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Calascibetta Romain 2025-01-13 17:51:43 +01:00
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articles/2025-01-07-carton-and-cachet.md
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@ -28,8 +28,9 @@ Furthermore, if we have 2 blobs (2 versions of a file), one of which contains
'A' and the other contains 'A+B', the second blob will probably be saved in the 'A' and the other contains 'A+B', the second blob will probably be saved in the
form of a patch requiring the contents of the first blob and adding '+B'. At a form of a patch requiring the contents of the first blob and adding '+B'. At a
higher level and according to our use of Git, we understand that this second higher level and according to our use of Git, we understand that this second
level of compression is very interesting: we generally just add/remove new level of compression is very interesting: we generally just add/remove few lines
keywords in our files of our project. (like introduce a new function) or delete some (removing code) in our files of
our project.
However, there is a bias in what Git does and what we perceive. We often think However, there is a bias in what Git does and what we perceive. We often think
that when it comes to patching in the case of Git, we think of the that when it comes to patching in the case of Git, we think of the
@ -39,14 +40,14 @@ been added or deleted between two files, they are not necessarily optimal for
producing a _small_ patch. producing a _small_ patch.
In reality, what interests us in the case of the storage and transmission of In reality, what interests us in the case of the storage and transmission of
these patches over the network is not a form of lisibility in these patches but these patches over the network is not a form of readability in these patches but
an optimality in what can be considered as common between two files and what is an optimality in what can be considered as common between two files and what is
not. It is at this stage that the use of [duff][duff] is introduced. not. It is at this stage that the use of [duff][duff] is introduced.
This is a small library which can generate a patch between two files according This is a small library which can generate a patch between two files according
to the series of bytes common to both files. We're talking about 'series of to the series of bytes common to both files. We're talking about 'series of
bytes' here because these elements common to our two files are not necessary bytes' here because these elements common to our two files are not necessary
humanly readable. To find these series of common bytes, we use [Rabin's human readable. To find these series of common bytes, we use [Rabin's
fingerprint][rabin] algorithm: [a rolling hash][rolling-hash] used since time fingerprint][rabin] algorithm: [a rolling hash][rolling-hash] used since time
immemorial. immemorial.
@ -110,7 +111,7 @@ using a method (such as compression). Isomorphism ensures that we can 'undo'
this method and obtain exactly the same result again: this method and obtain exactly the same result again:
``` ```
x == decode(encode(x)) decode(encode(x)) == x
``` ```
This property is very important for emails because signatures exist in your This property is very important for emails because signatures exist in your
@ -392,8 +393,8 @@ to move a little faster, especially in terms of serializing our emails. Our
experience with ocaml-git also enabled us to identify the benefits of the PACK experience with ocaml-git also enabled us to identify the benefits of the PACK
file for emails. file for emails.
But the development of Miou was particularly helpful in satisfying us in terms But the development of [Miou][miou] was particularly helpful in satisfying us in
of program execution time, thanks to the ability to parallelize certain terms of program execution time, thanks to the ability to parallelize certain
calculations quite easily. calculations quite easily.
The format is still a little rough and not quite ready for the development of a The format is still a little rough and not quite ready for the development of a
@ -419,3 +420,4 @@ So, if you like what we're doing and want to help, you can make a donation via
[mbox]: https://en.wikipedia.org/wiki/Mbox [mbox]: https://en.wikipedia.org/wiki/Mbox
[donate-github]: https://github.com/sponsors/robur-coop [donate-github]: https://github.com/sponsors/robur-coop
[donate-iban]: https://robur.coop/Donate [donate-iban]: https://robur.coop/Donate
[miou]: https://github.com/robur-coop/miou