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  4. <title>Importing and Exporting Data to and from cpp_int and cpp_bin_float</title>
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  24. </div>
  25. <div class="section">
  26. <div class="titlepage"><div><div><h3 class="title">
  27. <a name="boost_multiprecision.tut.import_export"></a><a class="link" href="import_export.html" title="Importing and Exporting Data to and from cpp_int and cpp_bin_float">Importing and
  28. Exporting Data to and from <code class="computeroutput"><span class="identifier">cpp_int</span></code>
  29. and <code class="computeroutput"><span class="identifier">cpp_bin_float</span></code></a>
  30. </h3></div></div></div>
  31. <p>
  32. Any integer number type that uses <code class="computeroutput"><span class="identifier">cpp_int_backend</span></code>
  33. as it's implementation layer can import or export its bits via two non-member
  34. functions:
  35. </p>
  36. <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">unsigned</span> <span class="identifier">MinBits</span><span class="special">,</span> <span class="keyword">unsigned</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">cpp_integer_type</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">cpp_int_check_type</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Allocator</span><span class="special">,</span>
  37. <span class="identifier">expression_template_option</span> <span class="identifier">ExpressionTemplates</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">OutputIterator</span><span class="special">&gt;</span>
  38. <span class="identifier">OutputIterator</span> <span class="identifier">export_bits</span><span class="special">(</span>
  39. <span class="keyword">const</span> <span class="identifier">number</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="identifier">cpp_int_backend</span><span class="special">&lt;</span><span class="identifier">MinBits</span><span class="special">,</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;,</span> <span class="identifier">ExpressionTemplates</span><span class="special">&gt;&amp;</span> <span class="identifier">val</span><span class="special">,</span>
  40. <span class="identifier">OutputIterator</span> <span class="identifier">out</span><span class="special">,</span>
  41. <span class="keyword">unsigned</span> <span class="identifier">chunk_size</span><span class="special">,</span>
  42. <span class="keyword">bool</span> <span class="identifier">msv_first</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">);</span>
  43. <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">unsigned</span> <span class="identifier">MinBits</span><span class="special">,</span> <span class="keyword">unsigned</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">cpp_integer_type</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">cpp_int_check_type</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Allocator</span><span class="special">,</span>
  44. <span class="identifier">expression_template_option</span> <span class="identifier">ExpressionTemplates</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
  45. <span class="identifier">number</span><span class="special">&lt;</span><span class="identifier">cpp_int_backend</span><span class="special">&lt;</span><span class="identifier">MinBits</span><span class="special">,</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;,</span> <span class="identifier">ExpressionTemplates</span><span class="special">&gt;&amp;</span>
  46. <span class="identifier">import_bits</span><span class="special">(</span>
  47. <span class="identifier">number</span><span class="special">&lt;</span><span class="identifier">cpp_int_backend</span><span class="special">&lt;</span><span class="identifier">MinBits</span><span class="special">,</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;,</span> <span class="identifier">ExpressionTemplates</span><span class="special">&gt;&amp;</span> <span class="identifier">val</span><span class="special">,</span>
  48. <span class="identifier">Iterator</span> <span class="identifier">i</span><span class="special">,</span>
  49. <span class="identifier">Iterator</span> <span class="identifier">j</span><span class="special">,</span>
  50. <span class="keyword">unsigned</span> <span class="identifier">chunk_size</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span>
