Re: MPS: Forwording symbols

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Helmut Eller <eller.helmut@gmail.com> writes:

> On Fri, Jun 21 2024, Gerd Möllmann wrote:
>
>> Gerd Möllmann <gerd.moellmann@gmail.com> writes:
>>
>>> Sounds like a good plan to me.
>
> Some patches for this are below.

Thanks, pushed.

>>> Maybe we could also make predicate an enum at the same time? It need not
>>> be a Lisp_Object, and replacing it with an enum would make that clearer.
>
> This would require translating symbols to enums and back.  Or do you
> think about something else?

I haven't looked at all places. Could you please explain where that is
needed?

>> And if I had a wish free, I'd want the lispfwd with the void *, and
>> the structs, to be one struct with a type and a union.
>
> You mean lispfwd would require two words instead of one?  Would that work
> when swapping bindings in and out?

I was thinking of using 1 struct instead of 4, like so

  enum Lisp_Fwd_Pred
  {
    /* Something with values for the Lisp_Object predicate ... */
    ...  
  };

  struct Lisp_Fwd
  {
    enum Lisp_Fwd_Type : 8;
    enum Lisp_Fwd_Predicate predicate : 8;
    union
    {
      intmax_t *intvar;
      bool *boolvar;
      Lisp_Object *objvar;
      int offset;
    } u;
  };

Then removing the Lisp_Fwd_Bool etc. structures that currently exist and
replace this

  typedef struct { void const *fwdptr; } lispfwd;

which is just a void * with ornaments, with const struct Lisp_Fwd *.

> If we can use two words, then it would perhaps be possible to use
> pointers to the values directly instead of pointers to fwd objects?

That would make each symbol 1 word bigger. I wouldn't mind, but I
guess someone might find that questionable, unless we can prove
some speed advantage or so :-).