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<div class="title">gf256.cpp</div> </div>
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<div class="fragment"><pre class="fragment"><a name="l00001"></a>00001 <span class="comment">// gf256.cpp - written and placed in the public domain by Wei Dai</span>
<a name="l00002"></a>00002
<a name="l00003"></a>00003 <span class="preprocessor">#include "pch.h"</span>
<a name="l00004"></a>00004 <span class="preprocessor">#include "gf256.h"</span>
<a name="l00005"></a>00005
<a name="l00006"></a>00006 NAMESPACE_BEGIN(CryptoPP)
<a name="l00007"></a>00007
<a name="l00008"></a>00008 <a class="code" href="class_g_f256.html" title="GF(256) with polynomial basis.">GF256</a>::Element <a class="code" href="class_g_f256.html" title="GF(256) with polynomial basis.">GF256</a>::Multiply(Element a, Element b)<span class="keyword"> const</span>
<a name="l00009"></a>00009 <span class="keyword"></span>{
<a name="l00010"></a>00010 word result = 0, t = b;
<a name="l00011"></a>00011
<a name="l00012"></a>00012 <span class="keywordflow">for</span> (<span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> i=0; i<8; i++)
<a name="l00013"></a>00013 {
<a name="l00014"></a>00014 result <<= 1;
<a name="l00015"></a>00015 <span class="keywordflow">if</span> (result & 0x100)
<a name="l00016"></a>00016 result ^= m_modulus;
<a name="l00017"></a>00017
<a name="l00018"></a>00018 t <<= 1;
<a name="l00019"></a>00019 <span class="keywordflow">if</span> (t & 0x100)
<a name="l00020"></a>00020 result ^= a;
<a name="l00021"></a>00021 }
<a name="l00022"></a>00022
<a name="l00023"></a>00023 <span class="keywordflow">return</span> (GF256::Element) result;
<a name="l00024"></a>00024 }
<a name="l00025"></a>00025
<a name="l00026"></a>00026 GF256::Element GF256::MultiplicativeInverse(Element a)<span class="keyword"> const</span>
<a name="l00027"></a>00027 <span class="keyword"></span>{
<a name="l00028"></a>00028 Element result = a;
<a name="l00029"></a>00029 <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i=1; i<7; i++)
<a name="l00030"></a>00030 result = Multiply(<a class="code" href="class_square.html" title="Square">Square</a>(result), a);
<a name="l00031"></a>00031 <span class="keywordflow">return</span> <a class="code" href="class_square.html" title="Square">Square</a>(result);
<a name="l00032"></a>00032 }
<a name="l00033"></a>00033
<a name="l00034"></a>00034 NAMESPACE_END
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