  51. <span class="keyword">bool</span> <span class="identifier">msv_first</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">);</span>
  52. </pre>
  53. <p>
  54. These functions are designed for data-interchange with other storage formats,
  55. and since <a class="link" href="floats/cpp_bin_float.html" title="cpp_bin_float">cpp_bin_float</a>
  56. uses <a class="link" href="ints/cpp_int.html" title="cpp_int">cpp_int</a>
  57. internally, by extension they can be used for floating-point numbers based
  58. on that backend as well (see example below). Parameters and use are as follows:
  59. </p>
  60. <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">unsigned</span> <span class="identifier">MinBits</span><span class="special">,</span> <span class="keyword">unsigned</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">cpp_integer_type</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">cpp_int_check_type</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Allocator</span><span class="special">,</span>
  61. <span class="identifier">expression_template_option</span> <span class="identifier">ExpressionTemplates</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">OutputIterator</span><span class="special">&gt;</span>
  62. <span class="identifier">OutputIterator</span> <span class="identifier">export_bits</span><span class="special">(</span>
  63. <span class="keyword">const</span> <span class="identifier">number</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="identifier">cpp_int_backend</span><span class="special">&lt;</span><span class="identifier">MinBits</span><span class="special">,</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;,</span> <span class="identifier">ExpressionTemplates</span><span class="special">&gt;&amp;</span> <span class="identifier">val</span><span class="special">,</span>
  64. <span class="identifier">OutputIterator</span> <span class="identifier">out</span><span class="special">,</span>
  65. <span class="keyword">unsigned</span> <span class="identifier">chunk_size</span><span class="special">,</span>
  66. <span class="keyword">bool</span> <span class="identifier">msv_first</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">);</span>
  67. </pre>
  68. <p>
  69. Exports the absolute value of <code class="computeroutput"><span class="identifier">val</span></code>
  70. to OutputIterator <code class="computeroutput"><span class="identifier">out</span></code>. The
  71. function will write <code class="computeroutput"><span class="identifier">chunk_size</span></code>
  72. bits at a time to the OutputIterator, and if <code class="computeroutput"><span class="identifier">msv_first</span></code>
  73. is true, will write the most-significant block first. Byte and bit order
  74. within each <code class="computeroutput"><span class="identifier">chunk_size</span></code> block
  75. is always in the machines native format. Further, each block is stored in
  76. a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">uintmax_t</span></code> when it's assigned to <code class="computeroutput"><span class="special">*</span><span class="identifier">out</span></code>.
  77. </p>
  78. <div class="note"><table border="0" summary="Note">
  79. <tr>
  80. <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
  81. <th align="left">Note</th>
  82. </tr>
  83. <tr><td align="left" valign="top"><p>
  84. Unfortunately, the standard's OutputIterator concept provides no means
  85. of deducing the type to output since <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">OutputIteratorType</span><span class="special">&gt;::</span><span class="identifier">value_type</span></code>
  86. is type <code class="computeroutput"><span class="keyword">void</span></code>. This is why
  87. the bit count for each block has to be specified manually. It may also
  88. result in compiler warnings about the value being narrowed.
  89. </p></td></tr>
  90. </table></div>
  91. <div class="tip"><table border="0" summary="Tip">
  92. <tr>
  93. <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../../../doc/src/images/tip.png"></td>
  94. <th align="left">Tip</th>
  95. </tr>
  96. <tr><td align="left" valign="top"><p>
  97. If you're exporting to non-native byte layout, then use <a href="http://www.boost.org/doc/libs/release/libs/endian/doc/index.html" target="_top">Boost.Endian</a>
  98. to create a custom OutputIterator that reverses the byte order of each
  99. chunk prior to actually storing the result.
