Re: [PATCH v2 01/20] pack-revindex: introduce a new API

Jeff King [off-list ref] writes:

On Thu, Jan 14, 2021 at 12:06:20PM -0500, Taylor Blau wrote:

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+ * 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].

Yeah, I asked for this. As somebody who has frequently worked on the
code which accesses the revindex (mostly bitmap stuff), I found it
useful to understand how expensive the operations were.  However, I also
know what their runtimes are at this point, and it is not like somebody
interested cannot look at the implementation. So it may not be that
important.

So I do still think it is useful, but if somebody feels strongly against
it, I don't mind it being removed.

That won't be me.  It's not like you'd use pack_pos_to_index()
combined with pack_pos_to_offset() instead of offset_to_pack_pos()
because the latter is more expensive than using the other two
functions; the comment does not help those who want to know relative
performance of these functions for such a purpose.

I was just curious who the comments were meant to help, that's all.

Thanks.