How to convert a hexadecimal value into a signed integer in PHP?

Question

I am trying to convert a hex string into a signed integer.

I am able to easily transfer it into an unsigned value with hexdec() but this does not give a signed value

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 be 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 ;-)

Answer 2

Check out this comment via php.net:

hexdec() returns unsigned integers. For example hexdec("FFFFFFFE") returns 4294967294, not -2. To convert to signed 32-bit integer you may do:

<?php
echo reset(unpack("l", pack("l", hexdec("FFFFFFFE"))));
?>