md5.h

#pragma once

#define LEFTROTATE(x, c) (((x) << (c)) | ((x) >> (32 - (c))))
#include <fstream>

namespace md5 {
	inline void hash(const uint8_t* initial_msg, size_t initial_len, char* res) {

		uint32_t h0, h1, h2, h3;
		uint8_t* msg = NULL;

		static uint32_t r[] = {
			7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22,
			5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20,
			4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23,
			6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21
		};

		static uint32_t k[] = {
			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
		};

		h0 = 0x67452301;
		h1 = 0xefcdab89;
		h2 = 0x98badcfe;
		h3 = 0x10325476;

		size_t new_len = ((((initial_len + 8) / 64) + 1) * 64) - 8;

		msg = (uint8_t*)calloc(new_len + 64, 1);
		memcpy(msg, initial_msg, initial_len);
		msg[initial_len] = 128;
		size_t bits_len = 8 * initial_len;
		memcpy(msg + new_len, &bits_len, 4);

		for (int offset = 0; offset < new_len; offset += (512 / 8)) {
			uint32_t* w = (uint32_t*)(msg + offset);

			uint32_t a = h0;
			uint32_t b = h1;
			uint32_t c = h2;
			uint32_t d = h3;

			uint32_t i;
			for (i = 0; i < 64; i++) {
				uint32_t f, g;
				if (i < 16) {
					f = (b & c) | ((~b) & d);
					g = i;
				}
				else if (i < 32) {
					f = (d & b) | ((~d) & c);
					g = (5 * i + 1) % 16;
				}
				else if (i < 48) {
					f = b ^ c ^ d;
					g = (3 * i + 5) % 16;
				}
				else {
					f = c ^ (b | (~d));
					g = (7 * i) % 16;
				}
				uint32_t temp = d;
				d = c;
				c = b;
				b = b + LEFTROTATE((a + f + k[i] + w[g]), r[i]);
				a = temp;
			}

			h0 += a;
			h1 += b;
			h2 += c;
			h3 += d;
		}
		free(msg);
		uint8_t bytes[16];
		uint32_t* m5res = (uint32_t*)bytes;
		m5res[0] = h0;
		m5res[1] = h1;
		m5res[2] = h2;
		m5res[3] = h3;
		const char* chars16 = "0123456789abcdef";
		for (int i = 0, p = 0; i < 16; i++) {
			uint8_t b = bytes[i];
			res[p++] = chars16[b >> 4];
			res[p++] = chars16[b & 15];
		}
	}

	inline std::string hash(const uint8_t* initial_msg, size_t initial_len) {
		char c[33];
		hash(initial_msg, initial_len, c);
		c[32] = 0;
		return std::string(c);
	}
	
	inline std::string hash(const std::string& s) {
		return hash(reinterpret_cast<const uint8_t*>(s.c_str()), s.length());
	}

	inline std::string file_hash(const std::string& path) {
		size_t sz = std::filesystem::file_size(path);
		std::ifstream f(path, std::ios::binary);
		if (f.is_open()) {
			char* u = new char[sz];
			f.read(u, sz);
			f.close();
			return hash(reinterpret_cast<const uint8_t*>(u), sz);
		}
		return "";
	}
}