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<div class="section" id="module-crcmod.predefined">
<h1><tt class="xref docutils literal"><span class="pre">crcmod.predefined</span></tt> – CRC calculation using predefined algorithms<a class="headerlink" href="#module-crcmod.predefined" title="Permalink to this headline">¶</a></h1>
<p>This module provides a function factory <a title="crcmod.predefined.mkPredefinedCrcFun" class="reference internal" href="#crcmod.predefined.mkPredefinedCrcFun"><tt class="xref docutils literal"><span class="pre">mkPredefinedCrcFun()</span></tt></a> and a class <a title="crcmod.predefined.PredefinedCrc" class="reference internal" href="#crcmod.predefined.PredefinedCrc"><tt class="xref docutils literal"><span class="pre">PredefinedCrc</span></tt></a>
for calculating CRCs of byte strings using common predefined CRC algorithms.</p>
<p>The function factory and the class are very similar to those defined in <a title="CRC calculation" class="reference external" href="crcmod.html#module-crcmod"><tt class="xref docutils literal"><span class="pre">crcmod</span></tt></a>,
except that the CRC algorithm is specified by a predefined name, rather than the
individual polynomial, reflection, and initial and final-XOR parameters.</p>
<div class="section" id="predefined-crc-algorithms">
<h2>Predefined CRC algorithms<a class="headerlink" href="#predefined-crc-algorithms" title="Permalink to this headline">¶</a></h2>
<p>The <tt class="xref docutils literal"><span class="pre">crcmod.predefined</span></tt> module offers the following predefined algorithms:</p>
<table border="1" class="docutils">
<colgroup>
<col width="26%" />
<col width="18%" />
<col width="8%" />
<col width="16%" />
<col width="16%" />
<col width="16%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Name</th>
<th class="head">Polynomial</th>
<th class="head">Reversed?</th>
<th class="head">Init-value</th>
<th class="head">XOR-out</th>
<th class="head">Check</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">crc-8</span></tt></td>
<td>0x107</td>
<td>False</td>
<td>0x00</td>
<td>0x00</td>
<td>0xF4</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-8-darc</span></tt></td>
<td>0x139</td>
<td>True</td>
<td>0x00</td>
<td>0x00</td>
<td>0x15</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-8-i-code</span></tt></td>
<td>0x11D</td>
<td>False</td>
<td>0xFD</td>
<td>0x00</td>
<td>0x7E</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-8-itu</span></tt></td>
<td>0x107</td>
<td>False</td>
<td>0x55</td>
<td>0x55</td>
<td>0xA1</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-8-maxim</span></tt></td>
<td>0x131</td>
<td>True</td>
<td>0x00</td>
<td>0x00</td>
<td>0xA1</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-8-rohc</span></tt></td>
<td>0x107</td>
<td>True</td>
<td>0xFF</td>
<td>0x00</td>
<td>0xD0</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-8-wcdma</span></tt></td>
<td>0x19B</td>
<td>True</td>
<td>0x00</td>
<td>0x00</td>
<td>0x25</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16</span></tt></td>
<td>0x18005</td>
<td>True</td>
<td>0x0000</td>
<td>0x0000</td>
<td>0xBB3D</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-buypass</span></tt></td>
<td>0x18005</td>
<td>False</td>
<td>0x0000</td>
<td>0x0000</td>
<td>0xFEE8</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-dds-110</span></tt></td>
<td>0x18005</td>
<td>False</td>
<td>0x800D</td>
<td>0x0000</td>
<td>0x9ECF</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-dect</span></tt></td>
<td>0x10589</td>
<td>False</td>
<td>0x0001</td>
<td>0x0001</td>
<td>0x007E</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-dnp</span></tt></td>
<td>0x13D65</td>
<td>True</td>
<td>0xFFFF</td>
<td>0xFFFF</td>
<td>0xEA82</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-en-13757</span></tt></td>
<td>0x13D65</td>
<td>False</td>
<td>0xFFFF</td>
<td>0xFFFF</td>
<td>0xC2B7</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-genibus</span></tt></td>
<td>0x11021</td>
<td>False</td>
<td>0x0000</td>
<td>0xFFFF</td>
<td>0xD64E</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-maxim</span></tt></td>
<td>0x18005</td>
<td>True</td>
<td>0xFFFF</td>
<td>0xFFFF</td>
<td>0x44C2</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-mcrf4xx</span></tt></td>
<td>0x11021</td>
<td>True</td>
<td>0xFFFF</td>
<td>0x0000</td>
<td>0x6F91</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-riello</span></tt></td>
<td>0x11021</td>
<td>True</td>
<td>0x554D</td>
<td>0x0000</td>
<td>0x63D0</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-t10-dif</span></tt></td>
<td>0x18BB7</td>
<td>False</td>
<td>0x0000</td>
<td>0x0000</td>
<td>0xD0DB</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-teledisk</span></tt></td>
