On Wed, Jan 13, 2021 at 10:46:57PM -0800, Junio C Hamano wrote: > Taylor Blau <me@xxxxxxxxxxxx> writes: > > > +/* > > + * offset_to_pack_pos converts an object offset to a pack position. This > > + * function returns zero on success, and a negative number otherwise. The > > + * parameter 'pos' is usable only on success. > > + * > > + * If the reverse index has not yet been loaded, this function loads it lazily, > > + * and returns an negative number if an error was encountered. > > It is somewhat strange to see a function that yields a non-negative > "position" on success and a negative value to signal a failure to > have a separate pointer to the location to receive the true return > value. Do we truly care the upper half of "uint32_t" (in other > words, do we seriously want to support more than 2G positions in a > pack)? I don't think that we care about that as much as we do about potential misuse of a signed return value. There are indeed a couple of spots where a potential negative return value is ignored, and then used to lookup an object in a pack, or some such. And that's part of the goal of this API: we have strict guidelines about when the output parameter is and isn't usable. That makes it more difficult to accidentally use an uninitialized value / negative number. > What I'm trying to get at is that [...] is more natural than [...] but > now I wrote it down and laid it out in front of my eyes, the latter > does not look too bad. OK, good :-). > ... later comes back after reading through the series ... > > The new callers all looked quite nice to eyes. Because we > discourage assignment inside if() condition, the converted > result does not make the code more verbose than the > original. In fact, it makes it even clearer that we are > checking for an error return from a function call. > > Quite nice. Thank you :-D. > > + * This function runs in time O(log N) with the number of objects in the pack. > > Is it a good idea to commit to such performance characteristics as a > promise to callers like this (the comment applies to all three > functions)? > > It depends on how a developer is helped by this comment when > deciding whether to use this function, or find other ways, to > implement what s/he wants to do. I don't mind it. If they all had the same performance characteristics, I wouldn't be for it, but since they don't, I think that it's good to know. Peff suggested this back in [1]. Thanks, Taylor [1]: https://lore.kernel.org/git/X%2F1guCOGWybOzIS7@xxxxxxxxxxxxxxxxxxxxxxx/
