flickr_photoid_to_shortcode.php

<?php

$photoid = <photoid>;
$alphabet = '123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ';

// function to encode from photoid to shortcode
function base_encode($photoid, $alphabet)
{
	$base_count = strlen($alphabet);
	$encoded = '';
	while ($photoid >= $base_count) {
		$div = $photoid/$base_count;
		$mod = ($photoid-($base_count*intval($div)));
		$encoded = $alphabet[$mod] . $encoded;
		$photoid = intval($div);
	}

	if ($photoid) $encoded = $alphabet[$photoid] . $encoded;

	return $encoded;
}


$shortcode = base_encode($photoid, $alphabet);

// function to decode from shortcode to photoid
function base_decode($shortcode, $alphabet)
{
	$decoded = 0;
	$multi = 1;
	while (strlen($shortcode) > 0) {
		$digit = $shortcode[strlen($shortcode)-1];
		$decoded += $multi * strpos($alphabet, $digit);
		$multi = $multi * strlen($alphabet);
		$shortcode = substr($shortcode, 0, -1);
	}

	return $decoded;
}

?>