Am Sonntag, 22. April 2007 09:11 schrieb Patrick Rutkowski:
> I think Leo would be the best person to go to for an explanation,
> especially if you plan to dramatically rework the code.
> >> This is where I start not to understand. Why reg_alloc + 7? Why
> >> shift left
> >> and right by 3?
> >
> > I'm not sure if it is actually doing anything that needs to be that
> > complicated to code that way. It could be able to be written as:
> >
> > const int slot = (reg_alloc + 7) / 8; /* divide by eight for
> > some reason and round up on remainder */
> > reg_alloc = slot * 8; /* reg_alloc is now evenly divisible by 8 */
Sure. It's just rounding up to the next multpile of 8.
> > ... Now, slot is multiplied by sizeof(void*) later on,
> > which may be why it's divided by eight in the first place.
The rounding up happens to reduce the size of the free_list array.
> > The n = slot + 1 I find a little odd, because the number is already
> > rounded up, so it's rounding up and then adding an extra place of
> > memory.
This is for the extension of the free_list.
> >> I do understand the purpose of the resizing code, but not how slot
> >> relates to
> >> it:
> >>
> >> if (slot >= interp->ctx_mem.n_free_slots) {
Well, if slot is beyond the end of the list, it's resized.
> > The *(void **) has been confusing me for a long time.
The free list per size (i.e. one slot) is a linked list of pointers.
> >> I'd like to find a simpler scheme, if it's possible. Otherwise,
> >> I'd like to
> >> figure out what's going on so we can at least explain it somehow.
Why? This is all rather straight-forward and can be found in any memory
allocator e.g. ins smallobjects.
leo
