use strict;
use warnings;

my %hash = (one => 1, two => 2, three => 3);
my @keys = sort {$hash{$a} <=> $hash{$b}} keys %hash;

print "$_ => $hash{$_}  " for @keys;
print "\n";
@hash{@keys} = @hash{reverse @keys};
print "$_ => $hash{$_}  " for @keys;

##</code><code>##

one => 1  two => 2  three => 3  
one => 3  two => 2  three => 1