  100. </p></td></tr>
  101. </table></div>
  102. <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">unsigned</span> <span class="identifier">MinBits</span><span class="special">,</span> <span class="keyword">unsigned</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">cpp_integer_type</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">cpp_int_check_type</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Allocator</span><span class="special">,</span>
  103. <span class="identifier">expression_template_option</span> <span class="identifier">ExpressionTemplates</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">ForwardIterator</span><span class="special">&gt;</span>
  104. <span class="identifier">number</span><span class="special">&lt;</span><span class="identifier">cpp_int_backend</span><span class="special">&lt;</span><span class="identifier">MinBits</span><span class="special">,</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;,</span> <span class="identifier">ExpressionTemplates</span><span class="special">&gt;&amp;</span>
  105. <span class="identifier">import_bits</span><span class="special">(</span>
  106. <span class="identifier">number</span><span class="special">&lt;</span><span class="identifier">cpp_int_backend</span><span class="special">&lt;</span><span class="identifier">MinBits</span><span class="special">,</span> <span class="identifier">MaxBits</span><span class="special">,</span> <span class="identifier">SignType</span><span class="special">,</span> <span class="identifier">Checked</span><span class="special">,</span> <span class="identifier">Allocator</span><span class="special">&gt;,</span> <span class="identifier">ExpressionTemplates</span><span class="special">&gt;&amp;</span> <span class="identifier">val</span><span class="special">,</span>
  107. <span class="identifier">ForwardIterator</span> <span class="identifier">i</span><span class="special">,</span>
  108. <span class="identifier">ForwardIterator</span> <span class="identifier">j</span><span class="special">,</span>
  109. <span class="keyword">unsigned</span> <span class="identifier">chunk_size</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span>
  110. <span class="keyword">bool</span> <span class="identifier">msv_first</span> <span class="special">=</span> <span class="keyword">true</span><span class="special">);</span>
  111. </pre>
  112. <p>
  113. Imports bits from the iterator range <span class="emphasis"><em>[i,j)</em></span> and stores
  114. them in <code class="computeroutput"><span class="identifier">val</span></code> to produce an
  115. unsigned result (if the result is to be signed you will need to handle that
  116. separately). When <code class="computeroutput"><span class="identifier">msv_first</span></code>
  117. is true, takes <code class="computeroutput"><span class="special">*</span><span class="identifier">i</span></code>
  118. as the most significant chunk. Assumes there are <code class="computeroutput"><span class="identifier">chunk_size</span></code>
  119. bits in each value read from the iterator range, and that these are in machine
  120. native bit/byte order. When <code class="computeroutput"><span class="identifier">chunk_size</span></code>
  121. is zero, then assumes that each chunk contains <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">ForwardIterator</span><span class="special">&gt;::</span><span class="identifier">value_type</span><span class="special">&gt;::</span><span class="identifier">digits</span></code>,
  122. note that this will give the wrong result if dereferencing the iterators
  123. leads to a signed-integer type, <span class="bold"><strong>and</strong></span> the
  124. sign bit is significant (be particularly careful if you expect type <code class="computeroutput"><span class="keyword">char</span></code> to contain 8-bit values, as by default
  125. it will extract only 7-bits at a time if <code class="computeroutput"><span class="keyword">char</span></code>
  126. is signed). As with exporting, if the external data is to be in a non-native
  127. byte order (within each chunk), then you will need to create an iterator
  128. adaptor that presents it in native order (see <a href="http://www.boost.org/doc/libs/release/libs/endian/doc/index.html" target="_top">Boost.Endian</a>).
  129. </p>
  130. <div class="note"><table border="0" summary="Note">
  131. <tr>
  132. <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
  133. <th align="left">Note</th>
  134. </tr>
  135. <tr><td align="left" valign="top"><p>
  136. Note that this function is optimized for the case where the data can be
  137. <code class="computeroutput"><span class="identifier">memcpy</span></code>ed from the source
  138. to the integer - in this case both iterators much be pointers, and everything
  139. must be little-endian.
