How do I flip a byte array in PHP

Question

I'm trying to find a php equivalent for this js function below:

Original JS function:

function getAddrCheckSum(addr: Buffer, isContract? : boolean): Hex {
    const addrPre20 = addr.slice(0, 20);
    const _checkSum = blake2b(addrPre20, null, ADDR_CHECK_SUM_SIZE);
    const checkSum = Buffer.from(_checkSum);

    if (!isContract) {
        return checkSum.toString('hex');
    }

    const newCheckSum = [];
    checkSum.forEach(function (byte) {
        newCheckSum.push(byte ^ 0xFF);
    });

    return Buffer.from(newCheckSum).toString('hex');
}

PHP implementation:

include_once('./lib/Blake2b.php');

function getAddrCheckSum($address, $isContract) {
    $ADDR_CHECK_SUM_SIZE = 5;

    $addrPre20 = substr($address, 0, 20);
    $blake2b = new Blake2b($ADDR_CHECK_SUM_SIZE); #<- blake object initialized with size=5
    $checkSum = $blake2b->hash($addrPre20);

    return $checkSum;
    if (!isContract) {
        return strval($checkSum);
    }

How can I rewrite this part below in php?

$newCheckSum = [];
//checkSum.forEach(function (byte) { 
// newCheckSum.push(byte ^ 0xFF);    
//});

return strval($newCheckSum);
}

Also, am I doing this right by replacing the js toString by php strval? and, do I need to find an equivalent of "Buffer.from(...,'hex')" for php instead of just assigning it to a variable?

Answer 1

bin2hex is your friend. Assuming that $checkSum is the hash in binary form and $isContract is boolean then just XOR $checkSum with the corresponding number of \xFF characters.
Here is a verbose version:

if (!$isContract)
{
 return bin2hex($checkSum);
}
else
{
 $newCheckSum = $checkSum ^ str_pad("", strlen($checkSum), "\xFF");
 return bin2hex($newCheckSum);
}

And a short one:

return bin2hex
(
  !$isContract ? $checkSum: $checkSum ^ str_pad("", strlen($checkSum), "\xFF")
);