The following two functions are an alphanumeric encoder and
decoder respectively. The intent of
the first function is to take a base 10 number and encode it using some character
set. It is hardcoded to use a charset of
“1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ”.
Because there are 36 characters in this character set, the encoder
effectively becomes a base 10 to base 36 encoder by default. But you can either alter the default encoding
string or pass in the alphabet you want to use as a second argument and encode
the base 10 number to any base you desire. The second function reverses the process.
I have tested both functions quite extensively, and they both appear to work flawlessly.
/**
* Encode a base 10 number into some alternate base
*
* @param int $num
* @param string $alphabet
* @return string $alphaNum
*/
public static function alphaEncode($num, $alphabet=null) {
$result = '';
if (!$alphabet) {
$alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
}
$alphabet = str_split($alphabet);
if ($num == 0) {
return $alphabet[0];
}
$base = count($alphabet);
while ($num > 0) {
$remainder = $num % $base;
$num = floor($num / $base);
$alphaNum = $alphabet[$remainder] .
$alphaNum;
}
return $alphaNum;
}
/**
* Decode an encoded number back into base 10
*
* @param string $alphaNum
* @param string $alphabet
* @return int $num
*/
public static function alphadDecode($alphaNum, $alphabet=null) {
$result = '';
if (!$alphabet) {
$alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
}
$alphabet = str_split($alphabet);
$base = count($alphabet);
$num = 0;
$idx = 0;
$charCount = strlen($alphaNum);
$charArray = str_split($alphaNum);
foreach ($charArray as $char) {
$power = ($charCount - ($idx + 1));
$charIndex = array_search($char,
$alphabet);
$num += $charIndex * pow($base,
$power);
$idx++;
}
return $num;
}
