really fast metatable lookup in C

[Asko Kauppi <asko.kauppi@...>]

Based on the enum/int32 implementation for Lua, I'm in the need for an 
extremely fast integer -> metatable lookup on the C side.
Currently, I use 'glua_meta_nn' keys into the registry, but there must 
be a better way.
Could I, say, have a set of some 1000 :) virtual indices s.a. 
'REGISTRYINDEX' all for my own need. I could maintain that range by 
myself (store table references there, in neat order) as long as it 
would be sure no-one else is dealing with those 'slots'.
Does Lua already provide this, or could such a range be considered for 
the future?
-ak