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[78.66.223.148]) by smtp.gmail.com with ESMTPSA id t20sm855663ljk.58.2020.12.20.23.55.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 20 Dec 2020 23:55:23 -0800 (PST) From: =?utf-8?q?Martin_=C3=85gren?= To: Ross Light Cc: git@vger.kernel.org Subject: [PATCH 1/2] pack-format.txt: define "varint" format Date: Mon, 21 Dec 2020 08:54:58 +0100 Message-Id: <42c6206b102cd97290fd9ad207bb39b20660064c.1608537234.git.martin.agren@gmail.com> X-Mailer: git-send-email 2.30.0.rc1 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org We define our varint format pretty much on the fly as we describe a pack file entry. In preparation for referring to it in more places in this document, define "varint" and refer to it. Signed-off-by: Martin Ågren --- Documentation/technical/pack-format.txt | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt index f96b2e605f..42198de74c 100644 --- a/Documentation/technical/pack-format.txt +++ b/Documentation/technical/pack-format.txt @@ -55,6 +55,15 @@ Valid object types are: Type 5 is reserved for future expansion. Type 0 is invalid. +=== Variable-length integer encoding + +This document uses "varint" 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. + === Deltified representation Conceptually there are only four object types: commit, tree, tag and @@ -196,10 +205,10 @@ Pack file entry: <+ 1-byte size extension bit (MSB) type (next 3 bit) size0 (lower 4-bit) - n-byte sizeN (as long as MSB is set, each 7-bit) - size0..sizeN form 4+7+7+..+7 bit integer, size0 - is the least significant part, and sizeN is the - most significant part. + n-byte size1 (varint encoding; present if MSB is set) + If the MSB is set, the size is size0 + 16*size1, otherwise + it is size0. (Equivalently, the entire packed object header + is a varint encoding of (size/16)*128 + type*16 + size%16.) packed object data: If it is not DELTA, then deflated bytes (the size above is the size before compression).