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authorDave Rodgman <dave.rodgman@arm.com>2019-03-08 03:30:44 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-03-08 05:32:03 +0300
commit45ec975efb527625629d123f30597673889f52ca (patch)
tree38ea802c92b6430e1fdc8686589fcad3d85e740a /Documentation/lzo.txt
parent5ee4014af99f77dac89e01961b717d13ff1a8ea5 (diff)
downloadlinux-45ec975efb527625629d123f30597673889f52ca.tar.xz
lib/lzo: separate lzo-rle from lzo
To prevent any issues with persistent data, separate lzo-rle from lzo so that it is treated as a separate algorithm, and lzo is still available. Link: http://lkml.kernel.org/r/20190205155944.16007-3-dave.rodgman@arm.com Signed-off-by: Dave Rodgman <dave.rodgman@arm.com> Cc: David S. Miller <davem@davemloft.net> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Markus F.X.J. Oberhumer <markus@oberhumer.com> Cc: Matt Sealey <matt.sealey@arm.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <nitingupta910@gmail.com> Cc: Richard Purdie <rpurdie@openedhand.com> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: Sonny Rao <sonnyrao@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/lzo.txt')
-rw-r--r--Documentation/lzo.txt12
1 files changed, 8 insertions, 4 deletions
diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt
index 306c60344ca7..f79934225d8d 100644
--- a/Documentation/lzo.txt
+++ b/Documentation/lzo.txt
@@ -88,6 +88,10 @@ 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
==============
@@ -99,8 +103,8 @@ Byte sequences
invalid at this place.
17 : bitstream version. If the first byte is 17, the next byte
- gives the bitstream version. If the first byte is not 17,
- the bitstream version is 0.
+ 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 ]
@@ -154,8 +158,8 @@ Byte sequences
state = S (copy S literals after this block)
End of stream is reached if distance == 16384
- In version 1, 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 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.