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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html;charset=UTF-8"><title>Crypto++: gf2_32.cpp Source File</title><link href="doxygen.css" rel="stylesheet" type="text/css"><link href="tabs.css" rel="stylesheet" type="text/css"></head><body><!-- Generated by Doxygen 1.5.2 --><div class="tabs"> <ul> <li><a href="index.html"><span>Main Page</span></a></li> <li><a href="namespaces.html"><span>Namespaces</span></a></li> <li><a href="classes.html"><span>Classes</span></a></li> <li class="current"><a href="files.html"><span>Files</span></a></li> </ul></div><div class="tabs"> <ul> <li><a href="files.html"><span>File List</span></a></li> <li><a href="globals.html"><span>File Members</span></a></li> </ul></div><h1>gf2_32.cpp</h1><div class="fragment"><pre class="fragment"><a name="l00001"></a>00001 <span class="comment">// gf2_32.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 "misc.h"</span><a name="l00005"></a>00005 <span class="preprocessor">#include "gf2_32.h"</span><a name="l00006"></a>00006 <a name="l00007"></a>00007 NAMESPACE_BEGIN(CryptoPP)<a name="l00008"></a>00008 <a name="l00009"></a><a class="code" href="class_g_f2__32.html#6742fc1b3c53d966cf6ec77b8ec12102">00009</a> <a class="code" href="class_g_f2__32.html" title="GF(2^32) with polynomial basis.">GF2_32</a>::Element <a class="code" href="class_g_f2__32.html" title="GF(2^32) with polynomial basis.">GF2_32</a>::Multiply(Element a, Element b)<span class="keyword"> const</span><a name="l00010"></a>00010 <span class="keyword"></span>{<a name="l00011"></a>00011 word32 table[4];<a name="l00012"></a>00012 table[0] = 0;<a name="l00013"></a>00013 table[1] = m_modulus;<a name="l00014"></a>00014 <span class="keywordflow">if</span> (a & 0x80000000)<a name="l00015"></a>00015 {<a name="l00016"></a>00016 table[2] = m_modulus ^ (a<<1);<a name="l00017"></a>00017 table[3] = a<<1;<a name="l00018"></a>00018 }<a name="l00019"></a>00019 <span class="keywordflow">else</span><a name="l00020"></a>00020 {<a name="l00021"></a>00021 table[2] = a<<1;<a name="l00022"></a>00022 table[3] = m_modulus ^ (a<<1);<a name="l00023"></a>00023 }<a name="l00024"></a>00024 <a name="l00025"></a>00025 <span class="preprocessor">#if CRYPTOPP_FAST_ROTATE(32)</span><a name="l00026"></a>00026 <span class="preprocessor"></span> b = rotrFixed(b, 30U);<a name="l00027"></a>00027 word32 result = table[b&2];<a name="l00028"></a>00028 <a name="l00029"></a>00029 <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i=29; i>=0; --i)<a name="l00030"></a>00030 {<a name="l00031"></a>00031 b = rotlFixed(b, 1U);<a name="l00032"></a>00032 result = (result<<1) ^ table[(b&2) + (result>>31)];<a name="l00033"></a>00033 }<a name="l00034"></a>00034 <a name="l00035"></a>00035 <span class="keywordflow">return</span> (b&1) ? result ^ a : result;<a name="l00036"></a>00036 <span class="preprocessor">#else</span><a name="l00037"></a>00037 <span class="preprocessor"></span> word32 result = table[(b>>30) & 2];<a name="l00038"></a>00038 <a name="l00039"></a>00039 <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i=29; i>=0; --i)<a name="l00040"></a>00040 result = (result<<1) ^ table[((b>>i)&2) + (result>>31)];<a name="l00041"></a>00041 <a name="l00042"></a>00042 <span class="keywordflow">return</span> (b&1) ? result ^ a : result;<a name="l00043"></a>00043 <span class="preprocessor">#endif</span><a name="l00044"></a>00044 <span class="preprocessor"></span>}<a name="l00045"></a>00045 <a name="l00046"></a><a class="code" href="class_g_f2__32.html#fbab6b99b72ab336fc99aa2d91540277">00046</a> <a class="code" href="class_g_f2__32.html#72d3258fb8c36f2bb8a544b96d453a03">GF2_32::Element</a> <a class="code" href="class_g_f2__32.html#fbab6b99b72ab336fc99aa2d91540277">GF2_32::MultiplicativeInverse</a>(Element a)<span class="keyword"> const</span><a name="l00047"></a>00047 <span class="keyword"></span>{<a name="l00048"></a>00048 <span class="keywordflow">if</span> (a <= 1) <span class="comment">// 1 is a special case</span><a name="l00049"></a>00049 <span class="keywordflow">return</span> a;<a name="l00050"></a>00050 <a name="l00051"></a>00051 <span class="comment">// warning - don't try to adapt this algorithm for another situation</span><a name="l00052"></a>00052 word32 g0=m_modulus, g1=a, g2=a;<a name="l00053"></a>00053 word32 v0=0, v1=1, v2=1;<a name="l00054"></a>00054 <a name="l00055"></a>00055 assert(g1);<a name="l00056"></a>00056 <a name="l00057"></a>00057 <span class="keywordflow">while</span> (!(g2 & 0x80000000))<a name="l00058"></a>00058 {<a name="l00059"></a>00059 g2 <<= 1;<a name="l00060"></a>00060 v2 <<= 1;<a name="l00061"></a>00061 }<a name="l00062"></a>00062 <a name="l00063"></a>00063 g2 <<= 1;<a name="l00064"></a>00064 v2 <<= 1;<a name="l00065"></a>00065 <a name="l00066"></a>00066 g0 ^= g2;<a name="l00067"></a>00067 v0 ^= v2;<a name="l00068"></a>00068 <a name="l00069"></a>00069 <span class="keywordflow">while</span> (g0 != 1)<a name="l00070"></a>00070 {<a name="l00071"></a>00071 <span class="keywordflow">if</span> (g1 < g0 || ((g0^g1) < g0 && (g0^g1) < g1))<a name="l00072"></a>00072 {<a name="l00073"></a>00073 assert(BitPrecision(g1) <= BitPrecision(g0));<a name="l00074"></a>00074 g2 = g1;<a name="l00075"></a>00075 v2 = v1;<a name="l00076"></a>00076 }<a name="l00077"></a>00077 <span class="keywordflow">else</span><a name="l00078"></a>00078 {<a name="l00079"></a>00079 assert(BitPrecision(g1) > BitPrecision(g0));<a name="l00080"></a>00080 g2 = g0; g0 = g1; g1 = g2;<a name="l00081"></a>00081 v2 = v0; v0 = v1; v1 = v2;<a name="l00082"></a>00082 }<a name="l00083"></a>00083 <a name="l00084"></a>00084 <span class="keywordflow">while</span> ((g0^g2) >= g2)<a name="l00085"></a>00085 {<a name="l00086"></a>00086 assert(BitPrecision(g0) > BitPrecision(g2));<a name="l00087"></a>00087 g2 <<= 1;<a name="l00088"></a>00088 v2 <<= 1;<a name="l00089"></a>00089 }<a name="l00090"></a>00090 <a name="l00091"></a>00091 assert(BitPrecision(g0) == BitPrecision(g2));<a name="l00092"></a>00092 g0 ^= g2;<a name="l00093"></a>00093 v0 ^= v2;<a name="l00094"></a>00094 }<a name="l00095"></a>00095 <a name="l00096"></a>00096 <span class="keywordflow">return</span> v0;<a name="l00097"></a>00097 }<a name="l00098"></a>00098 <a name="l00099"></a>00099 NAMESPACE_END</pre></div><hr size="1"><address style="text-align: right;"><small>Generated on Fri Jun 1 11:11:21 2007 for Crypto++ by <a href="http://www.doxygen.org/index.html"><img src="doxygen.png" alt="doxygen" align="middle" border="0"></a> 1.5.2 </small></address></body></html>⌨️ 快捷键说明
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