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[31.211.229.121]) by smtp.gmail.com with ESMTPSA id a1sm2670493lfb.10.2020.08.15.09.06.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 15 Aug 2020 09:06:28 -0700 (PDT) From: =?utf-8?q?Martin_=C3=85gren?= To: git@vger.kernel.org Cc: "brian m. carlson" , Derrick Stolee , Junio C Hamano Subject: [PATCH v2 2/4] index-format.txt: document SHA-256 index format Date: Sat, 15 Aug 2020 18:06:00 +0200 Message-Id: <14bd0d93620a917f5373ccef2867184ab7bb0811.1597506837.git.martin.agren@gmail.com> X-Mailer: git-send-email 2.28.0.297.g1956fa8f8d In-Reply-To: References: MIME-Version: 1.0 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org 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 --- Documentation/technical/index-format.txt | 34 +++++++++++++----------- 1 file changed, 18 insertions(+), 16 deletions(-) diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt index faa25c5c52..f9a3644711 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 @@ -32,8 +35,7 @@ Git index format Extension data - - 160-bit SHA-1 over the content of the index file before this - checksum. + - Hash checksum over the content of the index file before this checksum. == Index entry @@ -80,7 +82,7 @@ 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 + Object name for the represented object A 16-bit 'flags' field split into (high to low bits) @@ -160,8 +162,8 @@ Git index format - A newline (ASCII 10); and - - 160-bit object name for the object that would result from writing - this span of index as a tree. + - Object name for the object that would result from writing this span + of index as a tree. 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 @@ -198,7 +200,7 @@ Git index format stage 1 to 3 (a missing stage is represented by "0" in this field); 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). === Split index @@ -211,8 +213,8 @@ 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.. If all 160 bits are zero, the + - Hash of the shared index file. The shared index file path + is $GIT_DIR/sharedindex.. 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 +255,10 @@ 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 +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 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 +332,12 @@ 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" + + + Hash("TREE" + + "REUC" + ) == Index Entry Offset Table