which now accepts an enum,
to distinguish between resetting the session, or the parameters (or both).
removed ZSTD_CCtx_resetParameters(), which is redundant.
start replacing invocation of ZSTD_CCtx_reset*() functions
Updated advanced API documentation
trimmed down amount of API staged in RC,
in particular, all functions related to ZSTD_CCtxParams()
seem too advanced.
answering #1407.
Also : removed obsolete function ZSTD_setDStreamParameter()
which could only be used with one parameter (DStream_p_maxWindowSize).
Now replaced by ZSTD_DCtx_setWindowSize() (which exists since a few revisions)
by triggering the prefetching decoder path
(which used to be dedicated to long-range offsets only).
Figures on my laptop :
no content prefetch : ~300 MB/s (for reference)
full content prefetch : ~325 MB/s (before this patch)
new prefetch path : ~375 MB/s (after this patch)
The benchmark speed is already significant,
but another side-effect is that this version
prefetch less data into memory,
since it only prefetches what's needed, instead of the full dictionary.
This is supposed to help highly active environments
such as active databases,
that can't be properly measured in benchmark environment (too clean).
Also :
fixed the largeNbDict test program
which was working improperly when setting nbBlocks > nbFiles.
not sure why it only triggers now,
this code has been around for a while.
Introduced a new error code : dstBuffer_null,
I couldn't express anything even remotely similar with existing error codes set.
changed workspace parameter convention
to always provide workspaceSize,
so that size can be explicitly checked.
Also, use more enum to make the meaning of some parameters more explicit.
isolate all logic associated with block decompression
into its own module.
zstd_decompress is still in charge
of context creation/destruction,
frames, headers, streaming, special blocks, etc.
Compressed blocks themselves are now handled within zstd_decompress_block .
fix#1385
decompressing into NULL was an automatic error.
It is now allowed, as long as the content of the frame is empty.
Seems to simplify things for `arrow`.
Maybe some other projects rely on this behavior ?
fix#1379
decodecorpus was generating one extraneous byte when `nbSeq==0`.
This is disallowed by the specification.
The reference decoder was just skipping the extraneous byte.
It is now stricter, and flag such situation as an error.
since corrupted bitstreams can generate too large values.
This slightly reduces the benefits from clang on my laptop.
gcc results and code generation are not affected.
while reviewing #1364,
I found a decompression speed improvement.
On my laptop, the new code decompresses +5-6% faster on clang
and +2-3% faster on gcc.
not bad for an accidental optimization...
note : for some reason,
scan-build version on my laptop found problems within fastcover.c
that scan-build on travisCI does not flag.
They are, as usual, false positive :
the analyzer does not understand that a table (`offset`) is correctly filled before usage.
This capability is not needed / used in the current unit of work. I'll
re-introduce it later, when we start allowing users to override the deduced
working context logs.
We pre-hash the ptr for the dict match state sometimes. When that actually
happens, a hashlog of 0 can produce undefined behavior (right shift a long
long by 64). Only applies to unoptimized compilations, since when
optimizations are applied, those hash operations are dropped when we're not
actually in dms mode.
keep one in compress_frameChunk(),
so that it's tested at every loop
in case some user simply some large mulit-GB input in a single invocation.
Add one in ZSTD_compressBlock(),
since compressBlock() explicitly skips frameChunk().
experimental function ZSTD_compressBlock() is designed for very small data in mind,
for situation where saving the ~12 bytes of frame header can actually make a difference.
Some systems though may have to deal with small and large data entangled.
If it's larger than a block (> 128KB), compressBlock() cannot compress them in one round.
That's why it's possible to compress in multiple rounds.
This is a chain of compressed blocks.
Some users push this capability to the limit, encoding gigantic chain of blocks.
On crossing the 4GB limit, some internal overflow occurs.
This fix moves the overflow correction mechanism higher in the call chain,
so that it's applied also to gigantic chains of blocks.
Added a test case in fuzzer.c, which crashes before the fix, and pass now.
which can be probed using new function ZSTD_minCLevel().
Also : redefined ZSTD_TARGETLENGTH_MIN/MAX for consistency
used the opportunity to bump version number to v1.3.6
ensure that the structure layout is as expected.
will trigger an error if it changes in the future.
Another solution would be to use a union,
this would be cleaner and get rid of these static asserts.
However, in order to keep the current code unmodified,
it would be necessary to use an un-named unions.
And apparently, un-named unions are only possible on "recent" compilers (C99+).
corresponding to the removal of workspace
which is needed while building huffman table
and is now either present in DCtx,
or temporarily borrowed from available FSE table space.
We could undersize the literals buffer by up to 11 bytes,
due to a combination of 2 bugs:
* The literals buffer didn't have `WILDCOPY_OVERLENGTH` extra
space, like it is supposed to.
* We didn't check the literals buffer size in `ZSTD_sufficientBuff()`.
* Minor fix
* Run non-optimize FASTCOVER 5 times in benchmark
* Merge fastCover into dictBuilder
* Fix mixed declaration issue
* Add fastcover to symbol.c
* Add fastCover.c and cover.h to build
* Change fastCover.c to fastcover.c
* Update benchmark to run FASTCOVER in dictBuilder
* Undo spliting fastcover_param into cover_param and f
* Remove convert param functions
* Assign f to parameter
* Add zdict.h to Makefile in lib
* Add cover.h to BUCK
* Cast 1 to U64 before shifting
* Remove trimming of zero freq head and tail in selectSegment and rebenchmark
* Remove f as a separate parameter of tryParam
* Read 8 bytes when d is 6
* Add trimming off zero frequency head and tail
* Use best functions from COVER and remove trimming part(which leads to worse compression ratio after previous bugs were fixed)
* Add finalize= argument to FASTCOVER to specify percentage of training samples passed to ZDICT_finalizeDictionary
* Change nbDmer to always read 8 bytes even when d=6
* Add skip=# argument to allow skipping dmers in computeFrequency in FASTCOVER
* Update comments and benchmarking result
* Change default method of ZDICT_trainFromBuffer to ZDICT_optimizeTrainFromBuffer_fastCover
* Add dictType enum and fix bug about passing zParam when converting to coverParam
* Combine finalize and skip into a single parameter
* Update acceleration parameters and benchmark on 3 sample sets
* Change default splitPoint of FASTCOVER to 0.75 and benchmark first 3 sample sets
* Initialize variables outside of for loop in benchmark.c
* Update benchmark result for hg-manifest
* Remove cover.h from install-includes
* Add explanation of f
* Set default compression level for trainFromBuffer to 3
* Add assertion of fastCoverParams in DiB_trainFromFiles
* Add checkTotalCompressedSize function + some minor fixes
* Add test for multithreading fastCovr
* Initialize segmentFreqs in every FASTCOVER_selectSegment and move mutex_unnlock to end of COVER_best_finish
* Free segmentFreqs
* Initialize segmentFreqs before calling FASTCOVER_buildDictionary instead of in FASTCOVER_selectSegment
* Add FASTCOVER_MEMMULT
* Minor fix
* Update benchmarking result
tells in a non-blocking way if there is something ready to flush right now.
only works with multi-threading for the time being.
Useful to know if flush speed will be limited by lack of production.
CDicts were previously guaranteed to be generated with `lowLimit=dictLimit=0`.
This is no longer true, and so the old length and index calculations are no
longer valid. This diff fixes them to handle non-zero start indices in CDicts.
When the primary normalization method fails, and
`(1 << tableLog) == (maxSymbolValue + 1)`, and every symbol gets assigned
normalized weight 1 or -1 in the first loop, then the next division can
raise `SIGFPE`.
The correct parameters are used once, but once `ZSTD_resetCStream()` is
called the default parameters (level 3) are used. Fix this by setting
`requestedParams` in the `ZSTD_initCStream*()` functions.
The added tests both fail before this patch and pass after.
[zstdmt] Fix jobsize bugs
* `ZSTDMT_serialState_reset()` should use `targetSectionSize`, not `jobSize` when sizing the seqstore.
Add an assert that checks that we sized the seqstore using the right job size.
* `ZSTDMT_compressionJob()` should check if `rawSeqStore.seq == NULL`.
* `ZSTDMT_initCStream_internal()` should not adjust `mtctx->params.jobSize` (clamping to MIN/MAX is okay).
streaming decoders, such as ZSTD_decompressStream() or ZSTD_decompress_generic(),
may end up making no forward progress,
(aka no byte read from input __and__ no byte written to output),
due to unusual parameters conditions,
such as providing an output buffer already full.
