* Intial commit to address 3090. Added support to decompress empty block
* Update zstd_decompress_block.c
Addressed review comments for the case of 'set_basic'
* Update lib/decompress/zstd_decompress_block.c
Co-authored-by: Nick Terrell <nickrterrell@gmail.com>
* Update lib/decompress/zstd_decompress_block.c
Co-authored-by: Nick Terrell <nickrterrell@gmail.com>
Co-authored-by: Nick Terrell <nickrterrell@gmail.com>
* first attempt at fast DMS short cache
* significant wins for some scenarios
* fix all clang regressions
* nits
* fix 1.5% gcc11 regression on hot 110Kdict scenario
* fix CI
* nit
* Add tags to doublefast hash table
* use tags in doublefast DMS
* Fix CI
* Clean up some hardcoded logic / constants
* Switch forCCtx to an enum
* nit
* add short cache to ip+1 long search
* Move tag size into hashLog
* Minor nits
* Truncate dictionaries greater than 16MB in short cache mode
* Helper function for tag comparison
* Cap short cache hashLog at 24 to prevent overflow
* size_t dictTagsMatch -> int dictTagsMatch
* nit
* Clean up and comment dictionary truncation
* Move ZSTD_tableFillPurpose_e next to ZSTD_dictTableLoadMethod_e
* Comment and expand helper functions
* Asserts and documentation
* nit
credit to oss-fuzz
This issue could happen when using the new Sequence Compression API in Explicit Delimiter Mode
with a too small dstCapacity.
In which case, there was one place where the buffer size wasn't checked.
discovered by oss-fuzz
It's a bug in the test itself :
ZSTD_compressBound() as an upper bound of the compress size
only works for data compressed "normally".
But in situations where many flushes are forcefully introduced,
this creates many more blocks,
each of which has a potential to increase the size by 3 bytes.
In extreme cases (lots of small incompressible blocks), the expansion can go beyond ZSTD_compressBound().
This situation is similar when using the CompressSequences() API
with Explicit Block Delimiters.
In which case, each explicit block acts like a deliberate flush.
When employed by a fuzzer, it's possible to generate scenarios like the one described above,
with tons of incompressible blocks of small sizes,
thus going beyond ZSTD_compressBound().
fix : when using Explicit Block Delimiters, use a larger bound, to account for this scenario.
credit to oss-fuzz
In rare circumstances, the block-splitter might cut a block at the exact beginning of a repcode.
In which case, since litlength=0, if the repcode expected 1+ literals in front, its signification changes.
This scenario is controlled in ZSTD_seqStore_resolveOffCodes(),
and the repcode is transformed into a raw offset when its new meaning is incorrect.
In more complex scenarios, the previous block might be emitted as uncompressed after all,
thus modifying the expected repcode history.
In the case discovered by oss-fuzz, the first block is emitted as uncompressed,
so the repcode history remains at default values: 1,4,8.
But since the starting repcode is repcode3, and the literal length is == 0,
its meaning is : = repcode1 - 1.
Since repcode1==1, it results in an offset value of 0, which is invalid.
So that's what the `assert()` was verifying : the result of the repcode translation should be a valid offset.
But actually, it doesn't matter, because this result will then be compared to reality,
and since it's an invalid offset, it will necessarily be discarded if incorrect,
then the repcode will be replaced by a raw offset.
So the `assert()` is not useful.
Furthermore, it's incorrect, because it assumes this situation cannot happen, but it does, as described in above scenario.
which properly represents the maximum bit size of compressed literals (11) as defined in the specification.
To be preferred from HUF_TABLELOG_DEFAULT which represents the same value but by accident.
Name selected to keep the same convention as existing width definitions,
MLFSELog, LLFSELog and OffFSELog.
the new contracts seems to make more sense :
updateRep() updates an array of repeat offsets _in place_,
while newRep() generates a new structure with the updated repeat-offset array.
Most callers are actually expecting the in-place variant,
and a limited sub-section, in `zstd_opt.c` mainly, prefer `newRep()`.
this meant to abstract the sumtype representation required
to transfert `offcode` to `ZSTD_storeSeq()`.
Unfortunately, the sumtype numeric representation is currently a leaky abstraction
that has permeated many other parts of the code,
especially within `zstd_lazy.c` and also within `zstd_opt.c` and `zstd_compress.c`.
While this PR makes a good job a transfering a large nb of call sites
to using the new macros, there are still a few sites where this transformation is more complex,
or where the numeric representation itself it used "as is".
One of the problematics area is the decision to use the numeric format of the sumtype
within the match finders of `zstd_lazy`.
This commit doesn't change the behavior, it only introduces and employes the macros,
but eventually the resulting code remains identical.
At target, if the numeric representation of the sumtype can be completely abstracted
and no other part of the code depends on it,
it will be possible to move it towards something slightly more efficient.
since this is effectively what is stored in this field (== matchLength - MINMATCH).
This makes it clearer what needs to be done when reading from / writing to this field.
This saves some 1.7Kb in rodata section (x86_64, zstd tool),
while assembler code stays the same except
the type of a few load/extend instructions.
Should not have negative performance implications.
