Function IPERM

src/cryptopp/des.cpp:76–96

Wei Dai's modification to Richard Outerbridge's initial permutation algorithm, this one is faster if you have access to rotate instructions (like in MSVC)

// algorithm, this one is faster if you have access to rotate instructions
// (like in MSVC)
static inline void IPERM(word32 &left, word32 &right)
{
	word32 work;

	right = rotlFixed(right, 4U);
	work = (left ^ right) & 0xf0f0f0f0;
	left ^= work;
	right = rotrFixed(right^work, 20U);
	work = (left ^ right) & 0xffff0000;
	left ^= work;
	right = rotrFixed(right^work, 18U);
	work = (left ^ right) & 0x33333333;
	left ^= work;
	right = rotrFixed(right^work, 6U);
	work = (left ^ right) & 0x00ff00ff;
	left ^= work;
	right = rotlFixed(right^work, 9U);
	work = (left ^ right) & 0xaaaaaaaa;
	left = rotlFixed(left^work, 1U);
	right ^= work;
}

static inline void FPERM(word32 &left, word32 &right)
{