In such case, the caller may be caught in an infinite loop,
calling the streaming decompression function again and again,
without making any progress.
This version detects such situation, and generates an error instead :
ZSTD_error_dstSize_tooSmall when output buffer is full,
ZSTD_error_srcSize_wrong when input buffer is empty.
The detection tolerates a number of attempts before triggering an error,
controlled by ZSTD_NO_FORWARD_PROGRESS_MAX macro constant,
which is set to 16 by default, and can be re-defined at compilation time.
This behavior tolerates potentially existing implementations
where such cases happen sporadically, like once or twice,
which is not dangerous (only infinite loops are),
without generating an error, hence without breaking these implementations.
It's not necessary to ensure that no job is ongoing.
The pool is only expanded, existing threads are preserved.
In case of error, the only option is to return NULL and terminate the thread pool anyway.
In the new advanced API, adjust the parameters even if they are explicitly
set. This mainly applies to the `windowLog`, and accordingly the `hashLog`
and `chainLog`, when the source size is known.
There were 2 competing set of debug functions
within zstd_internal.h and bitstream.h.
They were mostly duplicate, and required care to avoid messing with each other.
There is now a single implementation, shared by both.
Significant change :
The macro variable ZSTD_DEBUG does no longer exist,
it has been replaced by DEBUGLEVEL,
which required modifying several source files.
in this version, literal compression is always disabled for ZSTD_fast strategy.
Performance parity between ZSTD_compress_advanced() and ZSTD_compress_generic()
result of ZSTD_compress_advanced()
is different from ZSTD_compress_generic()
when using negative compression levels
because the disabling of huffman compression is not passed in parameters.
The (pretty old) code inside ZSTD_compress()
was making some pretty bold assumptions
on what's inside a CCtx and how to init it.
This is pretty fragile by design.
CCtx content evolve.
Knowledge of how to handle that should be concentrate in one place.
A side effect of this strategy
is that ZSTD_compress() wouldn't check for BMI2 capability,
and is therefore missing out some potential speed opportunity.
This patch makes ZSTD_compress() use
the same initialization and release functions
as the normal creator / destructor ones.
Measured on my laptop, with a custom version of bench
manually modified to use ZSTD_compress() (instead of the advanced API) :
This patch :
1#silesia.tar : 211984896 -> 73651053 (2.878), 312.2 MB/s , 723.8 MB/s
2#silesia.tar : 211984896 -> 70163650 (3.021), 226.2 MB/s , 649.8 MB/s
3#silesia.tar : 211984896 -> 66996749 (3.164), 169.4 MB/s , 636.7 MB/s
4#silesia.tar : 211984896 -> 65998319 (3.212), 136.7 MB/s , 619.2 MB/s
dev branch :
1#silesia.tar : 211984896 -> 73651053 (2.878), 291.7 MB/s , 727.5 MB/s
2#silesia.tar : 211984896 -> 70163650 (3.021), 216.2 MB/s , 655.7 MB/s
3#silesia.tar : 211984896 -> 66996749 (3.164), 162.2 MB/s , 633.1 MB/s
4#silesia.tar : 211984896 -> 65998319 (3.212), 130.6 MB/s , 618.6 MB/s
when parameters are "equivalent",
the context is re-used in continue mode,
hence needed workspace size is not recalculated.
This incidentally also evades the size-down check and action.
This patch intercepts the "continue mode"
so that the size-down check and action is actually triggered.
recently introduce into the new dictionary mode.
The bug could be reproduced with this command :
./zstreamtest -v --opaqueapi --no-big-tests -s4092 -t639
error was in function ZSTD_count_2segments() :
the beginning of the 2nd segment corresponds to prefixStart
and not the beginning of the current block (istart == src).
This would result in comparing the wrong byte.
removed "cached" structure.
prices are now saved in the optimal table.
Primarily done for simplification.
Might improve speed by a little.
But actually, and surprisingly, also improves ratio in some circumstances.
recent experienced showed that
default distribution table for offset
can get it wrong pretty quickly with the nb of symbols,
while it remains a reasonable choice much longer for lengths symbols.
Changed the formula,
so that dynamic threshold is now 32 symbols for offsets.
It remains at 64 symbols for lengths.
Detection based on defaultNormLog
zstd rejects blocks which do not compress by at least a certain amount.
In which case, such block is simply emitted uncompressed (even if a little bit of compression could be achieved).
This is better for decompression speed, hence for energy.
The logic is controlled by ZSTD_minGain().
The rule is applied uniformly, at all compression levels.
This change makes btultra accepts blocks with poor compression ratios.
We presume that users of btultra mode prefers compression ratio over some decompress speed gains.
The threshold for minimum gain is lowered for btultra
from s>>6 (~1.5% minimum gain)
to s>>7 (~0.8% minimum gain).
This is a prudent change.
Not sure if it's large enough.
ensure that, when frequency[symbol]==0,
result is (tableLog + 1) bits
with both upper-bit and fractional-bit estimates.
Also : enable BIT_DEBUG in /tests
Work around bug in zstd decoder
Pull request #1144 exercised a new path in the zstd decoder that proved to
be buggy. Avoid the extremely rare bug by emitting an uncompressed block.
This edge case is only possible with the new optimal encoding selector,
since before zstd would always choose `set_basic` for small numbers of
sequences.
Fix `FSE_readNCount()` to support buffers < 4 bytes.
Credit to OSS-Fuzz
Estimate the cost for using FSE modes `set_basic`, `set_compressed`, and
`set_repeat`, and select the one with the lowest cost.
* The cost of `set_basic` is computed using the cross-entropy cost
function `ZSTD_crossEntropyCost()`, using the normalized default count
and the count.
* The cost of `set_repeat` is computed using `FSE_bitCost()`. We check the
previous table to see if it is able to represent the distribution.
* The cost of `set_compressed` is computed with the entropy cost function
`ZSTD_entropyCost()`, together with the cost of writing the normalized
count `ZSTD_NCountCost()`.
The cover algorithm selects one segment per epoch, and it selects the epoch
size such that `epochs * segmentSize ~= dictSize`. Selecting less epochs
gives the algorithm more candidates to choose from for each segment it
selects, and then it will loop back to the first epoch when it hits the
last one.
The trade off is that now it takes longer to select each segment, since it
has to look at more data before making a choice.
I benchmarked on the following data sets using this command:
```sh
$ZSTD -T0 -3 --train-cover=d=8,steps=256 $DIR -r -o dict && $ZSTD -3 -D dict -rc $DIR | wc -c
```
| Data set | k (approx) | Before | After | % difference |
|--------------|------------|----------|----------|--------------|
| GitHub | ~1000 | 738138 | 746610 | +1.14% |
| hg-changelog | ~90 | 4295156 | 4285336 | -0.23% |
| hg-commands | ~500 | 1095580 | 1079814 | -1.44% |
| hg-manifest | ~400 | 16559892 | 16504346 | -0.34% |
There is some noise in the measurements, since small changes to `k` can
have large differences, which is why I'm using `steps=256`, to try to
minimize the noise. However, the GitHub data set still has some noise.
If I run the GitHub data set on my Mac, which presumably lists directory
entries in a different order, so the dictionary builder sees the files in
a different order, or I use `steps=1024` I see these results.
| Run | Before | After | % difference |
|------------|--------|--------|--------------|
| steps=1024 | 738138 | 734470 | -0.50% |
| MacBook | 738451 | 737132 | -0.18% |
Question: Should we expose this as a parameter? I don't think it is
necessary. Someone might want to turn it up to exchange a much longer
dictionary building time in exchange for a slightly better dictionary.
I tested `2`, `4`, and `16`, and `4` got most of the benefit of `16`
with a faster running time.
this patch makes btultra do 2 passes on the first block,
the first one being dedicated to collecting statistics
so that the 2nd pass is more accurate.
It translates into a very small compression ratio gain :
enwik7, level 20:
blocks 4K : 2.142 -> 2.153
blocks 16K : 2.447 -> 2.457
blocks 64K : 2.716 -> 2.726
On the other hand, the cpu cost is doubled.
The trade off looks bad.
Though, that's ultimately a price to pay to reach better compression ratio.
So it's only enabled when setting btultra.
this improves compression ratio by a *tiny* amount.
It also reduces speed by a small amount.
Consequently, bit-fractional evaluation is only turned on for btultra.
