From: Jeff King <peff@peff.net>
Date: Sat, 25 Jan 2020 19:55:15 GMT
Subject: Re: [PATCH 1/4] merge-recursive: silence -Wxor-used-as-pow warning
Message-ID: <20200125195515.GB5519@coredump.intra.peff.net>
In-Reply-To: <xmqq4kwjcupj.fsf@gitster-ct.c.googlers.com>

On Sat, Jan 25, 2020 at 09:27:36AM -0800, Junio C Hamano wrote:

> > So let's keep the bit-flipping, but let's also put it behind a named
> > function, which will make its purpose a bit clearer. This also has the
> > side effect of suppressing the warning (and an optimizing compiler
> > should be able to easily turn it into a constant as before).
> 
> OK.  Now I see you named it flip_stage(), which is even better than
> "the-other-side" above.  Makes sense.
> 
> I still think ((2 + 3) - two_or_three_to_be_flipped) easier to
> reason about than the bit flipping, as the implementation detail,
> though.

Yeah, the existing one relies on the coincidence that the two stages
differ by a single bit (in another universe, they could well be stages
"3" and "4").

I don't overly care on the implementation either way, since it's now
hidden in the helper. I mostly chose the bit-flip to match the existing
code, but I'd be happy to change it. Other people who actually work on
merge-recursive may have other opinions, though.

-Peff