Re: [PATCH] Put sha1dc on a diet

From: Jeff King <peff@peff.net>
Date: Mar 13, 2017, 21:00 UTC
Message-ID: <20170313210023.bumtp6wyw6blmymp@sigill.intra.peff.net>
In-Reply-To: <161775901.3349663.1489438074825.JavaMail.zimbra@cwi.nl>

On Mon, Mar 13, 2017 at 09:47:54PM +0100, Marc Stevens wrote:

> Linus:
> I would be surprised, the dependencies should be automatically determined.
> 
> BTW Did you make local changes to this perf branch?

I can reproduce it with:

  cd sha1collisiondetection
  git clean -dqfx ;# make sure we are starting from scratch

  git checkout 9c8e73cadb35776d3310e3f8ceda7183fa75a39f
  make
  bin/sha1dcsum $file

  git checkout 55d1db0980501e582f6cd103a04f493995b1df78
  make
  bin/sha1dcsum $file

The final call to sha1dcsum will report a collision, even though the first one did not.

It also reproduces with the original snippet I posted. I didn't notice because I was just collecting the timings then (and I originally noticed the problem on the versions I had pulled into Git, where it works as expected; but then I am just pulling in the two source files, without all of the libtool magic).

-Peff