Re: State machines and goto (Was: Next Version of Lua?)

[David Given <dg@...>]

Robert Raschke wrote:
[...]
> I find using a "machine state" Lua table that you can pass around to be 
> pretty ideal.

This means looking stuff up dynamically from the table, which gives you 
an order of magnitude performance hit. Table lookups are *slow*. Simply 
moving the program counter from one bytecode address to another is fast. 
Plus using table lookups means that (assuming I've understood you 
correctly), the handler for each state needs to be a function, which 
means you run into the problem of efficiently sharing data between the 
handlers.

As an example, Clue used to run C code converted to Lua at about 30% of 
the speed of native when using goto. (With LuaJit.) When I took out the 
foul hack I was using to patch the bytecode to add the gotos, and 
started using a state variable and if..then..else chain, the performance 
dropped by 2/3.

--
David Given
dg@cowlark.com