Base encoder with customisable alphabets

BaseX.php

<?php
class BaseX {

	/** RFC4648 Base62 */
	const BASE_64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

	/** RFC4648 "URL and Filename safe" Base64 */
	const URL_64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_=";
	
	/** URL and filename safe Base64 in UCA order */
	const UCA_64 = "-_0123456789aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ=";
	
	/** RFC4648 Base32 */
	const BASE_32 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=";
	
	/** Nice human readable Base32 alphabet */
	const CROCKFORD_32 = "0123456789ABCDEFGHJKMNPQRSTVWXYZ=";
	const CROCKFORD_32_DECODER = "oOiIlL001111"; // nice fault tolerance
	
	/** RFC4648 "Extended Hex" alphabet */
	const HEX_32 = "0123456789ABCDEFGHIJKLMNOPQRSTUV=";
	
	static function bits($l) {
		return (int) floor(log($l) / log(2));
	}
	
	static function encode($i, $charset, $pad=0) {
		$l = strlen($charset);
		$n = self::bits($l);
		$mask = $l - 2;
		
		$r = ($i == 0) ? $charset{0} : "";
		while($i) {
			$j = $i & $mask;
			$r = $charset{$j} . $r;
			$i >>= $n;
		}
		
		if($pad) {
			$j = $pad - strlen($r);
			if($j) $r = str_repeat($charset{0}, $j) . $r;
		}
		
		return $r;
	}
	
	static function decode($data, $charset) {
		$l = strlen($charset);
		$n = self::bits($l);
	
		$result = 0;
		$c = strlen($data);
		for($i=0; $i<$c; $i++) {
			if($data{$i} == $charset{$l-1}) continue; // padding
			if($i > 0) $result <<= $n;
			$result |= strpos($charset, $data{$i});
		}
		return $result;
	}
	
	static function normalize($data, $decoder=null) {
		$data = strtoupper($data);
		if($decoder) {
			$p = strlen($decoder)/2;
			$data = strtr($data, substr($decoder, 0, $p), substr($decoder, $p));
		}
		return $data;
	}
	
	static function validate($input, $charset) {
		$enc = self::encode($input, $charset);
		$dec = self::decode($enc, $charset);
		//printf("%6d -> %4s -> %6d\n", $input, $enc, $dec);
		assert($dec === $input);
	}
}

if(realpath($_SERVER['SCRIPT_FILENAME']) != __FILE__) return;

// basic tests
$testset = array(0, 23, 496, 1024, 753812);

foreach($testset as $i) {
	BaseX::validate($i, BaseX::BASE_32);
	BaseX::validate($i, BaseX::CROCKFORD_32);
	BaseX::validate($i, BaseX::BASE_64);
	BaseX::validate($i, BaseX::UCA_64);
	assert(strtoupper(base_convert($i, 10, 32)) == BaseX::encode($i, BaseX::HEX_32));
}
assert(BaseX::decode(BaseX::normalize('qo4m', BaseX::CROCKFORD_32_DECODER), BaseX::CROCKFORD_32) == 753812);