Those hex constants represent 64-bit integers. You are using a version of Perl that can only handle 32-bit integers.

Several possibilities exist.

1. Upgrade to a 64-bit Perl:

   $var1 = 0x0000805063008357 ;;
   Hexadecimal number > 0xffffffff non-portable at (
   
   $var2 = 0x042426FFFFFFFFFF;;
   Hexadecimal number > 0xffffffff non-portable at (
   
   printf "0x%0x\n", $var1 ^ $var2;;
   0x424a6af9cff7ca8
   [download]

   The non-portable warnings are just a stupid annoyance that can be suppressed.

2. Manipulate the hex values as strings:

   $str2 = '042426FFFFFFFFFF';;
   
   $str1 = '0000805063008357';;
   
   print unpack 'H*', pack( 'H*', $str1 ) ^ pack('H*', $str2 );;
   0424a6af9cff7ca8
   [download]

   Whether that is useful will depend on how you are going to utilise the result?

3. (Re-)compile your 32-bit version of Perl with use64bitint=define.

   That allows a 32-bit perl to manipulate 64-bit numbers, though you'd probably get those annoying 'non-portable' warnings.

As always, the right solution for your purpose will depend heavily upon that purpose?