/f{exch 3 2 roll(.)search{f}if print print}def/g{(:)search{exch pop exch
g}{40}ifelse 1 index()eq{dup count 4 mul sub{(0.)print 1 sub}repeat}if exch dup
length 4{1 sub dup 0 ge{2 copy 1 getinterval}{(0)}ifelse print(.)print}repeat
def 4 sub}def 16{(%stdin)(r)file 40 string readline pop dup()ne{(.)search{f
print/.in-addr.arpa}{g pop/ip6.arpa}ifelse =}if}repeat
Note that non-ascii characters in the above source code will be escaped (such as \x9f).