Thanks! it reads like a 36-ary encoding of an IP address in host byte order, rather than network byte order, which is why it seems to jump around so much.

Interestingly, it encodes 0.0.0.0.xip.io as 0.xip.io , but then refuses to answer for 0.xip.io. Why isn't obvious to me from reading the code, perhaps some kind of overflow condition is triggered by the right shift.