use strict;
use warnings;

my %hash_name = ( a => 1, b => 2, c => 3, d => 3 );

my %keys_of_max;
my $key_of_max;
my $numeric_cmp_result;

    $numeric_cmp_result = defined $key_of_max
        ? ( eval join '<=>', map { $hash_name{ $_ } } $_, $key_of_max 
+)
        : 1
    xor $numeric_cmp_result > 0 and %keys_of_max = ( $key_of_max = $_ 
+=> 1 )
    xor ( $numeric_cmp_result or $keys_of_max{ $_ } = 1 )
        for keys %hash_name;

print sort keys %keys_of_max;
[download]

Useless use of logical xor in void context at perlmonks_Max_Value.pl l
+ine 26.
cd
[download]