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index-format.txt: document SHA-256 index format

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Document that in SHA-1 repositories, we use SHA-1 and in SHA-256
repositories, we use SHA-256, then replace all other uses of "SHA-1"
with something more neutral. Avoid referring to "160-bit" hash values.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Martin Ågren 2020-08-15 18:06:00 +02:00 committed by Junio C Hamano
parent 5b6422a616
commit 123712ba41
1 changed files with 18 additions and 16 deletions
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34
Documentation/technical/index-format.txt
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@ -3,8 +3,11 @@ Git index format
== The Git index file has the following format == The Git index file has the following format
All binary numbers are in network byte order. Version 2 is described All binary numbers are in network byte order.
here unless stated otherwise. In a repository using the traditional SHA-1, checksums and object IDs
(object names) mentioned below are all computed using SHA-1. Similarly,
in SHA-256 repositories, these values are computed using SHA-256.
Version 2 is described here unless stated otherwise.
- A 12-byte header consisting of - A 12-byte header consisting of
@ -32,8 +35,7 @@ Git index format
Extension data Extension data
- 160-bit SHA-1 over the content of the index file before this - Hash checksum over the content of the index file before this checksum.
checksum.
== Index entry == Index entry
@ -80,7 +82,7 @@ Git index format
32-bit file size 32-bit file size
This is the on-disk size from stat(2), truncated to 32-bit. This is the on-disk size from stat(2), truncated to 32-bit.
160-bit SHA-1 for the represented object Object name for the represented object
A 16-bit 'flags' field split into (high to low bits) A 16-bit 'flags' field split into (high to low bits)
@ -160,8 +162,8 @@ Git index format
- A newline (ASCII 10); and - A newline (ASCII 10); and
- 160-bit object name for the object that would result from writing - Object name for the object that would result from writing this span
this span of index as a tree. of index as a tree.
An entry can be in an invalidated state and is represented by having An entry can be in an invalidated state and is represented by having
a negative number in the entry_count field. In this case, there is no a negative number in the entry_count field. In this case, there is no
@ -198,7 +200,7 @@ Git index format
stage 1 to 3 (a missing stage is represented by "0" in this field); stage 1 to 3 (a missing stage is represented by "0" in this field);
and and
- At most three 160-bit object names of the entry in stages from 1 to 3 - At most three object names of the entry in stages from 1 to 3
(nothing is written for a missing stage). (nothing is written for a missing stage).
=== Split index === Split index
@ -211,8 +213,8 @@ Git index format
The extension consists of: The extension consists of:
- 160-bit SHA-1 of the shared index file. The shared index file path - Hash of the shared index file. The shared index file path
is $GIT_DIR/sharedindex.<SHA-1>. If all 160 bits are zero, the is $GIT_DIR/sharedindex.<hash>. If all bits are zero, the
index does not require a shared index file. index does not require a shared index file.
- An ewah-encoded delete bitmap, each bit represents an entry in the - An ewah-encoded delete bitmap, each bit represents an entry in the
@ -253,10 +255,10 @@ Git index format
- 32-bit dir_flags (see struct dir_struct) - 32-bit dir_flags (see struct dir_struct)
- 160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file - Hash of $GIT_DIR/info/exclude. A null hash means the file
does not exist. does not exist.
- 160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does - Hash of core.excludesfile. A null hash means the file does
not exist. not exist.
- NUL-terminated string of per-dir exclude file name. This usually - NUL-terminated string of per-dir exclude file name. This usually
@ -285,13 +287,13 @@ The remaining data of each directory block is grouped by type:
- An ewah bitmap, the n-th bit records "check-only" bit of - An ewah bitmap, the n-th bit records "check-only" bit of
read_directory_recursive() for the n-th directory. read_directory_recursive() for the n-th directory.
- An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data - An ewah bitmap, the n-th bit indicates whether hash and stat data
is valid for the n-th directory and exists in the next data. is valid for the n-th directory and exists in the next data.
- An array of stat data. The n-th data corresponds with the n-th - An array of stat data. The n-th data corresponds with the n-th
"one" bit in the previous ewah bitmap. "one" bit in the previous ewah bitmap.
- An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit - An array of hashes. The n-th hash corresponds with the n-th "one" bit
in the previous ewah bitmap. in the previous ewah bitmap.
- One NUL. - One NUL.
@ -330,12 +332,12 @@ The remaining data of each directory block is grouped by type:
- 32-bit offset to the end of the index entries - 32-bit offset to the end of the index entries
- 160-bit SHA-1 over the extension types and their sizes (but not - Hash over the extension types and their sizes (but not
their contents). E.g. if we have "TREE" extension that is N-bytes their contents). E.g. if we have "TREE" extension that is N-bytes
long, "REUC" extension that is M-bytes long, followed by "EOIE", long, "REUC" extension that is M-bytes long, followed by "EOIE",
then the hash would be: then the hash would be:
SHA-1("TREE" + <binary representation of N> + Hash("TREE" + <binary representation of N> +
"REUC" + <binary representation of M>) "REUC" + <binary representation of M>)
== Index Entry Offset Table == Index Entry Offset Table