ZSTD_decompress() can decompress multiple frames sent as a single input.
But the input size must be the exact sum of all compressed frames, no more.
In the case of a mistake on srcSize, being larger than required,
ZSTD_decompress() will try to decompress a new frame after current one, and fail.
As a consequence, it will issue an error code, ERROR(prefix_unknown).
While the error is technically correct
(the decoder could not recognise the header of _next_ frame),
it's confusing, as users will believe that the first header of the first frame is wrong,
which is not the case (it's correct).
It makes it more difficult to understand that the error is in the source size, which is too large.
This patch changes the error code provided in such a scenario.
If (at least) a first frame was successfully decoded,
and then following bytes are garbage values,
the decoder assumes the provided input size is wrong (too large),
and issue the error code ERROR(srcSize_wrong).
for FSE symbols.
While it seems to work, the gains are negligible compared to rough maxNbBits evaluation.
There are even a few losses sometimes, that still need to be explained.
Furthermode, there are still cases where btlazy2 does a better job than btopt,
which seems rather strange too.
for proper estimation of symbol's weights
when using dictionary compression.
Note : using only huffman costs is not good enough,
presumably because sequence symbol costs are incorrect.
Make sure that $(INCLUDEDIR) exists before copying the headers there.
Otherwise, the contest of header files is copied over
$(DESTDIR)$(INCLUDEDIR), making it a regular file.
While at it, remove $(DESTDIR)$(INCLUDEDIR) from the list of directories
to create in the install-pc target. The install-pc target does not need
this directory.
reported by @let-def.
It's actually a bug in ZSTD_compressBegin_usingCDict()
which would pass a wrong pledgedSrcSize value (0 instead of ZSTD_CONTENTSIZE_UNKNOWN)
resulting in wrong window size, resulting in downsized seqStore,
resulting in segfault when writing into the seqStore later in the process.
Added a test in fuzzer to cover this use case (fails before the patch).
The new advanced API basically set `requestedParams = appliedParams` when
using a dictionary. This halted all parameter adjustment, which can hurt
compression ratio if, for example, the window log is small for the first
call, but the rest of the files are large.
This patch fixes the bug, and checks that the `requestedParams` don't change
in the new advanced API when using a dictionary, and generally in the fuzzer.
Zstdmt uses prefixes to load the overlap between segments. Loading extra
positions makes compression non-deterministic, depending on the previous
job the context was used for. Since loading extra position takes extra
time as well, only do it when creating a `ZSTD_CDict`.
Fixes#1077.
The `avgJobSize` must not be lower than 256 KB for single-pass mode.
In `zstd.h` we say the minimum value for `ZSTD_p_jobSize` is 1 MB,
so ensure that we always pick a size >= 1 MB.
Found by libFuzzer fuzzer tests with large input limits.
this makes it possible to specify extremely large negative compression levels,
achieving the side effect as "no compression".
It will also be possible to define larger targetlength for ultra compression mode.
There is no adverse side effect due to removing this limit.
Integrate ldm into zstdmt by running it in serial and in order in the first
step of each job, in the same place as the hash gets updated. The input
buffer is sized to fit the whole LDM window and 2 full buffers of slack.
Input buffers cannot be reused until the LDM step is done with them.
After the LDM step is finished, the jobs don't actually have access to the
full window, only the overlap.
Tested on a few different multi-GB files with and without sanitizers,
and with different numbers of threads.
* Computes the XXH hash in the worker threads.
* Workers get a sequence number and wait until ther number shows up. On
error, ensures that its sequence is finished, so future threads don't
get blocked.
* Sets up for ldm integration, which will go in the same spot.
Setting `loadedDictEnd` was accidently removed from `ZSTD_loadDictionaryContent()`,
which means that dictionary compression will only be able to reference the parts of
the dictionary within the window. The spec allows us to reference the entire
dictionary so long as even one byte is in the window.
`ZSTD_enforceMaxDist()` incorrectly always allowed offsets up to `loadedDictEnd`
beyond the window, even once the dictionary was out of range.
When overflow protection kicked in, the check `current > loadedDictEnd + maxDist`
is incorrect if `loadedDictEnd` isn't reset back to zero. `current` could be reset
below the value, which would incorrectly allow references beyond the window. This
bug is present in `master`, but is very hard to trigger, since it requires both
dictionaries and data which triggers overflow correction.
Summary:
Allocate a single input buffer large enough to house each job, as well as
enough space for the IO thread to write 2 extra buffers. One goes in the
`POOL` queue, and one to fill, and then block on a full `POOL` queue.
Since we can't overlap with the prefix, we allocate space for 3 extra
input buffers.
Test Plan:
* CI
* With and without ASAN/UBSAN run zstdmt with different number of threads
on two large binaries, and verify that their checksums match.
* Test on the tip of the zstdmt ldm integration.
Reviewers: cyan
Differential Revision: https://phabricator.intern.facebook.com/D7284007
Tasks: T25664120
Summary:
* Expose the reference external sequences API for zstdmt.
Allows external sequences of any length, which get split when necessary.
* Reset the LDM window when the context is reset.
* Store the maximum number of LDM sequences.
* Sequence generation now returns the number of last literals.
* Fix sequence generation to not throw out the last literals when blocks of
more than 1 MB are encountered.
Expose reference external sequence API
* Expose the reference external sequences API for zstdmt.
* Allows external sequences of any length, which get split when necessary.
* Reset the LDM window when the context is reset.
* Store the maximum number of LDM sequences.
* Sequence generation now returns the number of last literals.
* Fix sequence generation to not throw out the last literals when blocks of
more than 1 MB are encountered.
Test Plan:
* CI
* Test the zstdmt ldm integration stacked on top of this diff
Reviewers: cyan
Differential Revision: https://phabricator.intern.facebook.com/D7283968
Tasks: T25664120
* Expose the reference external sequences API for zstdmt.
Allows external sequences of any length, which get split when necessary.
* Reset the LDM window when the context is reset.
* Store the maximum number of LDM sequences.
* Sequence generation now returns the number of last literals.
* Fix sequence generation to not throw out the last literals when blocks of
more than 1 MB are encountered.
The overflow protection is broken when the window log is `> (3U << 29)`, so 31.
It doesn't work when `current` isn't around `1U << windowLog` ahead of `lowLimit`,
and the the assertion `current > newCurrent` fails. This happens when the same
context is used many times over, but with a large window log, like in zstdmt.
Fix it by triggering correction based on `nextSrc - base` instead of `lowLimit`.
The added test fails before the patch, and passes after.
* Replaced a non-breaking space and an en dash with a plain space and
a hyphen.
* This means the files are simple ASCII and less likely to run into
codepage issues.
access negative compression levels from command line
for both compression and benchmark modes.
also : ensure proper propagation of parameters
through ZSTD_compress_generic() interface.
added relevant cli tests.
negative compression level trade compression ratio for more compression speed.
They turn off huffman compression of literals,
and use row 0 as baseline with a stepSize = -cLevel.
added associated test in fuzzer
also added : new advanced parameter ZSTD_p_literalCompression
clang only claims compatibility with gcc 4.2.
Consequently, recent patch which reserved DYNAMIC_BMI2 for gcc >= 4.8
also disabled it for clang.
fix : __clang__ is now enough to enable DYNAMIC_BMI2
(associated with other existing conditions : x64/x64, !bmi2)
which was not done properly by gcc 4.8
resulting in major performance difference.
ex :
zstd -b1 silesia.tar
before : dec 680 MB/s
after : dec 710 MB/s (without bmi2)
after : dec 770 MB/s (with DYNAMIC_BMI2)
Update code documentation, and properly names a few "magic constants".
Also, HUF_compress_internal() gets a cleaner way
to determine size of tables inside workspace.
* `ZSTD_ldm_generateSequences()` generates the LDM sequences and
stores them in a table. It should work with any chunk size, but
is currently only called one block at a time.
* `ZSTD_ldm_blockCompress()` emits the pre-defined sequences, and
instead of encoding the literals directly, it passes them to a
secondary block compressor. The code to handle chunk sizes greater
than the block size is currently commented out, since it is unused.
The next PR will uncomment exercise this code.
* During optimal parsing, ensure LDM `minMatchLength` is at least
`targetLength`. Also don't emit repcode matches in the LDM block
compressor. Enabling the LDM with the optimal parser now actually improves
the compression ratio.
* The compression ratio is very similar to before. It is very slightly
different, because the repcode handling is slightly different. If I remove
immediate repcode checking in both branches the compressed size is exactly
the same.
