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authorAlexander Harkness <bearbin@gmail.com>2013-11-24 15:21:13 +0100
committerAlexander Harkness <bearbin@gmail.com>2013-11-24 15:21:13 +0100
commit3438e5d3ddf8444f0e31009ffbe8237ef3752c22 (patch)
tree7c2f76d5e9281c130e60fb932c4dda89a49863b6 /lib/cryptopp/gf2_32.cpp
parentMoved source to src (diff)
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Diffstat (limited to 'lib/cryptopp/gf2_32.cpp')
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1 files changed, 99 insertions, 0 deletions
diff --git a/lib/cryptopp/gf2_32.cpp b/lib/cryptopp/gf2_32.cpp
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+++ b/lib/cryptopp/gf2_32.cpp
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+// gf2_32.cpp - written and placed in the public domain by Wei Dai
+
+#include "pch.h"
+#include "misc.h"
+#include "gf2_32.h"
+
+NAMESPACE_BEGIN(CryptoPP)
+
+GF2_32::Element GF2_32::Multiply(Element a, Element b) const
+{
+ word32 table[4];
+ table[0] = 0;
+ table[1] = m_modulus;
+ if (a & 0x80000000)
+ {
+ table[2] = m_modulus ^ (a<<1);
+ table[3] = a<<1;
+ }
+ else
+ {
+ table[2] = a<<1;
+ table[3] = m_modulus ^ (a<<1);
+ }
+
+#if CRYPTOPP_FAST_ROTATE(32)
+ b = rotrFixed(b, 30U);
+ word32 result = table[b&2];
+
+ for (int i=29; i>=0; --i)
+ {
+ b = rotlFixed(b, 1U);
+ result = (result<<1) ^ table[(b&2) + (result>>31)];
+ }
+
+ return (b&1) ? result ^ a : result;
+#else
+ word32 result = table[(b>>30) & 2];
+
+ for (int i=29; i>=0; --i)
+ result = (result<<1) ^ table[((b>>i)&2) + (result>>31)];
+
+ return (b&1) ? result ^ a : result;
+#endif
+}
+
+GF2_32::Element GF2_32::MultiplicativeInverse(Element a) const
+{
+ if (a <= 1) // 1 is a special case
+ return a;
+
+ // warning - don't try to adapt this algorithm for another situation
+ word32 g0=m_modulus, g1=a, g2=a;
+ word32 v0=0, v1=1, v2=1;
+
+ assert(g1);
+
+ while (!(g2 & 0x80000000))
+ {
+ g2 <<= 1;
+ v2 <<= 1;
+ }
+
+ g2 <<= 1;
+ v2 <<= 1;
+
+ g0 ^= g2;
+ v0 ^= v2;
+
+ while (g0 != 1)
+ {
+ if (g1 < g0 || ((g0^g1) < g0 && (g0^g1) < g1))
+ {
+ assert(BitPrecision(g1) <= BitPrecision(g0));
+ g2 = g1;
+ v2 = v1;
+ }
+ else
+ {
+ assert(BitPrecision(g1) > BitPrecision(g0));
+ g2 = g0; g0 = g1; g1 = g2;
+ v2 = v0; v0 = v1; v1 = v2;
+ }
+
+ while ((g0^g2) >= g2)
+ {
+ assert(BitPrecision(g0) > BitPrecision(g2));
+ g2 <<= 1;
+ v2 <<= 1;
+ }
+
+ assert(BitPrecision(g0) == BitPrecision(g2));
+ g0 ^= g2;
+ v0 ^= v2;
+ }
+
+ return v0;
+}
+
+NAMESPACE_END