parsing a hex string

/// int hex(string);
// if the script name "hex" collides with a variable or a resource somewhere
// just rename it

var result=0;

// special unicode values
var ZERO=ord("0");
var NINE=ord("9");
var A=ord("A");
var F=ord("F");

for (var i=1; i<=string_length(argument0); i++){
    var c=ord(string_char_at(string_upper(argument0), i));
    // you could also multiply by 16 but you get more nerd points for bitshifts
    result=result<<4;
    // if the character is a number or letter, add the value
    // it represents to the total
    if (c>=ZERO&&c<=NINE){
        result=result+(c-ZERO);
    } else if (c>=A&&c<=F){
        result=result+(c-A+10);
    // otherwise complain
    } else {
        // this will make the browser behave badly but you can leave it in
        // actual game maker if you want
        //show_error("bad input for hex(str)", true);
    }
}

return result;