my ($idx, @array, $a_big_num, $some_data);

# Store the data
$idx = map_func($a_big_num);
$array[$idx] = $some_data;

# Fetch the data
$idx = map_func($a_big_num);
$some_data = $array[$idx];

##</code><code>##

my (%hash, $a_big_num, $some_data);

# Store
$hash{$a_big_num} = $some_data;

# Fetch
$some_data = $hash{$a_big_num};

##</code><code>##

sub map_func { return 7 }

##</code><code>##

sub map_func {
   state %indexes;
   state $idx;
   my $a_big_num = shift;
   return $indexes{$a_big_num} if exists $indexes{$a_big_num};
   die "Ran out of slots!" if keys %indexes > 1000;
   return $indexes{$a_big_num}=$idx++;
}