  140. </p></td></tr>
  141. </table></div>
  142. <h5>
  143. <a name="boost_multiprecision.tut.import_export.h0"></a>
  144. <span class="phrase"><a name="boost_multiprecision.tut.import_export.examples"></a></span><a class="link" href="import_export.html#boost_multiprecision.tut.import_export.examples">Examples</a>
  145. </h5>
  146. <p>
  147. In this simple example, we'll import/export the bits of a cpp_int to a vector
  148. of 8-bit unsigned values:
  149. </p>
  150. <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">cpp_int</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  151. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
  152. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iomanip</span><span class="special">&gt;</span>
  153. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
  154. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iterator</span><span class="special">&gt;</span>
  155. <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
  156. <span class="special">{</span>
  157. <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">cpp_int</span><span class="special">;</span>
  158. <span class="comment">// Create a cpp_int with just a couple of bits set:</span>
  159. <span class="identifier">cpp_int</span> <span class="identifier">i</span><span class="special">;</span>
  160. <span class="identifier">bit_set</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="number">5000</span><span class="special">);</span> <span class="comment">// set the 5000'th bit</span>
  161. <span class="identifier">bit_set</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="number">200</span><span class="special">);</span>
  162. <span class="identifier">bit_set</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="number">50</span><span class="special">);</span>
  163. <span class="comment">// export into 8-bit unsigned values, most significant bit first:</span>
  164. <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">v</span><span class="special">;</span>
  165. <span class="identifier">export_bits</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">back_inserter</span><span class="special">(</span><span class="identifier">v</span><span class="special">),</span> <span class="number">8</span><span class="special">);</span>
  166. <span class="comment">// import back again, and check for equality:</span>
  167. <span class="identifier">cpp_int</span> <span class="identifier">j</span><span class="special">;</span>
  168. <span class="identifier">import_bits</span><span class="special">(</span><span class="identifier">j</span><span class="special">,</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span>
  169. <span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="identifier">j</span><span class="special">);</span>
  170. <span class="special">}</span>
  171. </pre>
  172. <p>
  173. Importing or exporting cpp_bin_float is similar, but we must procede via
  174. an intermediate integer:
  175. </p>
  176. <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">multiprecision</span><span class="special">/</span><span class="identifier">cpp_bin_float</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  177. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
  178. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iomanip</span><span class="special">&gt;</span>
  179. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">vector</span><span class="special">&gt;</span>
  180. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iterator</span><span class="special">&gt;</span>
  181. <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
  182. <span class="special">{</span>
  183. <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">cpp_bin_float_100</span><span class="special">;</span>
  184. <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">multiprecision</span><span class="special">::</span><span class="identifier">cpp_int</span><span class="special">;</span>
  185. <span class="comment">// Create a cpp_bin_float to import/export:</span>
  186. <span class="identifier">cpp_bin_float_100</span> <span class="identifier">f</span><span class="special">(</span><span class="number">1</span><span class="special">);</span>
  187. <span class="identifier">f</span> <span class="special">/=</span> <span class="number">3</span><span class="special">;</span>
  188. <span class="comment">// export into 8-bit unsigned values, most significant bit first:</span>
  189. <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">&gt;</span> <span class="identifier">v</span><span class="special">;</span>
  190. <span class="identifier">export_bits</span><span class="special">(</span><span class="identifier">cpp_int</span><span class="special">(</span><span class="identifier">f</span><span class="special">.</span><span class="identifier">backend</span><span class="special">().</span><span class="identifier">bits</span><span class="special">()),</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">back_inserter</span><span class="special">(</span><span class="identifier">v</span><span class="special">),</span> <span class="number">8</span><span class="special">);</span>
  191. <span class="comment">// Grab the exponent as well:</span>
  192. <span class="keyword">int</span> <span class="identifier">e</span> <span class="special">=</span> <span class="identifier">f</span><span class="special">.</span><span class="identifier">backend</span><span class="special">().</span><span class="identifier">exponent</span><span class="special">();</span>
  193. <span class="comment">// Import back again, and check for equality, we have to procede via</span>
  194. <span class="comment">// an intermediate integer:</span>
  195. <span class="identifier">cpp_int</span> <span class="identifier">i</span><span class="special">;</span>
  196. <span class="identifier">import_bits</span><span class="special">(</span><span class="identifier">i</span><span class="special">,</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span>
  197. <span class="identifier">cpp_bin_float_100</span> <span class="identifier">g</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
  198. <span class="identifier">g</span><span class="special">.</span><span class="identifier">backend</span><span class="special">().</span><span class="identifier">exponent</span><span class="special">()</span> <span class="special">=</span> <span class="identifier">e</span><span class="special">;</span>
  199. <span class="identifier">BOOST_ASSERT</span><span class="special">(</span><span class="identifier">f</span> <span class="special">==</span> <span class="identifier">g</span><span class="special">);</span>
  200. <span class="special">}</span>
  201. </pre>
  202. </div>
  203. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
  204. <td align="left"></td>
  205. <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2019 John Maddock
  206. and Christopher Kormanyos<p>
  207. Distributed under the Boost Software License, Version 1.0. (See accompanying
  208. 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>)
  209. </p>
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