gmplib.org" target="_top">GMP</a>
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<code class="computeroutput"><span class="identifier">mpz_t</span></code> to provide an integer
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type that is a drop-in replacement for the native C++ integer types, but
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with unlimited precision.
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</p>
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<p>
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As well as the usual conversions from arithmetic and string types, type
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<code class="computeroutput"><span class="identifier">mpz_int</span></code> is copy constructible
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and assignable from:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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The <a href="http://gmplib.org" target="_top">GMP</a> native types: <code class="computeroutput"><span class="identifier">mpf_t</span></code>, <code class="computeroutput"><span class="identifier">mpz_t</span></code>,
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<code class="computeroutput"><span class="identifier">mpq_t</span></code>.
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</li>
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<li class="listitem">
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Instances of <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> that are wrappers around those
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types: <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_float</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">></span></code>, <code class="computeroutput"><span class="identifier">number</span><span class="special"><</span><span class="identifier">gmp_rational</span><span class="special">></span></code>.
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</li>
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</ul></div>
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<p>
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It's also possible to access the underlying <code class="computeroutput"><span class="identifier">mpz_t</span></code>
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via the <code class="computeroutput"><span class="identifier">data</span><span class="special">()</span></code>
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member function of <code class="computeroutput"><span class="identifier">gmp_int</span></code>.
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</p>
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<p>
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Things you should know when using this type:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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No changes are made to the GMP library's global settings - so you can
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safely mix this type with existing code that uses <a href="http://gmplib.org" target="_top">GMP</a>.
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</li>
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<li class="listitem">
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Default constructed <code class="computeroutput"><span class="identifier">gmp_int</span></code>s
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have the value zero (this is GMP's default behavior).
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</li>
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<li class="listitem">
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Formatted IO for this type does not support octal or hexadecimal notation
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for negative values, as a result performing formatted output on this
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type when the argument is negative and either of the flags <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">oct</span></code> or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">hex</span></code>
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are set, will result in a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span></code>
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will be thrown.
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</li>
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<li class="listitem">
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Conversion from a string results in a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">runtime_error</span></code>
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being thrown if the string can not be interpreted as a valid integer.
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</li>
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<li class="listitem">
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Division by zero results in a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">overflow_error</span></code>
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being thrown.
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</li>
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<li class="listitem">
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Although this type is a wrapper around <a href="http://gmplib.org" target="_top">GMP</a>
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it will work equally well with <a href="http://mpir.org/" target="_top">MPIR</a>.
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Indeed use of <a href="http://mpir.org/" target="_top">MPIR</a> is recommended
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on Win32.
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</li>
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<li class="listitem">
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This backend supports rvalue-references and is move-aware, making instantiations
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of <code class="computeroutput"><span class="identifier">number</span></code> on this backend
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move aware.
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</li>
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</ul></div>
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<h6>
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<a name="boost_multiprecision.tut.ints.gmp_int.h0"></a>
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<span class="phrase"><a name="boost_multiprecision.tut.ints.gmp_int.example"></a></span><a class="link" href="gmp_int.html#boost_multiprecision.tut.ints.gmp_int.example">Example:</a>
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</h6>
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<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">gmp</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span>
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<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
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<span class="special">{</span>
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<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">;</span>
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<span class="identifier">mpz_int</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
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<span class="comment">// Do some arithmetic:</span>
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<span class="keyword">for</span><span class="special">(</span><span class="keyword">unsigned</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><=</span> <span class="number">1000</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span>
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<span class="identifier">v</span> <span class="special">*=</span> <span class="identifier">i</span><span class="special">;</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">v</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> <span class="comment">// prints 1000!</span>
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<span class="comment">// Access the underlying representation:</span>
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<span class="identifier">mpz_t</span> <span class="identifier">z</span><span class="special">;</span>
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<span class="identifier">mpz_init</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
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<span class="identifier">mpz_set</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">backend</span><span class="special">().</span><span class="identifier">data</span><span class="special">());</span>
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<span class="identifier">mpz_clear</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
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<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
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<span class="special">}</span>
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</pre>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2002-2019 John Maddock
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and Christopher Kormanyos<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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