Question

There’s a string, containing characters [a-zA-Z0-9]. This should be 26 * 2 + 10 = 62 possibilities in one character and 62^2 in two. What is the preferred way to increment a value of such a string, so that ‘aA’, becomes ‘aB’, etc.? Is there any built-in stuff in PHP, that can help?

I know you can increment a string, but that’s only lowercase letters. Essentially, the result should go from ‘a’ to ‘aa’ in 61 increments.

Answer 1

The @simshaun dont work for me. I check the documentation and I found base_convert that can work for you (on base 35) and a comment of “francesco[at]paladinux.net” with a function to work on base65.

so the solution can be:

convert to b10 -> increment +1 -> convert base 65

EDIT 1

talking about convert I think to base64 coding so I wrote this 2 funcs using base64 encode/decode numbers.
Unfortunately the charset used is a bit larger: [a-zA-Z0-9/+=], but using an internal function more efficent.

The Zero
0 is “AA==”

function nencode($in){
        $res ="";
        while(1){
                $b = $in & 0xff;
                $res = chr($b) . $res;

                if($in > 0xff){
                        $in = $in >> 8;
                } else {
                        break;
                }
        }
        return base64_encode($res);
}

function ndecode($in){

        $rv=0;
        $res =base64_decode($in);
        for($t = 0 ; $t < strlen($res) ; $t++){
                if($t>0){
                        $rv = $rv << 8;
                }
                $c = ord($res{$t});
                $rv |= $c;
        }
        return $rv;
}