my @values = @hash{ sort { $a <=> $b } keys %hash };

##</code><code>##

%hash = ();
@hash{ 0..@values-1 } = @values;

##</code><code>##

@hash{ keys(%hash), 0..keys(%hash)-1 } = ((undef) x keys(%hash), @hash{ sort { $a <=> $b } keys %hash });
delete @hash{ grep !defined $hash{$_}, keys %hash };

##</code><code>##

@hash{ 0..keys(%hash)-1 } = delete @hash{ sort { $a <=> $b } keys %hash };