<?php
error_reporting(E_ALL | E_STRICT);

/**
 * Continued-hashing
 *
 * @author		Roland Haeder <roland@mxchange.org>
 * @copyright	Copyright (c) 2013 by Core Developer Team
 * @license		See LICENSE (public-domain)
 */

/**
 * Calculates a simple but stronger hash from given string. No salts are being
 * added here.
 *
 * @param	$str	The string to be hashed
 * @return	$hash	The hash from string $str
 */
function hashString ($str) {
	// Calculate strong hash from given string
	$hash = mhash(MHASH_RIPEMD320, $str);

	// Return it hexadecimal-encoded
	return bin2hex($hash);
}

/**
 * Double-hashes given string. This is done by hashing the given string and
 * then hashing the generated hash again.
 *
 * @param	$str	The string to be hashed 4 times
 * @return	$hash	The generated hash
 */
function doubleHashString ($str) {
	// Generate hash from given hash
	$hash = hashString(hashString($str));

	// Return it
	return $hash;
}

/**
 * Calculates a "modula-hash" based given two hashes.
 *
 * @param	$hash1	Hash 1
 * @param	$hash2	Hash 2
 */
function modulaHash ($hash1, $hash2) {
	// Both must have same length
	assert(strlen($hash1) === strlen($hash2));

	// Init new hash
	$modulaHash = '';

	// "Walk" trough first hash and get every 2 byte of both hashes
	for ($idx = 0; $idx < strlen($hash1); $idx += 2) {
		// Init modula value
		$mod = 0;

		// Get both hash parts and convert to ASCII number
		$part1 = hexdec(substr($hash1, $idx, 2));
		$part2 = hexdec(substr($hash2, $idx, 2));

		/*
		 * If part1 is larget part2, part1 is divident and vise-versa. But don't do it
		 * if one is zero
		 */
		if (($part1 > $part2) && ($part2 > 0)) {
			// 'part1' is larger than 'part2'
			$mod = $part1 % $part2;
		} elseif (($part1 < $part2) && ($part1 > 0)) {
			// 'part2' is larger than 'part1'
			$mod = $part2 % $part1;
		}

		// "Invert" the result against 255
		$mod = 255 - $mod;

		// Encode to hex, pre-pad it with zeros and add to new hash
		$modulaHash .= padHex($mod);
	} // END - for

	// Modula hash must have same length as input hash
	assert(strlen($modulaHash) === strlen($hash1));

	// Return modula hash
	return $modulaHash;
}

/**
 * Calculates a "sqrt-hash" based given two hashes and single-hash it
 *
 * @param	$hash1	Hash 1
 * @param	$hash2	Hash 2
 */
function sqrtHash ($hash1, $hash2) {
	// Both must have same length
	assert(strlen($hash1) === strlen($hash2));

	// Init new hash
	$sqrtHash = '';

	// "Walk" trough first hash and get every 2 byte of both hashes
	for ($idx = 0; $idx < strlen($hash1); $idx += 2) {
		// Init modula value
		$mod = 0;

		// Get both hash parts and convert to ASCII number
		$part1 = hexdec(substr($hash1, $idx, 2));
		$part2 = hexdec(substr($hash2, $idx, 2));

		// Calculate square root of both parts being multiplied and round up, then "invert" it against 255
		$sqrt = intval(255 - ceil(sqrt($part1 * $part2)));

		// Encode to hex, pre-pad it with zeros and add to new hash
		$sqrtHash .= padHex($sqrt);
	} // END - for

	// "sqrt-hash" must have same length as input hash
	assert(strlen($sqrtHash) === strlen($hash1));

	// Hash reversed "sqrt-hash" again and return it
	return hashString(strrev($sqrtHash));
}

/**
 * Converts a number between 0 and 255 into a zero-padded hexadecimal string
 *
 * @param	$num	Number between 0 and 255
 * @return	$hex	Hexadecimal string, padded with zeros
 */
function padHex ($num) {
	// Must be a integer number and between 0 and 255
	assert(is_int($num));
	assert($num >= 0);
	assert($num <= 255);

	// Convert it
	$hex = str_pad(dechex($num), 2, '0', STR_PAD_LEFT);

	// ... and return it
	return $hex;
}

/*
 * Calculate "genesis" hashes, please note that these "genesis strings" are now
 * known to the public as you can read them here in source code and therefore I
 * will not use them for the real genesis hashes.
 */
$hashes = array(
	// A famous quote from Deus Ex 2 - Invisible War
	doublehashString('"Informations must be free." - AI Helios'),
	// My name + URL of my first StatusNet instance
	doubleHashString('Roland Haeder, http://status.mxchange.org'),
	// A famous quote from Linus Torwalds
	doubleHashString('"Software is like sex. Its better when its free." - Linus Torwalds'),
	// Possible truth ;-)
	doubleHashString('September 11 is a big lie.'),

	// GNU is not Uni*
	doubleHashString('GNU is Not Uni*.'),
	// WINE is not an emulator
	doubleHashString('WINE Is Not an Emulator.'),
	// FlightGear - Fly free!
	doubleHashString('FlightGear - Fly free!'),
	// Linus Torwalds Quote
	doubleHashString('Your code is shit.. your argument is shit.'),
);

// Calculate "modula hash" from 1st/4th and 2nd/3rd
$modulaHashes = array(
	// "Block" 0
	modulaHash($hashes[0], $hashes[3]),
	modulaHash($hashes[1], $hashes[2]),

	// "Block" 1
	modulaHash($hashes[4], $hashes[7]),
	modulaHash($hashes[5], $hashes[6]),
);

// Calculate "sqrt hash"
$sqrtHashes = array(
	sqrtHash($modulaHashes[0], $modulaHashes[1]),
	sqrtHash($modulaHashes[2], $modulaHashes[3])
);

// Calulcate modula hash
$modulaHash = modulaHash($sqrtHashes[0], $sqrtHashes[1]);

// Output results
print ('hashes=' . print_r($hashes, TRUE));
print ('modulaHashes=' . print_r($modulaHashes, TRUE));
print ('sqrtHashes=' . print_r($sqrtHashes, TRUE));
print ('modulaHash=' . $modulaHash . PHP_EOL);

// [EOF]
?>