Re: Discussing Lua compiling

[Marc Balmer <marc@...>]

Comment inline...

> I have been working with Lua on a PC, mainly for some initial project
> work. Ultimately I will want to move some of the code I have been
> writing to an embedded system with a Coldfire Processor (This is a
> Freescale, big endian CPU).
>  
> It got me thinking about cross compiling on the PC for the Coldfire
> processor, this raised a bunch of questions, see below, hopefully I can
> get a few answers here.
>  
> Q1)  What approx performance benefit should I expect in using a byte
> code version of a program rather than the source code version ? I did a
> quick test on the PC, my test program shrunk from 91k down to 59k when I
> ran it through luac. So that will save a few mS, just moving the file
> around, reading it etc. Am I correct in assuming when a Lua Src program
> runs, it first compiles to byte code and then once that stage completes,
> you would expect identical execution times between a byte code version
> and a source version ? So the execution time saving is just the initial
> one off compile time ?

Yes.

> Q2) My first attempt at compiling went from 91k to 92k as I didnt use
> the -s option. I was surprised by the fact that without the -s it
> includes debug info in the output file. Just intrigued to know what this
> debug info is, and what programs use it ? Any explanation or links to
> read up on this ? 
>  
> Q3) Some Googling told me that some cross compiler programs have been
> attempted before. What I found looked quite old, so I am not sure how
> well they work with current Lua version ?  Is there a good reliable
> program I can be using now to achieve a PC based cross compile ? 
> I havent double checked yet but I think my embedded CPU has identical C
> data sizes compared to a WIN32 compile, so my cross compile would just
> need to cope with the little endian to big endian switch.
>  
> Q4) I found a reference from one of the Lua authours mentioning he had
> thought about making cross compilation a Luac feature. This would be a
> useful feature for me personally, is this a likely addition for Lua V5.2
> or even V5.3 ?
>  
> Q5) If there are no other options, I guess I could look at making my own
> cross compiling version, but at the moment I have no understanding of
> the bytecode file format. Any links please that I can read up on how
> this all works ?
>  
> Thanks for any help
>  
> Regards Geoff 
>  
>