This is thoughtless-patch to lua that keeps a length field in the C struct of the table. It behaves as the following:

• A length is kept in a new field of the table struct (intialized to 0)
• Length-operator/opcode return it
• The length is changed every time something is written in t[#t+1] (nil also).
• ipairs loops from 1 to this length, also if there are holes
• The table.setlen function can be used to set the value of the new field. It does not change anything else.

The execution time increases by ~1% (when updating the length) while the memory size increases by ~8% (when storing empty tables).