use Data::Dumper;
use Benchmark qw(:all);

%ERRORS=('OK'=>0,'WARNING'=>1,'CRITICAL'=>2,'UNKNOWN'=>3,'DEPENDENT'=>4);

cmpthese(1000000, {
        'map' => sub {
            %ERRORS_TEXT = map { $ERRORS{$_} => $_ } keys %ERRORS;
        },
        'reverse' => sub {
            %ERRORS_TEXT = reverse %ERRORS;
        },
        'values' => sub {
            @ERRORS_TEXT{ values %ERRORS } = keys %ERRORS; 
        },
    }
);
__END__
First run:

Benchmark: timing 1000000 iterations of map, reverse, values...
       map: 27 wallclock secs (24.66 usr +  0.03 sys = 24.69 CPU) @ 40502.23/s (n=1000000)
   reverse: 10 wallclock secs ( 9.03 usr +  0.00 sys =  9.03 CPU) @ 110741.97/s (n=1000000)
    values:  8 wallclock secs ( 7.70 usr +  0.04 sys =  7.74 CPU) @ 129198.97/s (n=1000000)
            Rate     map reverse  values
map      40502/s      --    -63%    -69%
reverse 110742/s    173%      --    -14%
values  129199/s    219%     17%      --

Second run:
Benchmark: timing 1000000 iterations of map, reverse, values...
       map: 27 wallclock secs (24.49 usr +  0.03 sys = 24.52 CPU) @ 40783.03/s (n=1000000)
   reverse:  8 wallclock secs ( 8.54 usr +  0.02 sys =  8.56 CPU) @ 116822.43/s (n=1000000)
    values:  7 wallclock secs ( 7.55 usr +  0.01 sys =  7.56 CPU) @ 132275.13/s (n=1000000)
            Rate     map reverse  values
map      40783/s      --    -65%    -69%
reverse 116822/s    186%      --    -12%
values  132275/s    224%     13%      --

Third run:
Benchmark: timing 1000000 iterations of map, reverse, values...
       map: 26 wallclock secs (24.37 usr +  0.06 sys = 24.43 CPU) @ 40933.28/s (n=1000000)
   reverse: 11 wallclock secs ( 8.63 usr +  0.03 sys =  8.66 CPU) @ 115473.44/s (n=1000000)
    values:  9 wallclock secs ( 7.57 usr +  0.01 sys =  7.58 CPU) @ 131926.12/s (n=1000000)
            Rate     map reverse  values
map      40933/s      --    -65%    -69%
reverse 115473/s    182%      --    -12%
values  131926/s    222%     14%      --