Large hex values with PHP hexdec

Question

I have some large HEX values that I want to display as regular numbers, I was using hexdec() to convert to float, and I found a function on PHP.net to convert that to decimal, but it seems to hit a ceiling, e.g.:

$h = 'D5CE3E462533364B';
$f = hexdec($h);
echo $f .' = '. Exp_to_dec($f);

Output: 1.5406319846274E+19 = 15406319846274000000

Result from calc.exe = 15406319846273791563

Is there another method to convert large hex values?

Answer 1

As said on the hexdec manual page:

The function can now convert values that are to big for the platforms integer type, it will return the value as float instead in that case.

If you want to get some kind of big integer (not float), you'll need it stored inside a string. This might be possible using BC Math functions.

For instance, if you look in the comments of the hexdec manual page, you'll find this note

If you adapt that function a bit, to avoid a notice, you'll get:

function bchexdec($hex)
{
    $dec = 0;
    $len = strlen($hex);
    for ($i = 1; $i <= $len; $i++) {
        $dec = bcadd($dec, bcmul(strval(hexdec($hex[$i - 1])), bcpow('16', strval($len - $i))));
    }
    return $dec;
}

(This function has been copied from the note I linked to; and only a bit adapted by me)

And using it on your number:

$h = 'D5CE3E462533364B';
$f = bchexdec($h);
var_dump($f);

The output will be:

string '15406319846273791563' (length=20)

So, not the kind of big float you had ; and seems OK with what you are expecting:

Result from calc.exe = 15406319846273791563

Hope this help ;-)
And, yes, user notes on the PHP documentation are sometimes a real gold mine ;-)