Merge branch 'ac/bitmap-format-doc' into maint

Adjust technical/bitmap-format to be formatted by AsciiDoc, and
add some missing information to the documentation.
source: <pull.1246.v4.git.1655355834.gitgitgadget@gmail.com>

* ac/bitmap-format-doc:
  bitmap-format.txt: add information for trailing checksum
  bitmap-format.txt: fix some formatting issues
  bitmap-format.txt: feed the file to asciidoc to generate html

Documentation/Makefile

@@ -94,6 +94,7 @@ TECH_DOCS += MyFirstContribution
 TECH_DOCS += MyFirstObjectWalk
 TECH_DOCS += SubmittingPatches
 TECH_DOCS += ToolsForGit
+TECH_DOCS += technical/bitmap-format
 TECH_DOCS += technical/bundle-format
 TECH_DOCS += technical/cruft-packs
 TECH_DOCS += technical/hash-function-transition

Documentation/technical/bitmap-format.txt

@@ -25,9 +25,9 @@ An object is uniquely described by its bit position within a bitmap:
 	is defined as follows:
 
 		o1 <= o2 <==> pack(o1) <= pack(o2) /\ offset(o1) <= offset(o2)
-
-	The ordering between packs is done according to the MIDX's .rev file.
-	Notably, the preferred pack sorts ahead of all other packs.
++
+The ordering between packs is done according to the MIDX's .rev file.
+Notably, the preferred pack sorts ahead of all other packs.
 
 The on-disk representation (described below) of a bitmap is the same regardless
 of whether or not that bitmap belongs to a packfile or a MIDX. The only
@@ -39,19 +39,22 @@ MIDXs, both the bit-cache and rev-cache extensions are required.
 
 == On-disk format
 
-	- A header appears at the beginning:
+    * A header appears at the beginning:
 
-		4-byte signature: {'B', 'I', 'T', 'M'}
+	4-byte signature: :: {'B', 'I', 'T', 'M'}
+
+	2-byte version number (network byte order): ::
 
-		2-byte version number (network byte order)
 	    The current implementation only supports version 1
 	    of the bitmap index (the same one as JGit).
 
-		2-byte flags (network byte order)
+	2-byte flags (network byte order): ::
 
 	    The following flags are supported:
 
-			- BITMAP_OPT_FULL_DAG (0x1) REQUIRED
+	    ** {empty}
+	    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
@@ -61,75 +64,83 @@ MIDXs, both the bit-cache and rev-cache extensions are required.
 	    JGit, that greatly reduces the complexity of the
 	    implementation.
 
-			- BITMAP_OPT_HASH_CACHE (0x4)
+	    ** {empty}
+	    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.
 
-		4-byte entry count (network byte order)
-
+	4-byte entry count (network byte order): ::
 	    The total count of entries (bitmapped commits) in this bitmap index.
 
-		20-byte checksum
-
+	20-byte checksum: ::
 	    The SHA1 checksum of the pack/MIDX this bitmap index
 	    belongs to.
 
-	- 4 EWAH bitmaps that act as type indexes
-
-		Type indexes are serialized after the hash cache in the shape
-		of four EWAH bitmaps stored consecutively (see Appendix A for
-		the serialization format of an EWAH bitmap).
-
-		There is a bitmap for each Git object type, stored in the following
-		order:
-
+    * 4 EWAH bitmaps that act as type indexes
++
+Type indexes are serialized after the hash cache in the shape
+of four EWAH bitmaps stored consecutively (see Appendix A for
+the serialization format of an EWAH bitmap).
++
+There is a bitmap for each Git object type, stored in the following
+order:
++
     - Commits
     - Trees
     - Blobs
     - Tags
 
-		In each bitmap, the `n`th bit is set to true if the `n`th object
-		in the packfile or multi-pack index is of that type.
++
+In each bitmap, the `n`th bit is set to true if the `n`th object
+in the packfile or multi-pack index is of that type.
++
+The obvious consequence is that the OR of all 4 bitmaps will result
+in a full set (all bits set), and the AND of all 4 bitmaps will
+result in an empty bitmap (no bits set).
 
-		The obvious consequence is that the OR of all 4 bitmaps will result
-		in a full set (all bits set), and the AND of all 4 bitmaps will
-		result in an empty bitmap (no bits set).
+    * N entries with compressed bitmaps, one for each indexed commit
++
+Where `N` is the total amount of entries in this bitmap index.
+Each entry contains the following:
 
-	- N entries with compressed bitmaps, one for each indexed commit
-
-		Where `N` is the total amount of entries in this bitmap index.
-		Each entry contains the following:
-
-		- 4-byte object position (network byte order)
+	** {empty}
+	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
+	** {empty}
+	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: 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.
 
-			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
+	** {empty}
+	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.
+
+	* {empty}
+	TRAILER: ::
+		Trailing checksum of the preceding contents.
 
 == Appendix A: Serialization format for an EWAH bitmap
 
@@ -142,8 +153,8 @@ implementation:
 	- 4-byte number of words of the COMPRESSED bitmap, when stored
 
 	- N x 8-byte words, as specified by the previous field
-
-		This is the actual content of the compressed bitmap.
++
+This is the actual content of the compressed bitmap.
 
 	- 4-byte position of the current RLW for the compressed
 		bitmap