Re: [Tack-devel] SBS instruction question

[David G. <dg...@co...>]

Is this for architectures where sizeof(ptr) != sizeof(int)? I believe the
m68k has a mode where it can operate like that. In this situation, if two
32-bit pointers are too far apart then the result can't be represented in a
16-bit int.

The em spec does say that you can only do pointer comparisons between
addresses in the same fragment.

On Sun, 23 Jun 2019 at 18:44, Carl Eric Codere via Tack-devel <
tac...@li...> wrote:

> Greetings,
>                Another interesting question on the SBS EM instruction.
>
> It seems that both em.p and the EM interpreter do overflow checking on the
> SBS (subtract pointer from pointer) instruction only when the word size is
> 16-bits. Should this be documented, and i guess if technically possible
> this should be the same for 32-bit pointers, right?
>
> Another simple question, is there a practical use-case where SBS is used
> where ptr1 - ptr2 where ptr2 is at higher address than ptr1? This gives a
> negative number and according to me should not be possible, right, but
> maybe i am missing something here... I am just curious to see if this is a
> valid use case.
>
> Thanks in advance,
> Carl
>
>
>
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