* The speed looks to be the same or better than before.
Up Next (in a separate PR)
--------------------------
Allow sequence generation to happen prior to compression, and produce more
than a block worth of sequences. Expose some API for zstdmt to consume.
This will test out some currently untested code in
`ZSTD_ldm_blockCompress()`.
This makes it easier to edit for maintenance and evolutions
(I plan to experiment modifications in huffman decompression functions).
The methology followed seems broadly applicable to other BMI2 modules.
Performance was tracked rigorously at each step,
there is no noticeable loss (nor win) of performance compared to `#include` version.
Note however that 4X decoder variants tend to be extremely sensitive to code alignment.
This source code resulted in pretty good performance for gcc 7.2 and 7.3,
but future changes (even in other parts of the code) might trigger the issue again.
as it's faster, due to one memory scan instead of two
(confirmed by microbenchmark).
Note : as ZSTD_reduceIndex() is rarely invoked,
it does not translate into a visible gain.
Consider it an exercise in auto-vectorization and micro-benchmarking.
On my laptop:
Before:
./zstd32 -b --zstd=wlog=27 silesia.tar enwik8 -S
3#silesia.tar : 211984896 -> 66683478 (3.179), 97.6 MB/s , 400.7 MB/s
3#enwik8 : 100000000 -> 35643153 (2.806), 76.5 MB/s , 303.2 MB/s
After:
./zstd32 -b --zstd=wlog=27 silesia.tar enwik8 -S
3#silesia.tar : 211984896 -> 66683478 (3.179), 97.4 MB/s , 435.0 MB/s
3#enwik8 : 100000000 -> 35643153 (2.806), 76.2 MB/s , 338.1 MB/s
Mileage vary, depending on file, and cpu type.
But a generic rule is : x86 benefits less from "long-offset mode" than x64,
maybe due to register pressure.
On "entropy", long-mode is _never_ a win for x86.
On my laptop though, it may, depending on file and compression level
(enwik8 benefits more from "long-mode" than silesia).
This makes it easier to explain that nbWorkers=0 --> single-threaded mode,
while nbWorkers=1 --> asynchronous mode (one mode thread on top of the "main" caller thread).
No need for an additional asynchronous mode flag.
nbWorkers>=2 works the same as nbThreads>=2 previously.
to avoid confusion with blocks.
also:
- jobs are cut into chunks of 512KB now, to reduce nb of mutex calls.
- fix function declaration ZSTD_getBlockSizeMax()
- fix outdated comment
Other job members are accessed directly.
This avoids a full job copy, which would access everything,
including a few members that are supposed to be used by worker only,
uselessly requiring additional locks to avoid race conditions.
writeLastEmptyBlock() must release srcBuffer
as mtctx assumes it's done by job worker.
minor : changed 2 job member names (src->srcBuffer, srcStart->prefixStart) for clarity
replaced by equivalent signal job->consumer == job->srcSize.
created additional functions
ZSTD_writeLastEmptyBlock()
and
ZSTDMT_writeLastEmptyBlock()
required when it's necessary to finish a frame with a last empty job, to create an "end of frame" marker.
It avoids creating a job with srcSize==0.
When ZSTD_e_end directive is provided,
the question is not only "are internal buffers completely flushed",
it is also "is current frame completed".
In some rare cases,
it was possible for internal buffers to be completely flushed,
triggering a @return == 0,
but frame was not completed as it needed a last null-size block to mark the end,
resulting in an unfinished frame.
no real consequence, but pollute tsan tests :
job->dstBuff is being modified inside worker,
while main thread might read it accidentally
because it copies whole job.
But since it doesn't used dstBuff, there is no real consequence.
Other potential solution : only copy useful data, instead of whole job
When the dictionary is <= 8 bytes, no data is loaded from the dictionary.
In this case the repcodes weren't set, because they were inserted after the
size check. Fix this problem in general by first setting the cdict state to
a clean state of an empty dictionary, then filling the state from there.
Produces 3 statistics for ongoing frame compression :
- ingested
- consumed (effectively compressed)
- produced
Ingested can be larger than consumed due to buffering effect.
For the time being, this patch mostly fixes the % ratio issue,
since it computes consumed / produced,
instead of ingested / produced.
That being said, update is not "smooth",
because on a slow enough setting,
fileio spends most of its time waiting for a worker to complete its job.
This could be improved thanks to more granular flushing
i.e. start flushing before ongoing job is fully completed.
ZSTD_create?Dict() is required to produce a ?Dict* return type
because `free()` does not accept a `const type*` argument.
If it wasn't for this restriction, I would have preferred to create a `const ?Dict*` object
to emphasize the fact that, once created, a dictionary never changes
(hence can be shared concurrently until the end of its lifetime).
There is no such limitation with initStatic?Dict() :
as stated in the doc, there is no corresponding free() function,
since `workspace` is provided, hence allocated, externally,
it can only be free() externally.
Which means, ZSTD_initStatic?Dict() can return a `const ZSTD_?Dict*` pointer.
Tested with `make all`, to catch initStatic's users,
which, incidentally, also updated zstd.h documentation.
would create too large buffers,
since default job size == window size * 4.
This would crash on 32-bit systems.
Also : jobSize being a 32-bit unsigned, it cannot be >= 4 GB,
so the formula was failing for large window sizes >= 1 GB.
Fixed now : max job Size is 2 GB, whatever the window size.
this happened on 32-bits build when requiring a too large input buffer,
typically on wlog=29, creating jobs of 2 GB size.
also : zstd32 now compiles with multithread support enabled by default
(can be disabled with HAVE_THREAD=0)
Shaves 492,076 B off of the `ZSTD_CDict`.
The size of a `ZSTD_CDict` created from a 112,640 B dictionary is:
| Level | Before (B) | After (B) |
|-------|------------|-----------|
| 1 | 648,448 | 156,412 |
| 3 | 1,140,008 | 647,932 |
This new parameter makes it possible to call
streaming ZSTDMT with a single thread set
which is non blocking.
It makes it possible for the main thread to do other tasks in parallel
while the worker thread does compression.
Typically, for zstd cli, it means it can do I/O stuff.
Applied within fileio.c, this patch provides non-negligible gains during compression.
Tested on my laptop, with enwik9 (1000000000 bytes) : time zstd -f enwik9
With traditional single-thread blocking mode :
real 0m9.557s
user 0m8.861s
sys 0m0.538s
With new single-worker non blocking mode :
real 0m7.938s
user 0m8.049s
sys 0m0.514s
=> 20% faster
it still fallbacks to single-thread blocking invocation
when input is small (<1job)
or when invoking ZSTDMT_compress(), which is blocking.
Also : fixed a bug in new block-granular compression routine.
Pathological samples may result in literal section being incompressible.
This case is now detected,
and literal distribution is replaced by one that can be written into the dictionary.
constants in zstd.h should not depend on MIN() macro which existence is not guaranteed.
Added a test to check the specific constants.
The test is a bit too specific.
But I have found no way to control a more generic "are all macro already defined" condition,
especially as this is a valid construction (the missing macro might be defined later, intentionnally).
in a new "custom memory allocator" paragraph
which is itself part of "memory management" category.
This makes it simpler to see the relation between the type and its usages.
It used to stop on reaching extDict, for simplification.
As a consequence, there was a small loss of performance each time the round buffer would restart from beginning.
It's not a large difference though, just several hundreds of bytes on silesia.
This patch fixes it.
now selected for levels 13, 14 and 15.
Also : dropped the requirement for monotonic memory budget increase of compression levels,,
which was required for ZSTD_estimateCCtxSize()
in order to ensure that a memory budget for level L is large enough for any level <= L.
This condition is now ensured at run time inside ZSTD_estimateCCtxSize().
we want the dictionary table to be fully sorted,
not just lazily filled.
Dictionary loading is a bit more intensive,
but it saves cpu cycles for match search during compression.
This is a pretty nice speed win.
The new strategy consists in stacking new candidates as if it was a hash chain.
Then, only if there is a need to actually consult the chain, they are batch-updated,
before starting the match search itself.
This is supposed to be beneficial when skipping positions,
which happens a lot when using lazy strategy.
