use Algorithm::Loops 'MapCarMin';
%hash = MapCarMin {@_} [ 0 .. keys %hash ],
    [ @hash{ sort {$a<=>$b} keys %hash } ];

##</code><code>##

%hash = map {
    ref($_) && $_ == \$hash{''}
        ?   ( delete $hash{''} )[1..0]
        :   ( ++$hash{''}, $_ )
}   @hash{ sort {$a<=>$b} keys %hash }, \$hash{''};

##</code><code>##

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