<td>0x1A097</td>
<td>False</td>
<td>0x0000</td>
<td>0x0000</td>
<td>0x0FB3</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-16-usb</span></tt></td>
<td>0x18005</td>
<td>True</td>
<td>0x0000</td>
<td>0xFFFF</td>
<td>0xB4C8</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">x-25</span></tt></td>
<td>0x11021</td>
<td>True</td>
<td>0x0000</td>
<td>0xFFFF</td>
<td>0x906E</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">xmodem</span></tt></td>
<td>0x11021</td>
<td>False</td>
<td>0x0000</td>
<td>0x0000</td>
<td>0x31C3</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">modbus</span></tt></td>
<td>0x18005</td>
<td>True</td>
<td>0xFFFF</td>
<td>0x0000</td>
<td>0x4B37</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">kermit</span></tt> <a class="footnote-reference" href="#ccitt" id="id1">[1]</a></td>
<td>0x11021</td>
<td>True</td>
<td>0x0000</td>
<td>0x0000</td>
<td>0x2189</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-ccitt-false</span></tt> <a class="footnote-reference" href="#ccitt" id="id2">[1]</a></td>
<td>0x11021</td>
<td>False</td>
<td>0xFFFF</td>
<td>0x0000</td>
<td>0x29B1</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-aug-ccitt</span></tt> <a class="footnote-reference" href="#ccitt" id="id3">[1]</a></td>
<td>0x11021</td>
<td>False</td>
<td>0x1D0F</td>
<td>0x0000</td>
<td>0xE5CC</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-24</span></tt></td>
<td>0x1864CFB</td>
<td>False</td>
<td>0xB704CE</td>
<td>0x000000</td>
<td>0x21CF02</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-24-flexray-a</span></tt></td>
<td>0x15D6DCB</td>
<td>False</td>
<td>0xFEDCBA</td>
<td>0x000000</td>
<td>0x7979BD</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-24-flexray-b</span></tt></td>
<td>0x15D6DCB</td>
<td>False</td>
<td>0xABCDEF</td>
<td>0x000000</td>
<td>0x1F23B8</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-32</span></tt></td>
<td>0x104C11DB7</td>
<td>True</td>
<td>0x00000000</td>
<td>0xFFFFFFFF</td>
<td>0xCBF43926</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-32-bzip2</span></tt></td>
<td>0x104C11DB7</td>
<td>False</td>
<td>0x00000000</td>
<td>0xFFFFFFFF</td>
<td>0xFC891918</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-32c</span></tt></td>
<td>0x11EDC6F41</td>
<td>True</td>
<td>0x00000000</td>
<td>0xFFFFFFFF</td>
<td>0xE3069283</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-32d</span></tt></td>
<td>0x1A833982B</td>
<td>True</td>
<td>0x00000000</td>
<td>0xFFFFFFFF</td>
<td>0x87315576</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-32-mpeg</span></tt></td>
<td>0x104C11DB7</td>
<td>False</td>
<td>0xFFFFFFFF</td>
<td>0x00000000</td>
<td>0x0376E6E7</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">posix</span></tt></td>
<td>0x104C11DB7</td>
<td>False</td>
<td>0xFFFFFFFF</td>
<td>0xFFFFFFFF</td>
<td>0x765E7680</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-32q</span></tt></td>
<td>0x1814141AB</td>
<td>False</td>
<td>0x00000000</td>
<td>0x00000000</td>
<td>0x3010BF7F</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">jamcrc</span></tt></td>
<td>0x104C11DB7</td>
<td>True</td>
<td>0xFFFFFFFF</td>
<td>0x00000000</td>
<td>0x340BC6D9</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">xfer</span></tt></td>
<td>0x1000000AF</td>
<td>False</td>
<td>0x00000000</td>
<td>0x00000000</td>
<td>0xBD0BE338</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-64</span></tt></td>
<td>0x1000000000000001B</td>
<td>True</td>
<td>0x0000000000000000</td>
<td>0x0000000000000000</td>
<td>0x46A5A9388A5BEFFE</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-64-we</span></tt></td>
<td>0x142F0E1EBA9EA3693</td>
<td>False</td>
<td>0x0000000000000000</td>
<td>0xFFFFFFFFFFFFFFFF</td>
<td>0x62EC59E3F1A4F00A</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">crc-64-jones</span></tt></td>
<td>0x1AD93D23594C935A9</td>
<td>True</td>
<td>0xFFFFFFFFFFFFFFFF</td>
<td>0x0000000000000000</td>
<td>0xCAA717168609F281</td>
</tr>
</tbody>
</table>
<p class="rubric">Notes</p>
<table class="docutils footnote" frame="void" id="ccitt" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label">[1]</td><td><em>(<a class="fn-backref" href="#id1">1</a>, <a class="fn-backref" href="#id2">2</a>, <a class="fn-backref" href="#id3">3</a>)</em> <p>Definitions of CCITT are disputable. See:</p>
<ul class="last simple">
<li><a class="reference external" href="http://homepages.tesco.net/~rainstorm/crc-catalogue.htm">http://homepages.tesco.net/~rainstorm/crc-catalogue.htm</a></li>
<li><a class="reference external" href="http://web.archive.org/web/20071229021252/http://www.joegeluso.com/software/articles/ccitt.htm">http://web.archive.org/web/20071229021252/http://www.joegeluso.com/software/articles/ccitt.htm</a></li>
