Lua numbers are not boxed in the usual sense; they live in the Lua data stack (which leaves in the C heap, but this is not isomorphic to the Lua heap), are <i>not</i> accessed through a pointer, and do not put pressure on Lua's memory allocator and garbage collector.<p>LuaJIT 2's NaN tagging alone does not speed up the stock interpreter: <a href="http://article.gmane.org/gmane.comp.lang.lua.general/44823" rel="nofollow">http://article.gmane.org/gmane.comp.lang.lua.general/44823</a>.