gf2_32.cpp

各种加密算法的集合

#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); 
	} 
 
#ifdef FAST_ROTATE 
	b = rotr(b, 30U); 
	word32 result = table[b&2]; 
 
	for (int i=29; i>=0; --i) 
	{ 
		b = rotl(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