[PATCH v2 0/3] bitmap-format.txt: fix some formatting issues and include checksum info

From: Abhradeep Chakraborty via GitGitGadget <gitgitgadget@gmail.com>
Date: Jun 7, 2022, 17:43 UTC
Message-ID: <pull.1246.v2.git.1654623814.gitgitgadget@gmail.com>
In-Reply-To: <pull.1246.git.1654177966.gitgitgadget@gmail.com>

There are some issues in the bitmap-format html page. For example, some nested lists are shown as top-level lists (e.g. [1]- Here BITMAP_OPT_FULL_DAG (0x1) and BITMAP_OPT_HASH_CACHE (0x4) are shown as top-level list). There is also a need of adding info about trailing checksum in the docs.

Changes since v1:

 * a new commit addressing bitmap-format.txt html page generation is added
 * Remove extra indentation from the previous change
 * elaborate more about the trailing checksum (as suggested by Kaartic)

initial version:

 * first commit fixes some formatting issues
 * information about trailing checksum in the bitmap file is added in the
   bitmap-format doc.

[1] https://git-scm.com/docs/bitmap-format#_on_disk_format

Abhradeep Chakraborty (3):
  bitmap-format.txt: feed the file to asciidoc to generate html
  bitmap-format.txt: fix some formatting issues
  bitmap-format.txt: add information for trailing checksum

 Documentation/Makefile                    |  1 +
 Documentation/technical/bitmap-format.txt | 24 +++++++++++------------
 2 files changed, 12 insertions(+), 13 deletions(-)

base-commit: 2668e3608e47494f2f10ef2b6e69f08a84816bcb
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1246%2FAbhra303%2Ffix-doc-formatting-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1246/Abhra303/fix-doc-formatting-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1246

Range-diff vs v1:

-: ----------- > 1: a1b9bd9af90 bitmap-format.txt: feed the file to asciidoc to generate html
1: 976361e624a ! 2: cb919513c14 bitmap-format.txt: fix some formatting issues
@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cac
-
The following flags are supported:
-
-- - BITMAP_OPT_FULL_DAG (0x1) REQUIRED
-- This flag must always be present. It implies that the
-- bitmap index has been generated for a packfile or
-- multi-pack index (MIDX) with full closure (i.e. where
-- every single object in the packfile/MIDX can find its
-- parent links inside the same packfile/MIDX). This is a
-- requirement for the bitmap index format, also present in
-- JGit, that greatly reduces the complexity of the
-- implementation.
+ - BITMAP_OPT_FULL_DAG (0x1) REQUIRED
+ This flag must always be present. It implies that the
+ bitmap index has been generated for a packfile or
+@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
+ requirement for the bitmap index format, also present in
+ JGit, that greatly reduces the complexity of the
+ implementation.
-
-- - BITMAP_OPT_HASH_CACHE (0x4)
-- If present, the end of the bitmap file contains
-- `N` 32-bit name-hash values, one per object in the
-- pack/MIDX. The format and meaning of the name-hash is
-- described below.
-+ - BITMAP_OPT_FULL_DAG (0x1) REQUIRED
-+ This flag must always be present. It implies that the
-+ bitmap index has been generated for a packfile or
-+ multi-pack index (MIDX) with full closure (i.e. where
-+ every single object in the packfile/MIDX can find its
-+ parent links inside the same packfile/MIDX). This is a
-+ requirement for the bitmap index format, also present in
-+ JGit, that greatly reduces the complexity of the
-+ implementation.
-+ - BITMAP_OPT_HASH_CACHE (0x4)
-+ If present, the end of the bitmap file contains
-+ `N` 32-bit name-hash values, one per object in the
-+ pack/MIDX. The format and meaning of the name-hash is
-+ described below.
+ - BITMAP_OPT_HASH_CACHE (0x4)
+ If present, the end of the bitmap file contains
+ `N` 32-bit name-hash values, one per object in the
+@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
+ described below.

