mirror of
https://github.com/shadps4-emu/ext-cryptopp.git
synced 2024-11-23 18:09:48 +00:00
100 lines
1.8 KiB
C++
100 lines
1.8 KiB
C++
// gf2_32.cpp - originally 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 = rotrConstant<30>(b);
|
|
word32 result = table[b&2];
|
|
|
|
for (int i=29; i>=0; --i)
|
|
{
|
|
b = rotlConstant<1>(b);
|
|
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;
|
|
|
|
CRYPTOPP_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))
|
|
{
|
|
CRYPTOPP_ASSERT(BitPrecision(g1) <= BitPrecision(g0));
|
|
g2 = g1;
|
|
v2 = v1;
|
|
}
|
|
else
|
|
{
|
|
CRYPTOPP_ASSERT(BitPrecision(g1) > BitPrecision(g0));
|
|
g2 = g0; g0 = g1; g1 = g2;
|
|
v2 = v0; v0 = v1; v1 = v2;
|
|
}
|
|
|
|
while ((g0^g2) >= g2)
|
|
{
|
|
CRYPTOPP_ASSERT(BitPrecision(g0) > BitPrecision(g2));
|
|
g2 <<= 1;
|
|
v2 <<= 1;
|
|
}
|
|
|
|
CRYPTOPP_ASSERT(BitPrecision(g0) == BitPrecision(g2));
|
|
g0 ^= g2;
|
|
v0 ^= v2;
|
|
}
|
|
|
|
return v0;
|
|
}
|
|
|
|
NAMESPACE_END
|