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exp: plumbling/hasher, Add ObjectHasher and ImmutableHash #920

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exp: plumbling/hasher, Add ObjectHasher and ImmutableHash #920

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Commits on Nov 10, 2023

  1. plumbing: format/config, Add ErrInvalidObjectFormat 

    Signed-off-by: Paulo Gomes <paulo.gomes@suse.com>
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    pjbgf committed Nov 10, 2023
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  2. plumbing: hash, Add SHA1 and SHA256 constants 

    Signed-off-by: Paulo Gomes <paulo.gomes@suse.com>
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    pjbgf committed Nov 10, 2023
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  3. plumbing: hash, Add ErrUnsupportedHashFunction 

    Signed-off-by: Paulo Gomes <paulo.gomes@suse.com>
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  4. plumbing: hash, Add hash.FromObjectFormat 

    The support for SHA256 will require the mapping between ObjectFormat and the
correct hash.Hash to be used.

Signed-off-by: Paulo Gomes <paulo.gomes@suse.com>
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    pjbgf committed Nov 10, 2023
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  5. exp: Introduces an experimental package 

    The new exp package will hold only experimental code, which may eventually
make its way to other parts of go-git.
One example of how it would be used is to support the breaking up of
changes required for things like SHA256. That feature would require
several packages to be changed, and introducing such changes to plumbing
in one go would be too disruptive.

The new changes would now be staged in the new package, and as they
mature they would be either moved into their target destination
(e.g. plumbing/hash), or removed if no longer needed.

As per caveat on the documentation, this package API may introduce
breaking changes to its subpackages in minor go-git releases,
therefore beware when depending on them.

Signed-off-by: Paulo Gomes <paulo.gomes@suse.com>
    @pjbgf
    pjbgf committed Nov 10, 2023
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  6. exp: plumbling/hasher, Add ObjectHasher and ImmutableHash 

    The introduction of both new types are a stepping stone to enable
SHA256 support concurrently - without the need for a build tag.

ImmutableHash provides a way to represent varied sized hashes (for SHA1
or SHA256) with a single type, while keeping similar performance of the
existing plumbing.Hash.

The names were picked in order to provide a clearer distinction on what
they do. ImmutableHash is the result of a hash operation and can't be
changed once calculated. ObjectHasher, adds the Git object header before
a normal hash operation that hash.Hash or plumbing/hash.Hash do.

The performance results shows that SHA1 operations could be slower,
however for SHA256 it can be over 3 times faster:

~Hasher/hasher-sha1-100B-16         	            2202226	     574.7 ns/op	 174.00 MB/s     272 B/op     7 allocs/op
~Hasher/objecthash-sha1-100B-16     	            1511851	     772.6 ns/op	 129.43 MB/s     272 B/op     9 allocs/op
~Hasher/objecthash-sha256-100B-16   	            5057584	     247.4 ns/op	 404.21 MB/s      96 B/op     7 allocs/op
~Hasher/hasher-sha1-5000B-16        	              96476	     12523 ns/op	 399.25 MB/s    5536 B/op     7 allocs/op
~Hasher/objecthash-sha1-5000B-16    	             105376	     10983 ns/op	 455.27 MB/s     272 B/op     9 allocs/op
~Hasher/objecthash-sha256-5000B-16  	             420741	      2828 ns/op	1767.77 MB/s      96 B/op     7 allocs/op
~HashFromHex/hasher-parse-sha1-valid-16         	23243548     64.65 ns/op	 618.69 MB/s      48 B/op     1 allocs/op
~HashFromHex/objecthash-fromhex-sha1-valid-16   	18120699     79.62 ns/op	 502.36 MB/s      72 B/op     2 allocs/op
~HashFromHex/objecthash-fromhex-sha256-valid-16 	 8969871    124.2 ns/op	     515.22 MB/s      96 B/op     2 allocs/op

Signed-off-by: Paulo Gomes <paulo.gomes@suse.com>
    @pjbgf
    pjbgf committed Nov 10, 2023
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