</ul>
</td></tr>
</tbody>
</table>
</div>
<div class="section" id="mkpredefinedcrcfun-crc-function-factory">
<h2><a title="crcmod.predefined.mkPredefinedCrcFun" class="reference internal" href="#crcmod.predefined.mkPredefinedCrcFun"><tt class="xref docutils literal"><span class="pre">mkPredefinedCrcFun()</span></tt></a> – CRC function factory<a class="headerlink" href="#mkpredefinedcrcfun-crc-function-factory" title="Permalink to this headline">¶</a></h2>
<p>The function factory provides a simple interface for CRC calculation. It is similar
to <a title="crcmod.mkCrcFun" class="reference external" href="crcmod.html#crcmod.mkCrcFun"><tt class="xref docutils literal"><span class="pre">crcmod.mkCrcFun()</span></tt></a>, except that it specifies a CRC algorithm by name rather
than its parameters.</p>
<dl class="function">
<dt id="crcmod.predefined.mkPredefinedCrcFun">
<tt class="descclassname">crcmod.predefined.</tt><tt class="descname">mkPredefinedCrcFun</tt><big>(</big><em>crc_name</em><big>)</big><a class="headerlink" href="#crcmod.predefined.mkPredefinedCrcFun" title="Permalink to this definition">¶</a></dt>
<dd><p>Function factory that returns a new function for calculating CRCs
using a specified CRC algorithm.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Parameter:</th><td class="field-body"><em>crc_name</em> (string) – The name of the predefined CRC algorithm to use.</td>
</tr>
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">CRC calculation function</td>
</tr>
<tr class="field"><th class="field-name">Return type:</th><td class="field-body">function</td>
</tr>
</tbody>
</table>
<p>The function that is returned is the same as that returned by <a title="crcmod.mkCrcFun" class="reference external" href="crcmod.html#crcmod.mkCrcFun"><tt class="xref docutils literal"><span class="pre">crcmod.mkCrcFun()</span></tt></a>:</p>
<dl class="function">
<dt id="crcmod.predefined..crc_function">
<tt class="descclassname">.</tt><tt class="descname">crc_function</tt><big>(</big><em>data</em><span class="optional">[</span>, <em>crc=initCrc</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#crcmod.predefined..crc_function" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><em>data</em> (byte string) – Data for which to calculate the CRC.</li>
<li><em>crc</em> – Initial CRC value.</li>
</ul>
</td>
</tr>
<tr class="field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">Calculated CRC value.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">integer</p>
</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="function">
<dt id="crcmod.predefined.mkCrcFun">
<tt class="descclassname">crcmod.predefined.</tt><tt class="descname">mkCrcFun</tt><big>(</big><em>crc_name</em><big>)</big><a class="headerlink" href="#crcmod.predefined.mkCrcFun" title="Permalink to this definition">¶</a></dt>
<dd><p>This is an alias for <a title="crcmod.predefined.mkPredefinedCrcFun" class="reference internal" href="#crcmod.predefined.mkPredefinedCrcFun"><tt class="xref docutils literal"><span class="pre">crcmod.predefined.mkPredefinedCrcFun()</span></tt></a>. However, it is not defined when
<tt class="xref docutils literal"><span class="pre">crcmod.predefined</span></tt> is imported using the form:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">crcmod.predefined</span> <span class="kn">import</span> <span class="o">*</span>
</pre></div>
</div>
</dd></dl>
<div class="section" id="examples">
<h3>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h3>
<p><strong>CRC-32</strong> example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">crcmod.predefined</span>
<span class="gp">>>> </span><span class="n">crc32_func</span> <span class="o">=</span> <span class="n">crcmod</span><span class="o">.</span><span class="n">predefined</span><span class="o">.</span><span class="n">mkCrcFun</span><span class="p">(</span><span class="s">'crc-32'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">hex</span><span class="p">(</span><span class="n">crc32_func</span><span class="p">(</span><span class="s">'123456789'</span><span class="p">))</span>
<span class="go">'0xcbf43926L'</span>
</pre></div>
</div>
<p><strong>XMODEM</strong> example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">xmodem_crc_func</span> <span class="o">=</span> <span class="n">crcmod</span><span class="o">.</span><span class="n">predefined</span><span class="o">.</span><span class="n">mkCrcFun</span><span class="p">(</span><span class="s">'xmodem'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">hex</span><span class="p">(</span><span class="n">xmodem_crc_func</span><span class="p">(</span><span class="s">'123456789'</span><span class="p">))</span>
