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authorLinus Torvalds <torvalds@linux-foundation.org>2017-07-15 22:58:58 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-15 22:58:58 +0300
commit486088bc4689f826b80aa317b45ac9e42e8b25ee (patch)
treeadf5847a6119d24da990d9e336f005c4a316e6be /Documentation/lzo.txt
parent52f6c588c77b76d548201470c2a28263a41b462b (diff)
parent43e5f7e1fa66531777c49791014c3124ea9208d8 (diff)
downloadlinux-486088bc4689f826b80aa317b45ac9e42e8b25ee.tar.xz
Merge tag 'standardize-docs' of git://git.lwn.net/linux
Pull documentation format standardization from Jonathan Corbet: "This series converts a number of top-level documents to the RST format without incorporating them into the Sphinx tree. The hope is to bring some uniformity to kernel documentation and, perhaps more importantly, have our existing docs serve as an example of the desired formatting for those that will be added later. Mauro has gone through and fixed up a lot of top-level documentation files to make them conform to the RST format, but without moving or renaming them in any way. This will help when we incorporate the ones we want to keep into the Sphinx doctree, but the real purpose is to bring a bit of uniformity to our documentation and let the top-level docs serve as examples for those writing new ones" * tag 'standardize-docs' of git://git.lwn.net/linux: (84 commits) docs: kprobes.txt: Fix whitespacing tee.txt: standardize document format cgroup-v2.txt: standardize document format dell_rbu.txt: standardize document format zorro.txt: standardize document format xz.txt: standardize document format xillybus.txt: standardize document format vfio.txt: standardize document format vfio-mediated-device.txt: standardize document format unaligned-memory-access.txt: standardize document format this_cpu_ops.txt: standardize document format svga.txt: standardize document format static-keys.txt: standardize document format smsc_ece1099.txt: standardize document format SM501.txt: standardize document format siphash.txt: standardize document format sgi-ioc4.txt: standardize document format SAK.txt: standardize document format rpmsg.txt: standardize document format robust-futexes.txt: standardize document format ...
Diffstat (limited to 'Documentation/lzo.txt')
-rw-r--r--Documentation/lzo.txt27
1 files changed, 17 insertions, 10 deletions
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 <w@1wt.eu> on 2014/07/19 during an
analysis of the decompression code available in Linux 3.16-rc5. The code is