PATCH: Fix various bugs in bbranch and b?branch implementations

[Mark Cave-Ayland]

Hi folks,

The attached patch fixes all of the various combinations of forwards and 
backwards branches for both bbranch and b?branch. With this patch 
applied to the latest openbios-svn, I can now run OpenBIOS to the point 
where it crashes out Qemu checked out a few weeks back. Nice :)

A couple of the fixes in this patch are for bugs introduced in my last 
commit. Whilst continuing to dig deeper into various bugs, I didn't 
appreciate at the time that it is not necessarily the description of the 
branch words that matters, more how they are tokenized by the Fcode 
evaluator.

For reference, here are the branch test cases I used to verify this 
behaviour:

\ Testing forward b?branch/bbranch (if/else/then equivalent)
\ Forth: 1 if .s else abort then
here
cc c,			\ offset16
a6 c,			\ 1 (change to a5 for 0 to pick the else clause)
14 c, 0 c, 7 c,		\ b?branch (if)
13 c, 0 c, 4 c,		\ bbranch  (else)
b2 c,			\ b(>resolve)
02 c, 16 c,		\ abort
b2 c,			\ b(>resolve)
9f c,			\ show stack
00 c,			\ end

\ Test backwards b?branch (begin/until equivalent)
\ Forth: 0 begin 1 + dup . dup 3 = until drop

here
cc c,			\ offset16
a5 c,			\ 0
b1 c,			\ b(<mark) (begin)
a6 c, 1e c,		\ +1
47 c,			\ dup
9d c, 92 c,		\ display the number
47 c,			\ dup
a8 c,			\ count to 3
3c c,			\ =
14 c, ff c, f7 c,	\ b?branch (until)
46 c,			\ drop (clear up stack)
0  c,			\ End

\ Test backwards bbranch (begin/while/repeat equivalent)
\ Forth: 3 begin dup . dup while 1 - repeat drop

here
cc c,			\ offset16
a8 c,			\ 3
b1 c,			\ b(<mark) (begin)
47 c,			\ dup
9d c, 92 c,		\ display the number
47 c,			\ dup
14 c, 00 c, 06 c,	\ b?branch (while)
a6 c, 1f c,		\ -1
13 c, ff c, f6 c,	\ bbranch (repeat)
b2 c,			\ b(>resolve)
46 c,			\ drop
00 c,			\ end

ATB,

Mark.

[Blue Swirl]

On 4/27/09, Mark Cave-Ayland  wrote:
> Hi folks,
>
> The attached patch fixes all of the various combinations of forwards and
> backwards branches for both bbranch and b?branch. With this patch applied to
> the latest openbios-svn, I can now run OpenBIOS to the point where it
> crashes out Qemu checked out a few weeks back. Nice :)
>
> A couple of the fixes in this patch are for bugs introduced in my last
> commit. Whilst continuing to dig deeper into various bugs, I didn't
> appreciate at the time that it is not necessarily the description of the
> branch words that matters, more how they are tokenized by the Fcode
> evaluator.

Thanks, applied.

With marTux 0.2 (Solaris derivative) I get:
Loading FCode image...
Loaded 5936 bytes
entry point is 0x4000
Evaluating FCode...
reserved fcode word.
Loading reserved fcode word.
reserved fcode word.
reserved fcode word.
FCode UFS Reader 1.13 05/06/08 08:30:31.
Unhandled Exception 0x0000000000000034
PC = 0x00000000ffd0e370 NPC = 0x00000000ffd0e374
Stopping execution