Messages in this thread | | | Subject | Re: [RFC] B+Tree library V2 | From | Johannes Berg <> | Date | Thu, 08 Jan 2009 21:18:55 +0100 |
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On Thu, 2009-01-08 at 21:02 +0100, Jörn Engel wrote:
> > #define btree_for_each_key(head, geo, key, tmp) \ > > for (key = btree_last(head, geo), tmp = btree_get_prev_key(head, geo, key); > > key; key = tmp, tmp = btree_get_prev_key(head, geo, key)) > > [ Changed the function name above. It really isn't a lookup, it returns > a key, not a value. My fault. ]
Right.
> Looks correct otherwise. Probably needs a comment that without "tmp" we > would skip a 0 key. Or am I the only one who wants to simplify the code > before spotting this little subtlety?
I, uh, I didn't even realise that. I think the code for btree_last/btree_get_prev_key isn't correct as is since the 0 key is valid, but you can't tell whether it returned 0 because it didn't find anything, or because there was no more entry. Or am I missing something?
> > (and possibly some type-checking variants that hardcode the geo) > > > > Does that seem correct? And would it be possible to provide btree_last() > > that takes an void ** and fills it with the last entry, and the same for > > lookup_less(), so we can write btree_for_each_entry() too? > > Not sure what you mean. Something with the same effect as this? > > #define btree_for_each_val(head, geo, key, val) \ > for (key = btree_last(head, geo), \ > val = btree_lookup(head, geo, key); \ > val; \ > key = btree_get_prev_key(head, geo, key), \ > val = btree_lookup(head, geo, key))
Well, that does lots of lookups that don't seem necessary, since a function like btree_last should be able to return the value right away. Also, if it was
#define btree_for_each_val(head, geo, key, val) for (val = btree_last(head, geo, &key); val; val = btree_get_prev(head, geo, &key))
it would be more correct, I think?
johannes [unhandled content-type:application/pgp-signature] | |