Integer -> Alphabet encoder: https://stackoverflow.com/questions/22043451

alphabet-encoder.php

class AlphabetEncoder {
	private static $ALPHABET;
	private static $ENCODE_LENGTH;

	private static function populateAlphabet() {
		if (self::$ENCODE_LENGTH) return;
		for ($n = 48; $n < 58; $n++)
			self::$ALPHABET[] = chr($n);
		for ($n = 65; $n < 91; $n++)
			self::$ALPHABET[] = chr($n);
		for ($n = 97; $n < 123; $n++)
			self::$ALPHABET[] = chr($n);
		self::$ENCODE_LENGTH = count(self::$ALPHABET);
	}

	public static function encode($victim) {
		self::populateAlphabet();
		$list = [];
		do {
			$list[] = self::$ALPHABET[$victim % self::$ENCODE_LENGTH];
			$victim = floor($victim / self::$ENCODE_LENGTH);
		} while ($victim > 0);
		$list = array_reverse($list);
		return implode('', $list);
	}

	public static function decode($encoded) {
		self::populateAlphabet();
		$ret = 0;
		$c = '';
		for ($index = 0; $index < strlen($encoded); $index++) {
			$c = substr($encoded, $index, 1);
			$ret *= self::$ENCODE_LENGTH;
			$ret += array_search($c, self::$ALPHABET);
		}
		return $ret;
	}
}