The baseline performance for btlazy2 on my laptop is :
15#calgary.tar : 3265536 -> 955985 (3.416), 7.06 MB/s , 618.0 MB/s
15#enwik7 : 10000000 -> 3067341 (3.260), 4.65 MB/s , 521.2 MB/s
15#silesia.tar : 211984896 -> 58095131 (3.649), 6.20 MB/s , 682.4 MB/s
(only level 15 remains for btlazy2, as this strategy is squeezed between lazy2 and btopt)
After this patch, and keeping all parameters identical,
speed is increased by a pretty good margin (+30-50%),
but compression ratio suffers a bit :
15#calgary.tar : 3265536 -> 958060 (3.408), 9.12 MB/s , 621.1 MB/s
15#enwik7 : 10000000 -> 3078318 (3.249), 6.37 MB/s , 525.1 MB/s
15#silesia.tar : 211984896 -> 58444111 (3.627), 9.89 MB/s , 680.4 MB/s
That's because I kept `1<<searchLog` as a maximum number of candidates to update.
But for a hash chain, this represents the total number of candidates in the chain,
while for the binary, it represents the maximum depth of searches.
Keep in mind that a lot of candidates won't even be visited in the btree,
since they are filtered out by the binary sort.
As a consequence, in the new implementation,
the effective depth of the binary tree is substantially shorter.
To compensate, it's enough to increase `searchLog` value.
Here is the result after adding just +1 to searchLog (level 15 setting in this patch):
15#calgary.tar : 3265536 -> 956311 (3.415), 8.32 MB/s , 611.4 MB/s
15#enwik7 : 10000000 -> 3067655 (3.260), 5.43 MB/s , 535.5 MB/s
15#silesia.tar : 211984896 -> 58113144 (3.648), 8.35 MB/s , 679.3 MB/s
aka, almost the same compression ratio as before,
but with a noticeable speed increase (+20-30%).
This modification makes btlazy2 more competitive.
A new round of paramgrill will be necessary to determine which levels are impacted and could adopt the new strategy.
params1 was swapped with params2.
This used to be a non-issue when testing for strict equality,
but now that some tests look for "sufficient size" `<=`, order matters.
The deep fuzzer tests caught a subtle bug that was probably there for a long time.
The impact of the bug is not a crash, or any other clear error signal,
rather, it reduces performance, by cutting data into smaller blocks.
Eventually, the following test would fail because it produces too many 1-byte blocks,
requiring more space than buffer can provide :
`./zstreamtest_asan --mt -s3514 -t1678312 -i1678314`
The root scenario is as follows :
- Create context, initialize it using explicit parameters or a `cdict` to pin them down, set `pledgedSrcSize=1`
- The compression parameters will not be adapted, but `windowSize` and `blockSize` will be automatically set to `1`.
`windowSize` and `blockSize` are dynamic values, set within `ZSTD_resetCCtx_internal()`.
The automatic adaptation makes it possible to generate smaller contexts for smaller input sizes.
- Complete compression
- New compression with same context, using same parameters, but `pledgedSrcSize=ZSTD_CONTENTSIZE_UNKNOWN`
trigger "continue mode"
- Continue mode doesn't modify blockSize, because it used to depend on `windowLog` only,
but in fact, it also depends on `pledgedSrcSize`.
- The "old" blocksize (1) is still there,
next compression will use this value to cut input into blocks,
resulting in more blocks and worse performance than necessary performance.
Given the scenario, and its possible variants, I'm surprised it did not show up before.
But I suspect it did show up, it's just that it never triggered an error, because "worse performance" is not a trigger.
The above test is a special corner case, where performance is so impacted that it reaches an error case.
The fix works, but I'm not completely pleased.
I think the current code relies too much on implied relations between variables.
This will likely break again in the future when some related part of the code change.
Unfortunately, no time to make larger changes if we want to keep the release target for zstd v1.3.3.
So a longer term fix will have to be considered after the release.
To do : create a reliable test case which triggers this scenario for CI tests.
`zstreamtest --newapi` (and `--opaqueapi`) create and destroy way too many threads
resulting in failure of tsan tests,
and potentially connected to the qemu flaky tests.
This is because, at each test, the nb of threads can be changed (random).
The `--no-big-tests` directive reduce this choice to 1/2 threads,
in order to limit memory usage, especially for qemu and 32-bits builds.
Unfortunately, swapping between 1 and 2 threads is enough to constantly create/destroy new mtctx.
This patch takes advantage of the following property :
via compress_generic, no internal mtctx is needed for nbThreads < 2.
As a consequence, when nbThreads == 2, the currently active mtctx is necessarily good.
This dramatically reduces the nb of thread creations when invoking `zstreamtest --newapi --no-big-tests`
(only when parent cctx itself is created, which is randomized to 1/256 tests).
Expected outcome :
- at a minimum : tsan tests shall now work continuously without exploding the thread counter
- at best : flaky qemu tests on `zstreamtest --newapi --no-big-tests` may stop being flaky, due to less stress from constant thread creation/destruction
Real world impact :
minimal, I don't expect users to constantly change `nbThreads` between each invocation.
If `nbThreads` remains stable, existing implementation re-uses existing mtctx.
Also : `zstreamtest --newapi` but without `--no-big-tests` doesn't benefit as much,
since this test can select a random `nbThreads` value between 1 and 4.
The current patch only reduces opportunity to free/create mtctx (for example : 2->1->2 doesn't need a new mtctx)
but doesn't completely eliminate it, since `nbThreads` can still change between 2/3/4.
A more complete solution could be to only use 2 out of 4 allocated threads, thus keeping the pool at a constant size.
This would require a larger change to `POOL_*` api though.
taking advantage of `btopt` improved speed to tune parameters.
Levels 16-19 are stronger than previous release, making the graph more favorable.
In theory, I should also update small-size tables,
but I got lazy on that one ...
zstd streaming API was adding a null-block at end of frame for small input.
Reason is : on small input, a single block is enough.
ZSTD_CStream would size its input buffer to expect a single block of this size,
automatically triggering a flush on reaching this size.
Unfortunately, that last byte was generally received before the "end" directive (at least in `fileio`).
The later "end" directive would force the creation of a 3-bytes last block to indicate end of frame.
The solution is to not flush automatically, which is btw the expected behavior.
It happens in this case because blocksize is defined with exactly the same size as input.
Just adding one-byte is enough to stop triggering the automatic flush.
I initially looked at another solution, solving the problem directly in the compression context.
But it felt awkward.
Now, the underlying compression API `ZSTD_compressContinue()` would take the decision the close a frame
on reaching its expected end (`pledgedSrcSize`).
This feels awkward, a responsability over-reach, beyond the definition of this API.
ZSTD_compressContinue() is clearly documented as a guaranteed flush,
with ZSTD_compressEnd() generating a guaranteed end.
I faced similar issue when trying to port a similar mechanism at the higher streaming layer.
Having ZSTD_CStream end a frame automatically on reaching `pledgedSrcSize` can surprise the caller,
since it did not explicitly requested an end of frame.
The only sensible action remaining after that is to end the frame with no additional input.
This adds additional logic in the ZSTD_CStream state to check this condition.
Plus some potential confusion on the meaning of ZSTD_endStream() with no additional input (ending confirmation ? new 0-size frame ?)
In the end, just enlarging input buffer by 1 byte feels the least intrusive change.
It's also a contract remaining inside the streaming layer, so the logic is contained in this part of the code.
The patch also introduces a new test checking that size of small frame is as expected, without additional 3-bytes null block.
This patch restores capability for each file to receive adapted compression parameters depending on its size.
The bug breaking this feature was relatively silly :
setting a parameter with a value "0" is supposed to be a no-op.
Unfortunately, it would pin down compression parameters as if they were manually set,
preventing later automatic adaptation.
Unfortunately, I'm currently short of a test case that could check this situation and trigger an error.
Compression parameters selection between tableID 0,1,2,3 is largely internal,
leaving no trace to outside world, not even in frame header.
windowLog is now enforced from provided compression parameters,
instead of being copied blindly from `cdict`
where it could be smaller.
also :
- fix a minor bug in zstreamtest --mt : advanced parameters must be set before init
- changed advanced parameter name to ZSTDMT_jobSize
While the final result is still, technically, a frame,
the resulting frame expands initial data instead of compressing it.
This is because the streaming API creates a tiny 1-byte buffer for input,
because it believes input is empty (0-bytes),
because in the past, 0 used to mean "unknown" instead.
This patch fixes the issue.
Todo : add a test which traps the issue.
last such side-effect was modifying cctx->loadedDictEnd on setting forceWindow.
It is no a useless operation, so it's removed.
No side-effect left when setting a compression parameter.
