sub buk2 { $_[0] % 4 ? 0 : $_[0] % 100 ? 1 : not $_[0] % 400; }

            Rate browseruk    isleap   abigail      buk2
browseruk 82.8/s        --      -40%      -54%      -67%
isleap     138/s       67%        --      -24%      -45%
abigail    180/s      118%       31%        --      -28%
buk2       251/s      203%       82%       39%        --