Base10 to base64 url shortening

Question

I\'m coding an url shortener function for a project in which I\'m learning php, here is the code (btw I suppose that global here is not a good thing to do :P):<

Answer 1

Just a couple of little tweaks needed, the main two were to make the the alphabet zero indexed rather than one-indexed, and to subtract the remainder from the id before dividing

function shorten($id)
{
    $alphabet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-';
    $shortenedId = '';
    while($id>0) {
        $remainder = $id % 64;
        $id = ($id-$remainder) / 64;     
        $shortenedId = $alphabet{$remainder} . $shortenedId;
    };
    return $shortenedId;
}

and here's a further modified version which... well I just like

function shorten($id, $alphabet='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-')
{
    $base = strlen($alphabet);
    $short = '';
    while($id) {
        $id = ($id-($r=$id%$base))/$base;     
        $short = $alphabet{$r} . $short;
    };
    return $short;
}

EDIT: sorted concatenation to be the same as the OPs

Answer 2

You can use the pack.

$int = 1129717211140920362;

$byte = pack('J*', $int);    
echo base64_encode($byte); //= D62P0WqzFCo=

It will result in D62P0WqzFCo=, it is correct, because the $int is an int64 and uses 64 bits. The Base64 uses 6 bits for each character, so they need ~11 characters.

To decode use:

$base64 = 'D62P0WqzFCo=';

$byte = base64_decode($base64);
echo unpack('J*',  $byte)[1]; //= 1129717211140920362

It will return 1129717211140920362. ;)

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_{It was based in the answer on the Stackoverflow in Portuguese.}