base58.php

<?php

class base58
{
	static public $alphabet = "123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ";

	public static function encode($int) {
		$base58_string = "";
		$base = strlen(self::$alphabet);
		while($int >= $base) {
			$div = floor($int / $base);
			$mod = ($int - ($base * $div)); // php's % is broke with >32bit int on 32bit proc
			$base58_string = self::$alphabet{$mod} . $base58_string;
			$int = $div;
		}
		if($int) $base58_string = self::$alphabet{$int} . $base58_string;
		return $base58_string;
	}
	
	public static function decode($base58) {
		$int_val = 0;
		for($i=strlen($base58)-1,$j=1,$base=strlen(self::$alphabet);$i>=0;$i--,$j*=$base) {
			$int_val += $j * strpos(self::$alphabet, $base58{$i});
		}
		return $int_val;
	}
}

example.php

<?php

include("base58.php");

echo "http://flic.kr/p/" . base58::encode(3392387861) . "\n";

// outputs: http://flic.kr/p/6aLSHT

echo "3392387861 = " . base58::decode(base58::encode(3392387861)) . "\n";

// outputs: 3392387861 = 3392387861