<span class="go">'0x31c3'</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="class-predefinedcrc">
<h2>Class <a title="crcmod.predefined.PredefinedCrc" class="reference internal" href="#crcmod.predefined.PredefinedCrc"><tt class="xref docutils literal"><span class="pre">PredefinedCrc</span></tt></a><a class="headerlink" href="#class-predefinedcrc" title="Permalink to this headline">¶</a></h2>
<p>This class is inherited from the <a title="crcmod.Crc" class="reference external" href="crcmod.html#crcmod.Crc"><tt class="xref docutils literal"><span class="pre">crcmod.Crc</span></tt></a> class, and is the same except for the
initialization. It specifies a CRC algorithm by name rather than its parameters.</p>
<dl class="class">
<dt id="crcmod.predefined.PredefinedCrc">
<em class="property">class </em><tt class="descclassname">crcmod.predefined.</tt><tt class="descname">PredefinedCrc</tt><big>(</big><em>crc_name</em><big>)</big><a class="headerlink" href="#crcmod.predefined.PredefinedCrc" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns a new <a title="crcmod.predefined.Crc" class="reference internal" href="#crcmod.predefined.Crc"><tt class="xref docutils literal"><span class="pre">Crc</span></tt></a> object for calculating CRCs using a specified CRC algorithm.</p>
<p>The parameter is the same as that for the factory function <a title="crcmod.predefined.mkPredefinedCrcFun" class="reference internal" href="#crcmod.predefined.mkPredefinedCrcFun"><tt class="xref docutils literal"><span class="pre">crcmod.predefined.mkPredefinedCrcFun()</span></tt></a>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Parameter:</th><td class="field-body"><em>crc_name</em> (string) – The name of the predefined CRC algorithm to use.</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="class">
<dt id="crcmod.predefined.Crc">
<em class="property">class </em><tt class="descclassname">crcmod.predefined.</tt><tt class="descname">Crc</tt><big>(</big><em>poly</em><span class="optional">[</span>, <em>initCrc</em>, <em>rev</em>, <em>xorOut</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#crcmod.predefined.Crc" title="Permalink to this definition">¶</a></dt>
<dd><p>This is an alias for <a title="crcmod.predefined.PredefinedCrc" class="reference internal" href="#crcmod.predefined.PredefinedCrc"><tt class="xref docutils literal"><span class="pre">crcmod.predefined.PredefinedCrc</span></tt></a>. However, it is not defined when
<tt class="xref docutils literal"><span class="pre">crcmod.predefined</span></tt> is imported using the form:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">crcmod.predefined</span> <span class="kn">import</span> <span class="o">*</span>
</pre></div>
</div>
</dd></dl>
<div class="section" id="id4">
<h3>Examples<a class="headerlink" href="#id4" title="Permalink to this headline">¶</a></h3>
<p><strong>CRC-32</strong> Example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">crcmod.predefined</span>
<span class="gp">>>> </span><span class="n">crc32</span> <span class="o">=</span> <span class="n">crcmod</span><span class="o">.</span><span class="n">predefined</span><span class="o">.</span><span class="n">Crc</span><span class="p">(</span><span class="s">'crc-32'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">crc32</span><span class="o">.</span><span class="n">update</span><span class="p">(</span><span class="s">'123456789'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">hex</span><span class="p">(</span><span class="n">crc32</span><span class="o">.</span><span class="n">crcValue</span><span class="p">)</span>
<span class="go">'0xcbf43926L'</span>
<span class="gp">>>> </span><span class="n">crc32</span><span class="o">.</span><span class="n">hexdigest</span><span class="p">()</span>
<span class="go">'CBF43926'</span>
</pre></div>
</div>
</div>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" href="#"><tt class="docutils literal"><span class="pre">crcmod.predefined</span></tt> – CRC calculation using predefined algorithms</a><ul>
<li><a class="reference external" href="#predefined-crc-algorithms">Predefined CRC algorithms</a></li>
<li><a class="reference external" href="#mkpredefinedcrcfun-crc-function-factory"><tt class="docutils literal"><span class="pre">mkPredefinedCrcFun()</span></tt> – CRC function factory</a><ul>
<li><a class="reference external" href="#examples">Examples</a></li>
</ul>
</li>
<li><a class="reference external" href="#class-predefinedcrc">Class <tt class="docutils literal"><span class="pre">PredefinedCrc</span></tt></a><ul>
<li><a class="reference external" href="#id4">Examples</a></li>
</ul>
</li>
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