The description seems curious. I'm not sure what the need for that would be? Retro-compat with existing stores/caches (but only in one direction) + mitigation a

The description seems curious. I'm not sure what the need for that would be? Retro-compat with existing stores/caches (but only in one direction) + mitigation against some collision attacks? hm I don't see the point. If you switch the hash function, I guess in the vast majority of cases you can switch it completely for something that is known to be really better, not a weird hack. Must fit a purpose in some Google software as a better than nothing quick&dirty temporary hack -- and I would not advice doing it in other contexts unless you know for sure you have no other choice.