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

> 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?