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[78.66.223.148]) by smtp.gmail.com with ESMTPSA id o6sm7019341ljc.124.2020.12.29.14.43.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Dec 2020 14:43:58 -0800 (PST) From: =?utf-8?q?Martin_=C3=85gren?= To: git@vger.kernel.org Cc: Ross Light , Junio C Hamano Subject: [PATCH v2] pack-format.txt: document sizes at start of delta data Date: Tue, 29 Dec 2020 23:43:35 +0100 Message-Id: <20201229224335.8989-1-martin.agren@gmail.com> X-Mailer: git-send-email 2.30.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org We document the delta data as a set of instructions, but forget to document the two sizes that precede those instructions: the size of the base object and the size of the object to be reconstructed. Fix this omission. Rather than cramming all the details about the encoding into the running text, introduce a separate section detailing our "size encoding" and refer to it. Reported-by: Ross Light Signed-off-by: Martin Ågren --- v1: https://lore.kernel.org/git/cover.1608537234.git.martin.agren@gmail.com/ Documentation/technical/pack-format.txt | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt index f96b2e605f..96d2fc589f 100644 --- a/Documentation/technical/pack-format.txt +++ b/Documentation/technical/pack-format.txt @@ -55,6 +55,18 @@ Valid object types are: Type 5 is reserved for future expansion. Type 0 is invalid. +=== Size encoding + +This document uses the following "size encoding" of non-negative +integers: From each byte, the seven least significant bits are +used to form the resulting integer. As long as the most significant +bit is 1, this process continues; the byte with MSB 0 provides the +last seven bits. The seven-bit chunks are concatenated. Later +values are more significant. + +This size encoding should not be confused with the "offset encoding", +which is also used in this document. + === Deltified representation Conceptually there are only four object types: commit, tree, tag and @@ -73,7 +85,10 @@ Ref-delta can also refer to an object outside the pack (i.e. the so-called "thin pack"). When stored on disk however, the pack should be self contained to avoid cyclic dependency. -The delta data is a sequence of instructions to reconstruct an object +The delta data starts with the size of the base object and the +size of the object to be reconstructed. These sizes are +encoded using the size encoding from above. The remainder of +the delta data is a sequence of instructions to reconstruct the object from the base object. If the base object is deltified, it must be converted to canonical form first. Each instruction appends more and more data to the target object until it's complete. There are two