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From: Derrick Stolee <stolee@gmail.com>
To: "Martin Ågren" <martin.agren@gmail.com>,
	"brian m. carlson" <sandals@crustytoothpaste.net>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 2/5] index-format.txt: document SHA-256 index format
Date: Fri, 14 Aug 2020 08:28:13 -0400	[thread overview]
Message-ID: <e9963ef1-cecd-cdf8-a5cf-2be884d8ced6@gmail.com> (raw)
In-Reply-To: <e811455d55cdb222a85d880f3cf3d5e28a8d4c91.1597406877.git.martin.agren@gmail.com>

On 8/14/2020 8:21 AM, Martin Ågren wrote:
> Similar to a recent commit, 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.
> 
> Signed-off-by: Martin Ågren <martin.agren@gmail.com>
> ---
>  Documentation/technical/index-format.txt | 27 +++++++++++++-----------
>  1 file changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt
> index faa25c5c52..827ece2ed1 100644
> --- a/Documentation/technical/index-format.txt
> +++ b/Documentation/technical/index-format.txt
> @@ -3,8 +3,11 @@ Git index format
>  
>  == The Git index file has the following format
>  
> -  All binary numbers are in network byte order. Version 2 is described
> -  here unless stated otherwise.
> +  All binary numbers are in network byte order.
> +  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
>  
> @@ -32,7 +35,7 @@ Git index format
>  
>       Extension data
>  
> -   - 160-bit SHA-1 over the content of the index file before this
> +   - 160-bit hash checksum over the content of the index file before this
>       checksum.

If this hash is flexible, then "160-bit" is not correct anymore, right?

>  == Index entry
> @@ -80,7 +83,7 @@ Git index format
>    32-bit file size
>      This is the on-disk size from stat(2), truncated to 32-bit.
>  
> -  160-bit SHA-1 for the represented object
> +  160-bit object name for the represented object

Same here. The later instances of "160-bit" were dropped.

>    A 16-bit 'flags' field split into (high to low bits)
>  
> @@ -211,8 +214,8 @@ Git index format
>  
>    The extension consists of:
>  
> -  - 160-bit SHA-1 of the shared index file. The shared index file path
> -    is $GIT_DIR/sharedindex.<SHA-1>. If all 160 bits are zero, the
> +  - Hash of the shared index file. The shared index file path
> +    is $GIT_DIR/sharedindex.<hash>. If all bits are zero, the
>      index does not require a shared index file.
>  
>    - An ewah-encoded delete bitmap, each bit represents an entry in the
> @@ -253,10 +256,10 @@ Git index format
>  
>    - 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.
>  
> -  - 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.
>  
>    - NUL-terminated string of per-dir exclude file name. This usually
> @@ -285,13 +288,13 @@ The remaining data of each directory block is grouped by type:
>    - An ewah bitmap, the n-th bit records "check-only" bit of
>      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.
>  
>    - An array of stat data. The n-th data corresponds with the n-th
>      "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.
>  
>    - One NUL.
> @@ -330,12 +333,12 @@ The remaining data of each directory block is grouped by type:
>  
>    - 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
>  	long, "REUC" extension that is M-bytes long, followed by "EOIE",
>  	then the hash would be:
>  
> -	SHA-1("TREE" + <binary representation of N> +
> +	Hash("TREE" + <binary representation of N> +
>  		"REUC" + <binary representation of M>)
>  
>  == Index Entry Offset Table
> 

Thanks,
-Stolee



  reply	other threads:[~2020-08-14 12:28 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-13 22:48 [PATCH 0/2] Documentation updates for SHA-256 brian m. carlson
2020-08-13 22:49 ` [PATCH 1/2] docs: document SHA-256 pack and indices brian m. carlson
2020-08-14  2:26   ` Derrick Stolee
2020-08-13 22:49 ` [PATCH 2/2] docs: fix step in transition plan brian m. carlson
2020-08-14 12:21   ` Martin Ågren
2020-08-14  2:33 ` [PATCH 0/2] Documentation updates for SHA-256 Derrick Stolee
2020-08-14  4:47   ` Junio C Hamano
2020-08-14 20:20     ` brian m. carlson
2020-08-14 20:25       ` Junio C Hamano
2020-08-14 12:21 ` [PATCH 0/5] more SHA-256 documentation Martin Ågren
2020-08-14 12:21   ` [PATCH 1/5] http-protocol.txt: document SHA-256 "want"/"have" format Martin Ågren
2020-08-14 17:28     ` Junio C Hamano
2020-08-14 20:23       ` brian m. carlson
2020-08-14 20:32         ` Martin Ågren
2020-08-14 20:39         ` Junio C Hamano
2020-08-14 20:47           ` Junio C Hamano
2020-08-14 12:21   ` [PATCH 2/5] index-format.txt: document SHA-256 index format Martin Ågren
2020-08-14 12:28     ` Derrick Stolee [this message]
2020-08-14 14:05       ` Martin Ågren
2020-08-14 12:21   ` [PATCH 3/5] protocol-capabilities.txt: clarify "allow-x-sha1-in-want" re SHA-256 Martin Ågren
2020-08-14 12:31     ` Derrick Stolee
2020-08-14 14:05       ` Martin Ågren
2020-08-14 17:33     ` Junio C Hamano
2020-08-14 20:35       ` Martin Ågren
2020-08-14 20:43         ` Junio C Hamano
2020-08-14 12:21   ` [PATCH 4/5] shallow.txt: document SHA-256 shallow format Martin Ågren
2020-08-14 12:21   ` [PATCH 5/5] commit-graph-format.txt: fix "Hash Version" description Martin Ågren
2020-08-14 12:37     ` Derrick Stolee
2020-08-14 14:10       ` Martin Ågren
2020-08-14 20:28   ` [PATCH 0/5] more SHA-256 documentation brian m. carlson
2020-08-15 16:05   ` [PATCH v2 0/4] " Martin Ågren
2020-08-15 16:05     ` [PATCH v2 1/4] http-protocol.txt: document SHA-256 "want"/"have" format Martin Ågren
2020-08-15 16:06     ` [PATCH v2 2/4] index-format.txt: document SHA-256 index format Martin Ågren
2020-08-15 16:06     ` [PATCH v2 3/4] protocol-capabilities.txt: clarify "allow-x-sha1-in-want" re SHA-256 Martin Ågren
2020-08-15 16:06     ` [PATCH v2 4/4] shallow.txt: document SHA-256 shallow format Martin Ågren

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