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?

use bignum;

my $var1 = 0x0000805063008357 ;
my $var2 = 0x042426FFFFFFFFFF ;

my $result =  $var1 ^ $var2;
printf "0x%016x\n",$result;
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0x00000000ffffffff
[download]

Which goes to show that printf does not support big ints.

You could write

print $result->as_hex();
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because, with the bignum pragma in effect, the numbers are upgraded to Math::BigInt objects which have the as_hex() method (among others).

And to get rid of the "Hexadecimal number > 0xffffffff non-portable" warning, you could say

my $var1 = hex("0x0000805063008357");
[download]

(hex() would need to be imported for perls before 5.9.4)

For really large values you can use the (core) module Math::BigInt:

#!/usr/bin/perl -l
use strict;
use warnings;
use Math::BigInt;

my $x = Math::BigInt->new("0x00008050630083570000805063008357000080506
+3008357");
my $y = Math::BigInt->new("0x042426FFFFFFFFFF042426FFFFFFFFFF042426FFF
+FFFFFFF");

print $x->bxor($y)->as_hex();   # 0x424a6af9cff7ca80424a6af9cff7ca8042
+4a6af9cff7ca8
[download]