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
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