Any ZSTD_CCtx_setParameter() shall just write the requested parameter, without further action.
Any action shall be taken at parameter application only (during init).
It makes it possible to just copy CCtxParams from external container to internal state,
and get rid of the more complex code which was trying to compensate for missing actions.
There was a flaw in the formula
which compared literal cost with match cost :
at a given position,
a non-null literal suite is going to be part of next sequence,
while if position ends a previous match, to immediately start another match,
next sequence will have a litlength of zero.
A litlength of zero has a non-null cost.
It follows that literals cost should be compared to match cost + litlength==0.
Not doing so gave a structural advantage to matches, which would be selected more often.
I believe that's what led to the creation of the strange heuristic which added a complex cost to matches.
The heuristic was actually compensating.
It was probably created through multiple trials, settling for best outcome on a given scenario (I suspect silesia.tar).
The problem with this heuristic is that it's hard to understand,
and unfortunately, any future change in the parser would impact the way it should be calculated and its effects.
The "proper" formula makes it possible to remove this heuristic.
Now, the problem is : in a head to head comparison, it's sometimes better, sometimes worse.
Note that all differences are small (< 0.01 ratio).
In general, the newer formula is better for smaller files (for example, calgary.tar and enwik7).
I suspect that's because starting statistics are pretty poor (another area of improvement).
However, for silesia.tar specifically, it's worse at level 22 (while being better at level 17, so even compression level has an impact ...).
It's a pity that zstd -22 gets worse on silesia.tar.
That being said, I like that the new code gets rid of strange variables,
which were introducing complexity for any future evolution (faster variants being in mind).
Therefore, in spite of this detrimental side effect, I tend to be in favor of it.
optState was used both to evaluate price
and to cache cost of previously calculated literals.
This created a strong dependency, forcing parser to request cost in a strict order.
This limitation is forbids future parser with skipping capabilities.
After this patch, caching literals price still exists,
but is now explicit, in a stack structure.
merging of repcode search into btsearch introduced a small compression ratio regressio at max level :
1.3.2 : 52728769
after repMerge patch : 52760789 (+32020)
A few minor changes have produced this difference.
They can be hard to spot.
This patch buys back about half of the difference,
by no longer inserting position at hc3 when a long match is found there.
It feels strangely counter-intuitive, but works :
after this patch : 52742555 (-18234)
Fixed : multithreading to compress some small data with dictionary
Fixed : ZSTD_initCStream_usingCDict()
Improved streaming memory usage when pledgedSrcSize is known.
ZSTD_updateTree() expected to be followed by a Bt match finder, which would update zc->nextToUpdate.
With the new optimal match finder, it's not necessarily the case : a match might be found during repcode or hash3, and stops there because it reaches sufficient_len, without even entering the binary tree.
Previous policy was to nonetheless update zc->nextToUpdate, but the current position would not be inserted, creating "holes" in the btree, aka positions that will no longer be searched.
Now, when current position is not inserted, zc->nextToUpdate is not update, expecting ZSTD_updateTree() to fill the tree later on.
Solution selected is that ZSTD_updateTree() takes care of properly setting zc->nextToUpdate,
so that it no longer depends on a future function to do this job.
It took time to get there, as the issue started with a memory sanitizer error.
The pb would have been easier to spot with a proper `assert()`.
So this patch add a few of them.
Additionnally, I discovered that `make test` does not enable `assert()` during CLI tests.
This patch enables them.
Unfortunately, these `assert()` triggered other (unrelated) bugs during CLI tests, mostly within zstdmt.
So this patch also fixes them.
- Changed packed structure for gcc memory access : memory sanitizer would complain that a read "might" reach out-of-bound position on the ground that the `union` is larger than the type accessed.
Now, to avoid this issue, each type is independent.
- ZSTD_CCtxParams_setParameter() : @return provides the value of parameter, clamped/fixed appropriately.
- ZSTDMT : changed constant name to ZSTDMT_JOBSIZE_MIN
- ZSTDMT : multithreading is automatically disabled when srcSize <= ZSTDMT_JOBSIZE_MIN, since only one thread will be used in this case (saves memory and runtime).
- ZSTDMT : nbThreads is automatically clamped on setting the value.
this version has same speed as branch `opt`
which is itself 5-10% slower than branch `dev`
(no identified reason)
It does not compress exactly the same as `opt` or `dev`,
maybe because it doesn't stop search after repcodes,
leading to sometimes better compression, sometimes worse
(by a small margin).
warning : _extDict path does not work for the time being
This means that benchmark module works,
but file module will fail with large files (and high compression level).
Objective is to fuse _extDict path into current one,
in order to have a single parser to maintain.
ZSTD_getPrice() and ZSTD_updatePrice() accept normal matchlength as argument
instead of matchlength-MINMATCH,
which makes them easier / more logical to use and read.
Conversion is simply done internally.
added some traces and assert
related to hunting a potential ubsan error in 32-bits more
(it ends up being a compiler-side issue : https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82802).
Modified one pointer arithmetic expression for a more conformant way.
as per documentation, on ZSTD_setPledgedSrcSize() :
> If all data is provided and consumed in a single round,
> this value (pledgedSrcSize) is overriden by srcSize instead.
This wasn't applied before compression level is transformed into compression parameters.
As a consequence, small input missed compression parameters adaptation.
It seems to work fine now : compression was compared with ZSTD_compress_advanced(),
results were the same.
ZSTD_compress() and friends would treat an empty input as an unknown size
when selecting parameters. Thus, they would drastically overallocate the
context. Tell ZSTD_getParams() that the source size is 1 when it is empty.
it was invoking ZSTD_initCStream_advanced() with pledgedSrcSize==0 and contentSizeFlag=1
which means "empty"
while the intention was to mean "unknown".
The contentSizeFlag==1 is new, it is a consequence of setting this value to 1 by default.
The solution selected here is to pass ZSTD_CONTENTSIZE_UNKNOWN to mean "unknown".
So contentSizeFlag remains set (it wasn't in previous versions).
It was multiple reasons stacked :
- Visual use a different code path, because ZSTD_NEWAPI is not defined
- fileio.c sends `0` as `pledgedSrcSize` to mean `ZSTD_CONTENTSIZE_UNKNOWN` (fixed)
- ZSTDMT_resetCCtx() interpreted `0` as "empty" instead of "unknown" (fixed)
It isn't useful in any case to repeat default tables.
Saves a few bytes on Silesia, since we don't trigger the dictionary
heuristic.
Before: 211988480 => 73651998 bytes
After: 211988480 => 73651721 bytes
when determining compression parameters
to compress one file only.
For multiple files, it still "bets" that files are going to be small.
There was also a bug recently added in ZSTD_CCtx_loadDictionary_advanced()
making it incapable to use pledgedSrcSize to determine compression parameters.
to mean "pledgedSrcSize is not known at init time" instead of `0`.
Note that, a few prototypes created and documented with `0` to mean "unknown" still interpret "0" as unknown,
to avoid breaking 3rd party applications which depend on this behavior.
But this value is no longer recommended to mean "unknown".
In some future version, it might be possible to switch "0" to mean "empty",
as is already the case for several prototypes.
The advantage is that pledgedSrcSize field would have same behavior accross entire API,
making it easier to reason about.
Note that all concerned prototypes belong to the "experimental" API section.
srcSize is controlled at end of compression,
so if someone uses "0" to mean "unknown" while it effectively means "empty",
this is immediately caught by the compression function, which generates an error code : ZSTD_ERROR_srcSize_wrong
In `ZSTD_compressBegin_advanced()`, `ZSTD_parameters` are used to set the
compression parameters, but the level didn't get set to `CLEVEL_CUSTOM`, so
`ZSTD_compressBlock()` used the wrong parameters when checking the source
size.
ZSTD_compressBound() works fine, but is only useful for dynamic allocation.
For static allocation, only a macro can provide the amount during compilation time.
It's not good to mix old and new API
ZSTD_resetCStream() doesn't just set pledgedSrcSize :
it also sets the CCtx for a single thread compression.
Problem is, when 2+ threads are defined in cctx->requestedParams,
ZSTD_compress_generic() will want to start MT compression,
since initialization is supposed to have already happened (thanks to ZSTD_resetCStream())
except that the underlying ZSTDMT_CCtx* object is not created,
resulting in a segfault.
This is an invalid construction
(correct one is to use ZSTD_CCtx_setPledgedSrcSize()).
I haven't found a nice way to mitigate this impact if someone makes the same mistake.
