Re: [PATCH v2 2/4] Add structure representing hash algorithm

["brian m. carlson" <sandals@crustytoothpaste.net>]

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On Mon, Oct 30, 2017 at 04:36:15PM -0700, Brandon Williams wrote:
> On 10/28, brian m. carlson wrote:
> > Since in the future we want to support an additional hash algorithm, add
> > a structure that represents a hash algorithm and all the data that must
> > go along with it.  Add a constant to allow easy enumeration of hash
> > algorithms.  Implement function typedefs to create an abstract API that
> > can be used by any hash algorithm, and wrappers for the existing SHA1
> > functions that conform to this API.
> > 
> > Expose a value for hex size as well as binary size.  While one will
> > always be twice the other, the two values are both used extremely
> > commonly throughout the codebase and providing both leads to improved
> > readability.
> > 
> > Don't include an entry in the hash algorithm structure for the null
> > object ID.  As this value is all zeros, any suitably sized all-zero
> > object ID can be used, and there's no need to store a given one on a
> > per-hash basis.
> > 
> > The current hash function transition plan envisions a time when we will
> > accept input from the user that might be in SHA-1 or in the NewHash
> > format.  Since we cannot know which the user has provided, add a
> > constant representing the unknown algorithm to allow us to indicate that
> > we must look the correct value up.
> > 
> > Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> > ---
> > I believe I did get the format_id constant for SHA-1 right, but
> > sanity-checking would be appreciated.  We don't want another Referer
> > mess.
> > 
> >  cache.h     | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  sha1_file.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 98 insertions(+)
> > 
> > diff --git a/cache.h b/cache.h
> > index 6440e2bf21..9e9eb08f05 100644
> > --- a/cache.h
> > +++ b/cache.h
> 
> Maybe it would be good to place this interface in its own header file
> that way we can avoid cluttering cache.h with more stuff?

Sure, if you like.  It will end up needing to be included in cache.h
because of the blob and tree code, but I'm happy to split it out.
-- 
brian m. carlson / brian with sandals: Houston, Texas, US
https://www.crustytoothpaste.net/~bmc | My opinion only
OpenPGP: https://keybase.io/bk2204

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