[OpenBIOS] [PATCH] Adds local variable support to OpenBIOS.

Segher Boessenkool segher at kernel.crashing.org
Tue Aug 28 08:40:19 CEST 2012

>>> +\ Sets the twelfth local variable's value
>>> +: Local11!	( x - )
>>> +	11 CELL * getBaseAddress + !
>>> +;
>> ...why stop at 11?
> As far as I know, Apple's code only uses two local variables at  
> most. I figured 12 local variables per word should be enough.

Apple's code uses a maximum of eight locals (and they actually
use (close to) that -- really badly factored code).

Neither 8 nor 12 is anywhere near close enough to allow compiled
C code to run.  Any implementation that limits the number of
allowed locals is only good for letting people who are not yet
comfortable with programming Forth code get something done.
Whether it is better to let them do that, or force them to learn
to use Forth properly first, is not something I want to get into
here ;-)

[SNIP a word of 30 lines, indented to hell and back, impossible
to read]

>> Factor this?  You shouldn't ever use a variable that is used as a  
>> temp
>> inside a word.
> I'm not sure why you suggest this. It is just such a pain having to  
> deal with the stack.

That's why you should factor it!  A normal word should deal with
maybe two or three data items only, and do only one thing.  The
main problem is coming up with good names for your words (thankfully
you do not have to do this for data items, because you do not use
locals); but then again, if it is hard to think of a good name
for a word, it probably does more than one thing.  So factor some
more :-)

>> alloc-mem is way too slow to be used on every function call.   
>> Statically
>> allocate a locals stack, or put it on an existing stack, or something
>> like that.
> I agree. That is why it is only used at compile time.

That wasn't clear to me.  Maybe you should put in some more comments?
A good thing to comment are your data structures and the global data,
often the words using that are clear then as well.


More information about the OpenBIOS mailing list