4-byte entry count (network byte order)
-
@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cac
Each entry contains the following:

- - 4-byte object position (network byte order)
-- The position **in the index for the packfile or
-- multi-pack index** where the bitmap for this commit is
-- found.
--
++ ** 4-byte object position (network byte order)
+ The position **in the index for the packfile or
+ multi-pack index** where the bitmap for this commit is
+ found.
+
- - 1-byte XOR-offset
-- The xor offset used to compress this bitmap. For an entry
-- in position `x`, a XOR offset of `y` means that the actual
-- bitmap representing this commit is composed by XORing the
-- bitmap for this entry with the bitmap in entry `x-y` (i.e.
-- the bitmap `y` entries before this one).
--
-- Note that this compression can be recursive. In order to
-- XOR this entry with a previous one, the previous entry needs
-- to be decompressed first, and so on.
--
-- The hard-limit for this offset is 160 (an entry can only be
-- xor'ed against one of the 160 entries preceding it). This
-- number is always positive, and hence entries are always xor'ed
-- with **previous** bitmaps, not bitmaps that will come afterwards
-- in the index.
--
++ ** 1-byte XOR-offset
+ The xor offset used to compress this bitmap. For an entry
+ in position `x`, a XOR offset of `y` means that the actual
+ bitmap representing this commit is composed by XORing the
+@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.
+ with **previous** bitmaps, not bitmaps that will come afterwards
+ in the index.
+
- - 1-byte flags for this bitmap
-- At the moment the only available flag is `0x1`, which hints
-- that this bitmap can be re-used when rebuilding bitmap indexes
-- for the repository.
--
++ ** 1-byte flags for this bitmap
+ At the moment the only available flag is `0x1`, which hints
+ that this bitmap can be re-used when rebuilding bitmap indexes
+ for the repository.
+
- - The compressed bitmap itself, see Appendix A.
-+ ** 4-byte object position (network byte order)
-+ The position **in the index for the packfile or
-+ multi-pack index** where the bitmap for this commit is
-+ found.
-+
-+ ** 1-byte XOR-offset
-+ The xor offset used to compress this bitmap. For an entry
-+ in position `x`, a XOR offset of `y` means that the actual
-+ bitmap representing this commit is composed by XORing the
-+ bitmap for this entry with the bitmap in entry `x-y` (i.e.
-+ the bitmap `y` entries before this one).
-+
-+ Note that this compression can be recursive. In order to
-+ XOR this entry with a previous one, the previous entry needs
-+ to be decompressed first, and so on.
-+
-+ The hard-limit for this offset is 160 (an entry can only be
-+ xor'ed against one of the 160 entries preceding it). This
-+ number is always positive, and hence entries are always xor'ed
-+ with **previous** bitmaps, not bitmaps that will come afterwards
-+ in the index.
-+
-+ ** 1-byte flags for this bitmap
-+ At the moment the only available flag is `0x1`, which hints
-+ that this bitmap can be re-used when rebuilding bitmap indexes
-+ for the repository.
-+
-+ ** The compressed bitmap itself, see Appendix A.
++ ** The compressed bitmap itself, see Appendix A.

== Appendix A: Serialization format for an EWAH bitmap

2: ba534b5d486 ! 3: 2171d31fb2b bitmap-format.txt: add information for trailing checksum
@@ Commit message
## Documentation/technical/bitmap-format.txt ##
@@ Documentation/technical/bitmap-format.txt: MIDXs, both the bit-cache and rev-cache extensions are required.

- ** The compressed bitmap itself, see Appendix A.
+ ** The compressed bitmap itself, see Appendix A.

+ * TRAILER:
+
-+ Index checksum of the above contents.
++ Index checksum of the above contents. It is a 20-byte SHA1 checksum.
+
== Appendix A: Serialization format for an EWAH bitmap

-- 
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