diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/dontdiff | 1 | ||||
| -rw-r--r-- | Documentation/lzo.txt | 39 | ||||
| -rw-r--r-- | Documentation/process/4.Coding.rst | 2 | ||||
| -rw-r--r-- | Documentation/translations/it_IT/process/4.Coding.rst | 2 |
4 files changed, 34 insertions, 10 deletions
diff --git a/Documentation/dontdiff b/Documentation/dontdiff index 2228fcc8e29f..ef25a066d952 100644 --- a/Documentation/dontdiff +++ b/Documentation/dontdiff @@ -106,7 +106,6 @@ compile.h* conf config config-* -config_data.h* config.mak config.mak.autogen conmakehash diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt index 6fa6a93d0949..f79934225d8d 100644 --- a/Documentation/lzo.txt +++ b/Documentation/lzo.txt @@ -78,16 +78,34 @@ Description is an implementation design choice independent on the algorithm or encoding. +Versions + +0: Original version +1: LZO-RLE + +Version 1 of LZO implements an extension to encode runs of zeros using run +length encoding. This improves speed for data with many zeros, which is a +common case for zram. This modifies the bitstream in a backwards compatible way +(v1 can correctly decompress v0 compressed data, but v0 cannot read v1 data). + +For maximum compatibility, both versions are available under different names +(lzo and lzo-rle). Differences in the encoding are noted in this document with +e.g.: version 1 only. + Byte sequences ============== 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 - the dictionary which is empty, and that they will always be + 0..16 : follow regular instruction encoding, see below. It is worth + noting that code 16 will represent a block copy from the + dictionary which is empty, and that it will always be invalid at this place. + 17 : bitstream version. If the first byte is 17, the next byte + gives the bitstream version (version 1 only). If the first byte + is not 17, the bitstream version is 0. + 18..21 : copy 0..3 literals state = (byte - 17) = 0..3 [ copy <state> literals ] skip byte @@ -140,6 +158,11 @@ Byte sequences state = S (copy S literals after this block) End of stream is reached if distance == 16384 + In version 1 only, this instruction is also used to encode a run of + zeros if distance = 0xbfff, i.e. H = 1 and the D bits are all 1. + In this case, it is followed by a fourth byte, X. + run length = ((X << 3) | (0 0 0 0 0 L L L)) + 4. + 0 0 1 L L L L L (32..63) Copy of small block within 16kB distance (preferably less than 34B) length = 2 + (L ?: 31 + (zero_bytes * 255) + non_zero_byte) @@ -165,7 +188,9 @@ 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 - tricky, it is possible that this document contains mistakes or that a few - corner cases were overlooked. In any case, please report any doubt, fix, or - proposed updates to the author(s) so that the document can be updated. + analysis of the decompression code available in Linux 3.16-rc5, and updated + by Dave Rodgman <dave.rodgman@arm.com> on 2018/10/30 to introduce run-length + encoding. The code is tricky, it is possible that this document contains + mistakes or that a few corner cases were overlooked. In any case, please + report any doubt, fix, or proposed updates to the author(s) so that the + document can be updated. diff --git a/Documentation/process/4.Coding.rst b/Documentation/process/4.Coding.rst index cfe264889447..4b7a5ab3cec1 100644 --- a/Documentation/process/4.Coding.rst +++ b/Documentation/process/4.Coding.rst @@ -249,7 +249,7 @@ features; most of these are found in the "kernel hacking" submenu. Several of these options should be turned on for any kernel used for development or testing purposes. In particular, you should turn on: - - ENABLE_WARN_DEPRECATED, ENABLE_MUST_CHECK, and FRAME_WARN to get an + - ENABLE_MUST_CHECK and FRAME_WARN to get an extra set of warnings for problems like the use of deprecated interfaces or ignoring an important return value from a function. The output generated by these warnings can be verbose, but one need not worry about diff --git a/Documentation/translations/it_IT/process/4.Coding.rst b/Documentation/translations/it_IT/process/4.Coding.rst index c61059015e52..c05b89e616dd 100644 --- a/Documentation/translations/it_IT/process/4.Coding.rst +++ b/Documentation/translations/it_IT/process/4.Coding.rst @@ -264,7 +264,7 @@ La maggior parte di queste opzioni possono essere attivate per qualsiasi kernel utilizzato per lo sviluppo o a scopo di test. In particolare dovreste attivare: - - ENABLE_WARN_DEPRECATED, ENABLE_MUST_CHECK, e FRAME_WARN per ottenere degli + - ENABLE_MUST_CHECK e FRAME_WARN per ottenere degli avvertimenti dedicati a problemi come l'uso di interfacce deprecate o l'ignorare un importante valore di ritorno di una funzione. Il risultato generato da questi avvertimenti può risultare verboso, ma non bisogna |