From 7b001bff4609b80ad626b429cc069b40a1d5fab3 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Sun, 14 May 2017 21:02:59 -0300 Subject: lzo.txt: standardize document format Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - Add markups for section titles; - mark literal blocks; - use ".. important::" for an important note. Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Jonathan Corbet --- Documentation/lzo.txt | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) (limited to 'Documentation/lzo.txt') diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt index 285c54f66779..6fa6a93d0949 100644 --- a/Documentation/lzo.txt +++ b/Documentation/lzo.txt @@ -1,8 +1,9 @@ - +=========================================================== LZO stream format as understood by Linux's LZO decompressor =========================================================== Introduction +============ This is not a specification. No specification seems to be publicly available for the LZO stream format. This document describes what input format the LZO @@ -14,12 +15,13 @@ Introduction for future bug reports. Description +=========== The stream is composed of a series of instructions, operands, and data. The instructions consist in a few bits representing an opcode, and bits forming the operands for the instruction, whose size and position depend on the opcode and on the number of literals copied by previous instruction. The - operands are used to indicate : + operands are used to indicate: - a distance when copying data from the dictionary (past output buffer) - a length (number of bytes to copy from dictionary) @@ -38,7 +40,7 @@ Description of bits in the operand. If the number of bits isn't enough to represent the length, up to 255 may be added in increments by consuming more bytes with a rate of at most 255 per extra byte (thus the compression ratio cannot exceed - around 255:1). The variable length encoding using #bits is always the same : + around 255:1). The variable length encoding using #bits is always the same:: length = byte & ((1 << #bits) - 1) if (!length) { @@ -67,15 +69,19 @@ Description instruction may encode this distance (0001HLLL), it takes one LE16 operand for the distance, thus requiring 3 bytes. - IMPORTANT NOTE : in the code some length checks are missing because certain - instructions are called under the assumption that a certain number of bytes - follow because it has already been guaranteed before parsing the instructions. - They just have to "refill" this credit if they consume extra bytes. This is - an implementation design choice independent on the algorithm or encoding. + .. important:: + + In the code some length checks are missing because certain instructions + are called under the assumption that a certain number of bytes follow + because it has already been guaranteed before parsing the instructions. + They just have to "refill" this credit if they consume extra bytes. This + is an implementation design choice independent on the algorithm or + encoding. Byte sequences +============== - First byte encoding : + First byte encoding:: 0..17 : follow regular instruction encoding, see below. It is worth noting that codes 16 and 17 will represent a block copy from @@ -91,7 +97,7 @@ Byte sequences state = 4 [ don't copy extra literals ] skip byte - Instruction encoding : + Instruction encoding:: 0 0 0 0 X X X X (0..15) Depends on the number of literals copied by the last instruction. @@ -156,6 +162,7 @@ Byte sequences distance = (H << 3) + D + 1 Authors +======= This document was written by Willy Tarreau on 2014/07/19 during an analysis of the decompression code available in Linux 3.16-rc5. The code is -- cgit v1.2.3-58-ga151