MD5 review

#include "md5p.h"

typedef unsigned long (*_md5_nl)(unsigned long,unsigned long,unsigned long);

static const unsigned long _md5_a = 0x67452301UL;
static const unsigned long _md5_b = 0xefcdab89UL;
static const unsigned long _md5_c = 0x98badcfeUL;
static const unsigned long _md5_d = 0x10325476UL;

static int _md5_n[4][2] = {
	{0, 1},
	{1, 5},
	{5, 3},
	{0, 7}
};

static unsigned long _md5_s[4][4] = {
	{ 7, 12, 17, 22},
	{ 5,  9, 14, 20},
	{ 4, 11, 16, 23},
	{ 6, 10, 15, 21}
};

static unsigned long _md5_t[4][16] = {
	{0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee, 0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
	 0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be, 0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821},
	{0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa, 0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
	 0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed, 0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a},
	{0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c, 0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
	 0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05, 0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665},
	{0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039, 0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
	 0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1, 0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391}
};

static inline unsigned long _md5_rol(unsigned long n, unsigned long c)
{
	return (n << c) | (n >> (32 - c));
}

static inline void _md5_xx(unsigned long& a, unsigned long b, unsigned long r, unsigned long M, unsigned long s, unsigned long t)
{
	a = b + _md5_rol(a + r + M + t, s);
}

static inline unsigned long _md5_f(unsigned long x, unsigned long y, unsigned long z)
{
	return (x & y) | ((~x) & z);
}

static inline unsigned long _md5_g(unsigned long x, unsigned long y, unsigned long z)
{
	return (x & z) | (y & (~z));
}

static inline unsigned long _md5_h(unsigned long x, unsigned long y, unsigned long z)
{
	return (x ^ y ^ z);
}

static inline unsigned long _md5_i(unsigned long x, unsigned long y, unsigned long z)
{
	return y ^ (x | (~z));
}

void MD5p::Initialize(unsigned long chain[4])
{
	chain[0] = _md5_a;
	chain[1] = _md5_b;
	chain[2] = _md5_c;
	chain[3] = _md5_d;
	return;
}

void MD5p::Update(unsigned long chain[4], unsigned long M[16])
{
	_md5_nl FN[4] = {
		_md5_f,
		_md5_g,
		_md5_h,
		_md5_i
	};
	unsigned long state[4];
	for (int i = 0; i < 4; i++) {
		state[i] = chain[i];
	}
	for (int i = 0; i < 4; i++) {
		int n = _md5_n[i][0];
		for (int j = 0; j < 16; j++) {
			int k = ((4 - (j & 3)) & 3);
			_md5_xx(state[k], state[(k + 1) & 3], FN[i](state[(k + 1) & 3], state[(k + 2) & 3], state[(k + 3) & 3]), M[n & 0xf], _md5_s[i][j & 3], _md5_t[i][j]);
			n += _md5_n[i][1];
		}
	}
	for (int i = 0; i < 4; i++) {
		chain[i] += state[i];
	}
}

void MD5p::Final(unsigned long chain[4], unsigned char* tail, unsigned long length[2])
{
	unsigned char E[128];

	int l = length[0] & 0x3f;
	int p = 0;
	for (p = 0; p < l; p++) {
		E[p] = tail[p];
	}
	int n = (l >= 56? 120: 56) - l;
	if (n > 0) {
		E[p++] = 0x80;
		while (--n > 0) {
			E[p++] = 0;
		}
	}
	((unsigned long *)(E + p))[0] = length[0] << 3;
	((unsigned long *)(E + p))[1] = length[1] << 3 | length[0] >> 29;
	Update(chain, (unsigned long *)E);
	if(l >= 56) {
		Update(chain, (unsigned long *)&E[64]);
	}
}