At some point, removing the old API to keep only the new API within fileio.c will limit these risks.
srcSize is read and provided at each file, not at resource creation.
This used to be useful with older API, because it could not re-adapt parameters between sessions.
At some point, it will be better to remove the old code, and only keep the new_api.
It works fine by now.
In some complex scenario,
the buffer would be freed because it's too large,
another buffer would be allocated, but fail,
trigger an error,
and the general buffer pool would then be freed,
where the definition of the already freed buffer would be found
(beyond total index, but still), and freed again, resulting in double-free error.
It would previously exit when srcSize is unknown.
But in the case of custom parameters,
hLog and cLog can still be too large in comparison with windowLog.
Reduces maximum memory allocated during zstreamtest --newapi
It does not feel "right" from a dependency perspective.
ZSTD_initDCtx_internal() is triggered once, on DCtx creation,
while ZSTD_decompressBegin() is invoked at the beginning of each new frame,
and is also a user-facing prototype.
Downside : a DCtx must be init before first usage !
This was always the intention by the way, and is documented as such.
This stage is automatically done within ZSTD_decompress() and variants,
and also within ZSTD_decompressStream().
Only ZSTD_decompressContinue() is impacted,
it must be preceded by a ZSTD_decompressBegin(), as detailed in doc.
A test has been fixed, to no longer rely on undocumented assumption that ZSTD_decompressBegin() is invoked during init.
decoder output buffer would receive a wrong size.
In previous version, ZSTD_decompressStream() would blindly trust the caller that pos <= size.
In this version, this condition is actively checked,
and the function returns an error code if this condition is not respected.
This check could also be done with an assert(),
but since this is a user-facing interface, it seems better to keep this check at runtime.
* Maximum window size in 32-bit mode is 1GB, since allocations for 2GB fail
on my Mac.
* Maximum window size in 64-bit mode is 2GB, since that is the largest
power of 2 that works with the overflow prevention.
* Allow `--long=windowLog` to set the window log, along with
`--zstd=wlog=#`. These options also set the window size during
decompression, but don't override `--memory=#` if it is set.
* Present a helpful error message when the window size is too large during
decompression.
* The long range matcher defaults to a hash log 7 less than the window log,
which keeps it at 20 for window log 27.
* Keep the default long range matcher window size and the default maximum
window size at 27 for the API and CLI.
* Add tests that use the maximum window size and hash size for compression
and decompression.
resulting in undefined symbol error.
Push the requirement to GCC 4 for now.
Another solution, proposed by @NWilson, is to use __LONG_MAX__ instead.
__LONG_MAX__ is a GCC-specific constant, which value is supposed to depend on underlying target hardware (32/64 bits)
Might be better, but seems also more complex, hence more prone to side effects.
Keeping the simple solution for now (just rely on __GNUC__)
supporting function for bufferless streaming API (ZSTD_decompressContinue())
makes it possible to correctly size a round buffer for decoding using this API.
also : added field blockSizeMax within ZSTD_frameHeader,
as it's a necessary information to know when to restart at beginning of decoding buffer.
The zstd format specification doesn't enforce that Huffman compressed
literals (including the table) have to be smaller than the uncompressed
literals. The compressor will never Huffman compress literals if the
compressed size is larger than the uncompressed size. The decompresser
doesn't accept Huffman compressed literals with 4 streams whose compressed
size is at least as large as the uncompressed size.
* Make the decompresser accept Huffman compressed literals whose size
increases.
* Add a test case that exposes the bug. The compressed file has to be
statically generated, since the compressor won't normally produce files
that expose the bug.
If the destination buffer is the minimum allowed size in
`ZSTD_compressSequences()` (2^17), then if the block isn't compressible
compression might fail with `dstSize_tooSmall`, when it should instead emit
a raw uncompressed block.
Additionally, `ZSTD_compressLiterals()` implicitly called
`ZSTD_noCompressLiterals()` if Huffman compression failed. Make that
explicit.
Note : all error codes are changed by this new version,
but it's expected to be the last change for existing codes.
Codes are now grouped by category, and receive a manually attributed value.
The objective is to guarantee that
error code values will not change in the future
when introducing new codes.
Intentionnal empty spaces and ranges are defined
in order to keep room for potential new codes.
Previously, each job would reserve a CCtx right before being posted.
The CCtx would be "part of the job description",
and only released when the job is completed (aka flushed).
For ZSTDMT_compress(), which creates all jobs first and only join at the end,
that meant one CCtx per job.
The nb of jobs used to be == nb of threads,
but since latest modification,
which reduces the size of jobs in order to spread the load of difficult areas,
it also increases the nb of jobs for large sources / small compression level.
This resulted in many more CCtx being created.
In this new version, CCtx are reserved within the worker thread.
It guaranteea there cannot be more CCtx reserved than workers (<= nb threads).
To do that, it required to make the CCtx Pool multi-threading-safe :
it can now be called from multiple threads in parallel.
Makes frame type (zstd,skippable) detection more straighforward.
ZSTD_getFrameHeader set frameContentSize=ZSTD_CONTENTSIZE_UNKNOWN to mean "field not present"
* `ZSTD_decompressStream_generic()` `ip` may be `NULL` for one of the calls
to `memcpy()`
* Assert the source is not `NULL` for calls to `memcpy()` where I believe
the source should not be `NULL`.
switch to single-pass mode directly into output buffer
when outputSize >= ZSTD_compressBound(inputSize).
Speed gains observed with fullbench (~+15% on level 1)
use less macro statements
the initial version was meant to work with STATIC_ASSERT
but since it doesn't work and needs assert()
it's possible to rewrite it using normally compiled code
which is better for compiler.
Downside : the error message is less precise.
There is a DEBUGLOG(3,) to compensate.
ZSTD_estimateCDictSize() now uses same arguments as ZSTD_createCDict()
ZSTD_estimateCDictSize_advanced() uses same arguments as ZSTD_createCDict_advanced()
ZSTD_estimateCCtx() is now a "simple" function,
taking int compressionLevel as single argument.
ZSTD_estimateCCtx_advanced() takes a CParams argument,
which is both more complete and more complex to generate.
Doesn't speed optimize this buffer-to-buffer scenario yet.
Still internally defers to streaming implementation.
Also : fixed a long standing bug in ZSTDMT streaming API.
initially uses calloc() instead of memset().
Performance improvement is unlikely measurable,
since ZSTD_CCtx is now very small,
with all tables transferred into workSpace.
now ZSTD_customCMem is promoted as new default.
Advantages : ZSTD_customCMem = { NULL, NULL, NULL},
so it's natural default after a memset.
ZSTD_customCMem is public constant
(defaultCustomMem was private only).
Also : makes it possible to introduce ZSTD_calloc(),
which can now default to stdlib's calloc()
when it detects system default.
Fixed zlibwrapper which depended on defaultCustomMem.
memset() was a quick fix to initialization problems,
but initialize too much space (tables, buffers)
which show up in decompression speed of ZSTD_decompress()
since it needs to recreate DCtx at each invocation.
Fixed by only initialization relevant pointers and size fields.
They are now the same object.
It's recommended to keep both types in source code
as previous versions of library (<v1.3.0)
still need this differentiation.
Everything converge towards ZSTD_compressBegin_internal
which delegated to ZSTD_copyCCtx_internal if cdict!=NULL.
This simplifies routing which was previously depending on cdict.
It makes it more difficult to directly cast the result of a function,
requiring to store the result in an intermediate variable.
It does not necessarily help readability,
and this restriction can be difficult to overcome in some constructions,
like some macros.
also : fixed minor Visual conversion warnings in datagencli.c
The following warning appears during build at sevaral places.
../lib/legacy/zstd_v04.c:819:40: warning: this statement may fall through [-Wimplicit-fallthrough=]
case 7: bitD->bitContainer += (size_t)(((const BYTE*)(bitD->start))[6]) << (sizeof(size_t)*8 - 16);
../lib/legacy/zstd_v05.c:821:40: warning: this statement may fall through [-Wimplicit-fallthrough=]
case 7: bitD->bitContainer += (size_t)(((const BYTE*)(bitD->start))[6]) << (sizeof(size_t)*8 - 16);
../lib/legacy/zstd_v06.c:913:40: warning: this statement may fall through [-Wimplicit-fallthrough=]
case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) << (sizeof(bitD->bitContainer)*8 - 16);
../lib/legacy/zstd_v07.c:583:40: warning: this statement may fall through [-Wimplicit-fallthrough=]
case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) <<
(sizeof(bitD->bitContainer)*8 - 16);
Signed-off-by: Jos Collin <jcollin@redhat.com>
The following warning appears during build.
