PATCH: Correct b?branch for negative offset branches

[Mark Cave-Ayland]

Hi everyone,

Please find enclosed a patch against current SVN that allows b?branch to 
work for negative offset branches. With this patch applied, the 
following output can be seen under openbios-unix on x86 (32-bit):

For the non-branch case (flags is set to -1):

0 > here  ok
1 > 10 c, ff c, ff c, ff c, ff c,  ok
1 > b1 c,  ok
1 > 10 c, aa c, aa c, aa c, aa c,  ok
1 > 9d c,  ok
1 > 02 c, 16 c,  ok
1 > 14 c, f7 c,  ok
1 > 02 c, 16 c,  ok
1 > 00 c,  ok
1 > dup 1 byte-load
byte-load: exception caught!
  ok

For the branch case (flags is set to 0):

0 > here  ok
1 > 10 c, 00 c, 00 c, 00 c, 00 c,  ok
1 > b1 c,  ok
1 > 10 c, aa c, aa c, aa c, aa c,  ok
1 > 9d c,  ok
1 > 02 c, 16 c,  ok
1 > 14 c, f7 c,  ok
1 > 02 c, 16 c,  ok
1 > 00 c,  ok
1 > dup 1 byte-load -55555556
byte-load: exception caught!
  ok

Note that in terms of docbranch, the branch action being taken is 
actually the opposite to what you may expect due to the use of 
setup-tmp-comp (hence the extra invert is required). So as an example, 
if flags is set to 0 then docbranch does not change the PC, and so we 
execute the contents of the temporary buffer which contains everything 
from b(<mark) to b(>resolve). On the other hand, if flags is non-zero 
then docbranch will branch back to the b(>resolve), and so the temporary 
buffer contents are ignored.

AFAICT the behaviour is correct from the above examples, but again I'd 
suggest that someone with more OpenBIOS experience should verify to make 
sure that this is the right approach.

ATB,

Mark.

[Blue Swirl]

On 4/6/09, Mark Cave-Ayland  wrote:
> Hi everyone,
>
> Please find enclosed a patch against current SVN that allows b?branch to
> work for negative offset branches. With this patch applied, the following
> output can be seen under openbios-unix on x86 (32-bit):
>
> For the non-branch case (flags is set to -1):
>
> 0 > here  ok
>  1 > 10 c, ff c, ff c, ff c, ff c,  ok
>  1 > b1 c,  ok
>  1 > 10 c, aa c, aa c, aa c, aa c,  ok
>  1 > 9d c,  ok
>  1 > 02 c, 16 c,  ok
>  1 > 14 c, f7 c,  ok
>  1 > 02 c, 16 c,  ok
>  1 > 00 c,  ok
>  1 > dup 1 byte-load
>  byte-load: exception caught!
>   ok
>
> For the branch case (flags is set to 0):
>
> 0 > here  ok
>  1 > 10 c, 00 c, 00 c, 00 c, 00 c,  ok
>  1 > b1 c,  ok
>  1 > 10 c, aa c, aa c, aa c, aa c,  ok
>  1 > 9d c,  ok
>  1 > 02 c, 16 c,  ok
>  1 > 14 c, f7 c,  ok
>  1 > 02 c, 16 c,  ok
>  1 > 00 c,  ok
>  1 > dup 1 byte-load -55555556
>  byte-load: exception caught!
>   ok
>
> Note that in terms of docbranch, the branch action being taken is actually
> the opposite to what you may expect due to the use of setup-tmp-comp (hence
> the extra invert is required). So as an example, if flags is set to 0 then
> docbranch does not change the PC, and so we execute the contents of the
> temporary buffer which contains everything from b(<mark) to b(>resolve). On
> the other hand, if flags is non-zero then docbranch will branch back to the
> b(>resolve), and so the temporary buffer contents are ignored.
>
> AFAICT the behaviour is correct from the above examples, but again I'd
> suggest that someone with more OpenBIOS experience should verify to make
> sure that this is the right approach.

Thanks, applied.