How to convert uuid v4 of php into two 64 bit integers

Question

Example: Uuid generated from v4 of php : 8bc278cb-2fb6-413b-add6-8ba39bf830e8

I want to convert this into two 64 bit integers.

I've tried using hexdec of php but it's return value is of numbers. I want datatype integer.

Interestingly :

I have tried using hexdec with the above uuid and used this output to dechex. Some how, not getting the same value?

Any insights into this will be appreciated.

Random UUID (v4) has 2^122 combinations in total. While 64bit integer has, well, 2^64 combinations. It doesn't seems possible for the later to contain all possible data in the prior one. — Koala Yeung, Oct 05 '16 at 07:37
https://en.wikipedia.org/wiki/Universally_unique_identifier#Random_UUID_probability_of_duplicates — Koala Yeung, Oct 05 '16 at 07:37
[Here](https://stackoverflow.com/questions/56786533/how-to-convert-byte-array-to-float-in-php) is how to convert byte array into float in PHP. — Syed Azhar Abbas, Jun 27 '19 at 08:15

score 5 · Answer 1 · edited May 23 '17 at 11:46

UUID is a 128bit data type. Excluding the 6 reserved bits, there are 122 data bits in it. Makes it impossible to fully convert any UUID to a 64bit integer. You'll at least need to store it as 2 64bit numbers or 4 32bit numbers.

You can unpack the UUID into binary, then unpack it as 4 32bit unsigned character:

function uuidToHex($uuid) {
    return str_replace('-', '', $uuid);
}

function hexToUuid($hex) {
    $regex = '/^([\da-f]{8})([\da-f]{4})([\da-f]{4})([\da-f]{4})([\da-f]{12})$/';
    return preg_match($regex, $hex, $matches) ?
        "{$matches[1]}-{$matches[2]}-{$matches[3]}-{$matches[4]}-{$matches[5]}" :
        FALSE;
}

function hexToIntegers($hex) {
    $bin = pack('h*', $hex);
    return unpack('L*', $bin);
}

function integersToHex($integers) {
    $args = $integers; $args[0] = 'L*'; ksort($args);
    $bin = call_user_func_array('pack', $args);
    $results = unpack('h*', $bin);
    return $results[1];
}

$uuid = '1968ec4a-2a73-11df-9aca-00012e27a270';
var_dump($uuid);

$integers = hexToIntegers(uuidToHex('1968ec4a-2a73-11df-9aca-00012e27a270'));
var_dump($integers);

$uuid = hexToUuid(integersToHex($integers));
var_dump($uuid);

It will returns

string(36) "1968ec4a-2a73-11df-9aca-00012e27a270"
array(4) {
  [1]=>
  int(2764998289)
  [2]=>
  int(4245764002)
  [3]=>
  int(268479657)
  [4]=>
  int(120222434)
}
string(36) "1968ec4a-2a73-11df-9aca-00012e27a270"

$integers is an array 4 32bit numbers that represents the hex.

Reference

Stack Overflow: 16 bytes binary form of canonical uuid representation in php
Stack Overflow: How to convert byte array to integer in php?
PHP Manual: pack()

I have tried re-forming the hex from the two 64 bit integers that your function returns. It's not matching ```1968ec4a-2a73-11df-9aca-00012e27a270```. Ideally it should match. — riser101, Oct 05 '16 at 08:31
Can you show me the code you use to re-format the 2 64bit integer into hex? — Koala Yeung, Oct 05 '16 at 08:37

score 3 · Answer 2 · answered Mar 01 '17 at 21:40

While it's common in other languages (like Java) to get the least significant and most significant bits of a UUID as two unsigned 64-bit integers, PHP has trouble with this because all integers in PHP are signed. Even if using a 64-bit build of PHP, you will run into integer overflows when trying to get a real integer value of the least or most significant bits of a UUID.

The maximum integer value on 64-bit PHP is 9,223,372,036,854,775,807, while an unsigned 64-bit integer has a max value of 18,446,744,073,709,551,615. A UUID as two 64-bit integers needs to support values up to 18,446,744,073,709,551,615.

As an earlier answer mentioned, it might be better to split up the UUID into four unsigned 32-bit integers, if you need to split it up like that. (The max value of an unsigned 32-bit integer is 4,294,967,295, which 64-bit PHP can support.)

If you're simply interested in storing a UUID in a more optimized way, you can convert it to a 16-byte binary string:

$uuid = '1968ec4a-2a73-11df-9aca-00012e27a270';

$binaryUuid = hex2bin(str_replace('-', '', $uuid));

How to convert uuid v4 of php into two 64 bit integers

2 Answers2

Reference