[OpenBIOS] $find

[Stefan Reinauer]

* Stefan Reinauer <stepan at suse.de> [020625 13:00]:
> 0 > s" constant" $find   ok
> 3 > .s  120019b88 0 -1  ok

> Our definition seems to be wrong:
> col($FIND LAST @ >R 2DUP R@ COMP-WORD ?BRANCH(9) 2DROP R> DUP 
>     >XCODE SWAP CELL+ C@ TRUE EXIT R> @ ?DUP 0= ?BRANCH(-21) 2DROP FALSE)
> 
> what exactly does "SWAP CELL+ C@" do? should this not just be a NIP ?
 
Ah.. it fetches the word's flags, stupid me. This is not correct
according to the standard, though we do need this flag.

I have two things in mind:

* the word SEE
* the fcode evaluator

for the first one we need to be able to get to a word's header when we
have the execution token (xt). This seems impossible at the moment as
we have a variable header length 

for the second we need to know at least whether the word is compile-only
or immediate, given only the xt. Currently my implementation of the
evaluator keeps a lookup table containing of xts for every word
available in fcode, using the fcode# as an index in this table. 
This is created via
' end0 ,
[..]

I wrote a little function for this problem, but it runs in O(N), linear
to the number of dictionary entries:

: xt>hdr ( xt -- addr-a )
  last @
  begin
    2dup >xcode = if
      nip exit
    then
    @ dup 0= until
  ;

This looks suboptimal, but I'm going to use it until something better
comes up.

Anny comments?

  Stefan

-- 
The x86 isn't all that complex - it just doesn't make a lot of
sense.          -- Mike Johnson, Leader of 80x86 Design at AMD
	                          Microprocessor Report (1994)
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