[KMag]

PrefixVarint isn't open-source, but the encoding is trivial.

PrefixVarints are a folk theorem of Computer Science, (re-)invented in many times and places.

I actually coded it up once in Python and once in C before joining Google, and was chatting with an engineer, complaining about the Protocol Buffer varint encoding. The person I was complaining to, said "Yea, Doug Rhode did exactly that, called it PrefixVarint. He benchmarked it much faster."