When the match is very long and found quickly, we can do
matchLength * nbCompares iterations through the chain
swapping, which can really slow down compression.
It is important to continue to look backwards if the current pattern
reaches `lowPrefixPtr`. If the pattern detection doesn't go all the
way to the beginning of the pattern, or the end of the pattern it
slows down the search instead of speeding it up.
The slow unit in `round_trip_stream_fuzzer` used to take 12 seconds
to run with -O3, now it takes 0.2 seconds.
Credit to OSS-Fuzz
This diff fixes an issue in which we failed to clear the `dictCtx` in HC
compression. The `dictCtx` is not supposed to be used when an `extDict` is
present: matches found in the `dictCtx` do not account for the presence of an
`extDict` segment, and their offsets are therefore miscalculated when one is
present. This can lead to data corruption.
This diff clears the `dictCtx` whenever setting an `extDict`.
This issue was uncovered by @terrelln's fuzzing work.
It's now possible to select a custom LZ4_DISTANCE_MAX at compile time,
provided it's <= 65535.
However, in some cases (when compressing in byU16 mode),
the new distance wasn't respected,
as it used to implied that it was necessarily within range.
Added a distance check for this case.
Also : added a new TravisCI test which ensures that
custom LZ4_DISTANCE_MAX compiles correctly
and compresses correctly (relying on `assert()` to find outsized offsets).
When I did FAST_DEC_LOOP performance test, I found the
offset check is much more than v1.8.3
You will see the condition check difference via lzbench with dickens test case.
v1.8.3 34959
v.1.9.x 1055885
After investigate the code, we could see the difference.
v.1.8.3 SKIP the condition check if
if condition is true in:
https://github.com/lz4/lz4/blob/v1.8.3/lib/lz4.c#L1463
AND below condition is true
https://github.com/lz4/lz4/blob/v1.8.3/lib/lz4.c#L1478\
The offset check should be invoked.
v1.9.3
The offset check code will be invoked in every loop which lead to downgrade.
So the fix would be move this check to specific condition
to avoid useless condition check.
After this change, the call number is same as v1.8.3
Use the list of prerequisites instead of listing those files manually,
this way they will never fall out of sync.
Also update the amalgamation example to use a single cat command.
Fixes: a7e8d394 ("[amalgamation] add test")
Fixes: b192c86b ("[amalgamation] lz4frame.c")
Moved a few other tests to Makefiles.inc. Other things might need to go there.
Made a test for symlink appropriateness. Windows can NOT handle them the same way Unix-like operating systems do (if at all). This is mostly the same as the Visual C projects.
embed version info into .dll and .exes that are redistributed.
