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From: "brian m. carlson" <sandals@crustytoothpaste.net>
To: Jonathan Nieder <jrnieder@gmail.com>
Cc: git@vger.kernel.org, Duy Nguyen <pclouds@gmail.com>
Subject: Re: State of NewHash work, future directions, and discussion
Date: Tue, 12 Jun 2018 02:28:15 +0000
Message-ID: <20180612022815.GL38834@genre.crustytoothpaste.net> (raw)
In-Reply-To: <20180611190103.GB20665@aiede.svl.corp.google.com>

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On Mon, Jun 11, 2018 at 12:01:03PM -0700, Jonathan Nieder wrote:
> Hi,
> 
> brian m. carlson wrote:
> > I plan on introducing an array of hash algorithms into struct repository
> > (and wrapper macros) which stores, in order, the output hash, and if
> > used, the additional input hash.
> 
> Interesting.  In principle the four following are separate things:
> 
>  1. Hash to be used for command output to the terminal
>  2. Hash used in pack files
>  3. Additional hashes (beyond (2)) that we can look up using the
>     translation table
>  4. Additional hashes (beyond (1)) accepted in input from the command
>     line and stdin
> 
> In principle, (1) and (4) would be globals, and (2) and (3) would be
> tied to the repository.  I think this is always what Duy was hinting
> at.
> 
> All that said, as long as there is some notion of (1) and (4), I'm
> excited. :)  Details of how they are laid out in memory are less
> important.

I'm happy to hear suggestions on how this should or shouldn't work.  I'm
seeing these things in my head, but it can be helpful to have feedback
about what people expect out of the code before I spend a bunch of time
writing it.

> [...]
> > The transition plan anticipates a stage 1 where accept only SHA-1 on
> > input and produce only SHA-1 on output, but store in NewHash.  As I've
> > worked with our tests, I've realized such an implementation is not
> > entirely possible.  We have various tools that expect to accept invalid
> > object IDs, and obviously there's no way to have those continue to work.
> 
> Can you give an example?  Do you mean commands like "git mktree"?

I mean situations like git update-index.  We allow the user to insert
any old invalid value (and in fact check that the user can do this).
t0000 does this, for example.

> You can always use something like e.g. "doubled SHA-1" as a proof of
> concept, but I agree that it's nice to be able to avoid some churn by
> using an actual hash function that we're likely to switch to.

I have a hash that I've been using, but redoing the work would be less
enjoyable.  I'd rather write the tests only once if I can help it.
-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204

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  reply index

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-09 20:56 brian m. carlson
2018-06-09 21:26 ` Ævar Arnfjörð Bjarmason
2018-06-09 22:49 ` Hash algorithm analysis brian m. carlson
2018-06-11 19:29   ` Jonathan Nieder
2018-06-11 20:20     ` Linus Torvalds
2018-06-11 23:27       ` Ævar Arnfjörð Bjarmason
2018-06-12  0:11         ` David Lang
2018-06-12  0:45         ` Linus Torvalds
2018-06-11 22:35     ` brian m. carlson
2018-06-12 16:21       ` Gilles Van Assche
2018-06-13 23:58         ` brian m. carlson
2018-06-15 10:33           ` Gilles Van Assche
2018-07-20 21:52     ` brian m. carlson
2018-07-21  0:31       ` Jonathan Nieder
2018-07-21 19:52       ` Ævar Arnfjörð Bjarmason
2018-07-21 20:25         ` brian m. carlson
2018-07-21 22:38       ` Johannes Schindelin
2018-07-21 23:09         ` Linus Torvalds
2018-07-21 23:59         ` brian m. carlson
2018-07-22  9:34           ` Eric Deplagne
2018-07-22 14:21             ` brian m. carlson
2018-07-22 14:55               ` Eric Deplagne
2018-07-26 10:05                 ` Johannes Schindelin
2018-07-22 15:23           ` Joan Daemen
2018-07-22 18:54             ` Adam Langley
2018-07-26 10:31             ` Johannes Schindelin
2018-07-23 12:40           ` demerphq
2018-07-23 12:48             ` Sitaram Chamarty
2018-07-23 12:55               ` demerphq
2018-07-23 18:23               ` Linus Torvalds
2018-07-23 17:57             ` Stefan Beller
2018-07-23 18:35             ` Jonathan Nieder
2018-07-24 19:01       ` Edward Thomson
2018-07-24 20:31         ` Linus Torvalds
2018-07-24 20:49           ` Jonathan Nieder
2018-07-24 21:13           ` Junio C Hamano
2018-07-24 22:10             ` brian m. carlson
2018-07-30  9:06               ` Johannes Schindelin
2018-07-30 20:01                 ` Dan Shumow
2018-08-03  2:57                   ` Jonathan Nieder
2018-09-18 15:18                   ` Joan Daemen
2018-09-18 15:32                     ` Jonathan Nieder
2018-09-18 16:50                     ` Linus Torvalds
2018-07-25  8:30             ` [PATCH 0/2] document that NewHash is now SHA-256 Ævar Arnfjörð Bjarmason
2018-07-25  8:30             ` [PATCH 1/2] doc hash-function-transition: note the lack of a changelog Ævar Arnfjörð Bjarmason
2018-07-25  8:30             ` [PATCH 2/2] doc hash-function-transition: pick SHA-256 as NewHash Ævar Arnfjörð Bjarmason
2018-07-25 16:45               ` Junio C Hamano
2018-07-25 17:25                 ` Jonathan Nieder
2018-07-25 21:32                   ` Junio C Hamano
2018-07-26 13:41                     ` [PATCH v2 " Ævar Arnfjörð Bjarmason
2018-08-03  7:20                       ` Jonathan Nieder
2018-08-03 16:40                         ` Junio C Hamano
2018-08-03 17:01                           ` Linus Torvalds
2018-08-03 16:42                         ` Linus Torvalds
2018-08-03 17:43                         ` Ævar Arnfjörð Bjarmason
2018-08-04  8:52                           ` Jonathan Nieder
2018-08-03 17:45                         ` brian m. carlson
2018-07-25 22:56                 ` [PATCH " brian m. carlson
2018-06-11 21:19   ` Hash algorithm analysis Ævar Arnfjörð Bjarmason
2018-06-21  8:20     ` Johannes Schindelin
2018-06-21 22:39     ` brian m. carlson
2018-06-11 18:09 ` State of NewHash work, future directions, and discussion Duy Nguyen
2018-06-12  1:28   ` brian m. carlson
2018-06-11 19:01 ` Jonathan Nieder
2018-06-12  2:28   ` brian m. carlson [this message]
2018-06-12  2:42     ` Jonathan Nieder

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