Table performance

[Jack Christensen <jack@...>]

I'm trying to do as much as possible in Lua before I run into 
performance problems and have to drop back to C++. As part of the tests 
I was running I came across some surprising (to me anyway) results.

Am I doing something wrong or is it rather expensive to access to a table?

The following two blocks for code are identical except that one loop has 
two table accesses in it. The one with tables runs at less then half the 
speed.

local x, y, i = 0, 3, 0
while i < 500000 do
   x = i * y
   i = i + 1
end

local t = { x = 0, y = 3 }
local i = 0
while i < 500000 do
   t.x = i * t.y
   i = i + 1
end

I also tried binding a simple C++ class with luabind and running the 
equivalent loop. It was about 10 times slower than the table loop above.

Jack