../lib/compress/huf_compress.c: In function ‘HUF_compress1X_usingCTable’:
../lib/compress/huf_compress.c:444:8: warning: this statement may fall through [-Wimplicit-fallthrough=]
if (sizeof((stream)->bitContainer)*8 < HUF_TABLELOG_MAX*4+7) HUF_FLUSHBITS(stream)
^
../lib/compress/huf_compress.c:465:18: note: in expansion of macro ‘HUF_FLUSHBITS_2’
HUF_FLUSHBITS_2(&bitC);
^~~~~~~~~~~~~~~
../lib/compress/huf_compress.c:466:9: note: here
case 2 : HUF_encodeSymbol(&bitC, ip[n+ 1], CTable);
../lib/compress/zstd_compress.c: In function ‘ZSTD_compressStream_generic’:
../lib/compress/zstd_compress.c:3366:34: warning: this statement may fall through [-Wimplicit-fallthrough=]
zcs->streamStage = zcss_flush; /* pass-through to flush stage */
~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
../lib/compress/zstd_compress.c:3369:9: note: here
case zcss_flush:
Signed-off-by: Jos Collin <jcollin@redhat.com>
The following warning appears during the build. Fixed the review comments too.
zstd/lib/common/bitstream.h: In function ‘BIT_initDStream’:
zstd/lib/common/bitstream.h:277:33: warning: this statement may fall through [-Wimplicit-fallthrough=]
case 7: bitD->bitContainer += (size_t)(((const BYTE*)(srcBuffer))[6]) <<
(sizeof(bitD->bitContainer)*8 - 16);
Signed-off-by: Jos Collin <jcollin@redhat.com>
* upstream/dev: (305 commits)
added test for ZSTD_estimateCStreamSize()
changed variable name, for clarity
fixed ZSTD_estimateCStreamSize()
shortened ZSTD_createCStream_Advanced()
fixed symbols test
added ZSTD_estimateDStreamSize()
changed name frameParams into frameHeader
regroup memory usage function declarations
separated ZSTD_estimateCStreamSize() from ZSTD_estimateCCtxSize()
bumped version number
added ZSTD_estimateCDictSize() and ZSTD_estimateDDictSize()
Updated ZSTD_freeCCtx()
updated ZSTD_estimateCCtxSize()
Updated ZSTD_sizeof_CCtx()
merged CCtx and CStream as a single same object
cli : -d and -t do not stop after a failed decompression
added dev branch CircleCI badge
added dev branch Appveyor badge
keep dev branch status only
creates a binary archive without the `programs` directory
...
ZSTD_frameParams => ZSTD_frameHeader
ZSTD_getFrameParams() -> ZSTD_getFrameHeader()
The new naming is more distinctive from ZSTD_frameParameters,
which is used during compression.
ZSTD_frameHeader is clearer in its intention to described frame header content.
It also implies we are decoding a ZSTD frame, hence we are at decoding stage.
added a parameter streaming,
to estimate memory allocation size
when the CCtx is used for streaming (CStream).
Note : this function is not able to estimate
memory cost of a potential internal CDict
which can only happen when starting with ZSTD_initCStream_usingDict()
It inflates binary sizes, which is negative for the Windows build.
It also makes it impossible to check if 2 different source codes
get nonetheless compiled to the same binary,
since checksum will be different, due to integrated source code.
Previous -18 : 4.7 MB/s, R:3.833
New -18 : 5.1 MB/s. R:3.825
It's a better fit within -17 (6.8 MB/s) and -19 (4.0 MB/s)
The new level 18 also uses significantly less memory.
And, it makes a good transition between level 17 (mml5)
and level 19 (mml3).
Up to now, there was no level with mml4.
(note : minmatch setting can have a large impact on some (specific) datasets)
It now only uses compressionParameters as argument.
It produces many changes throughout user code,
though hopefully they tend to be simple :
just provide the cParams part from existing ZSTD_parameters.
Some programs might depend on ZSTD_createCDict_advanced() to pass frame parameters.
This change will force them to revisit this strategy and fix it,
since frame parameters are effectively silently ignored in current version.
clearer separation between variables and buffers
clearer buffers category
kept static buffers at the beginning, favoring cache locality
(it will be easier to add FSE tables there later)
This break a few assumptions that hashTable was always at the beginning.
This is fixed.
And remaining assumptions (namely that tables stand next to each other in memory)
are now tested with assert.
because by definition srcSize is not known when using this prototype.
added relevant test
Note : this use was already working, because at a later stage
(both ZSTD_compressBegin_usingCDict() and ZSTD_copyCCtx())
pledgedSrcSize=0 is translated into "unknown", no matter the frame parameter.
This is not correct, but of little importance,
as the medium term plan is to no longer set fParams within CDict
This is now the regroup point for ZSTD_initCStream*() functions
ZSTD_initCStream_advanced() now properly checks for parameters validity.
Also : added <assert.h> usage inside zstd_compress.c
Needs ZSTD_DEBUG=1 macro to be triggered.
Will be triggered by default from `tests` directory
does no longer allocate temporary buffers
when there is enough room in dstBuffer to decompress directly there.
(previous method would skip that for 1st chunk only).
Also : fix ZSTD_compressBound() for small srcSize
required so that if Total = A+B
compressBound(Total) <= compressBound(A) + compressBound(B)
under condition of a minimum size for A and B
Will help for ZSTDMT_compress() memory allocation
Method 1 __packed is always as good or better than memcpy().
But it's not portable, as it depends on compiler extension.
For gcc, __pakced directive works fine.
Furthermore, gcc has serious performance issues with memcpy() on ARM 32 bits.
See #620
now works with the `=` variant, which is the recommended one.
Old variant `--dictID #` still works, for compatibility with existing scripts.
Long term objective is to remove the old variant..
forgot to add the dictionary content
(tests were not failing, just compressing less).
Also : added size protections when adding dict content
since hc/bt table filling would fail if size < 8
The compressor always reuses the existing Huffman table if the literals
size is at most 1 KiB. If the compression strategy is `ZSTD_lazy` or
stronger always check to see if reusing the previous table or creating
a new table is better.
This doesn't yet weigh in decompression speed. I don't want to add any
heuristics there until I have real data to work with to ensure that the
heuristic works for at least one use case, preferably more.
This decoder variant is detrimental to x86 architecture
likely due to register pressure.
Note that the variant is disabled for all 32-bits targets.
It's unclear if it would help for different architectures,
such as ARM, MIPS or PowerPC.
* Compressor saves most recently used Huffman table and reuses it
if it produces better results.
* I attempted to preserve CPU usage profile.
I intentionally left all of the existing heuristics in place.
There is only a speed difference on the second block and later.
When compressing large enough blocks (say >= 4 KiB) there is
no significant difference in compression speed.
Dictionary compression of one block is the same speed for blocks
with literals <= 1 KiB, and after that the difference is not
very significant.
* In the synthetic data, with blocks 10 KB or smaller, most blocks
can't use repeated tables because the previous block did not
contain a symbol that the current block contains.
Once blocks are about 12 KB or more, most previous blocks have
valid Huffman tables for the current block, and the compression
ratio and decompression speed jumped.
* In silesia blocks as small as 4KB can frequently reuse the
previous Huffman table (85%), but it isn't as profitable, and
the previous Huffman table only gets used about 3% of the time.
* Microbenchmarks show that `HUF_validateCTable()` takes ~55 ns
and `HUF_estimateCompressedSize()` takes ~35 ns.
They are decently well optimized, the first versions took 90 ns
and 120 ns respectively. `HUF_validateCTable()` could be twice as
fast, if we cast the `HUF_CElt*` to a `U32*` and compare to 0.
However, `U32` has an alignment of 4 instead of 2, so I think that
might be undefined behavior.
* I've ran `zstreamtest` compiled normally, with UASAN and with MSAN
for 4 hours each.
The worst case for the speed difference is a bunch of small blocks
in the same frame. I modified `bench.c` to compress the input in a
single frame but with blocks of the given block size, set by `-B`.
Benchmarks on level 1:
| Program | Block size | Corpus | Ratio | Compression MB/s | Decompression MB/s |
|-----------|------------|-----------|-------|------------------|--------------------|
| zstd.base | 256 | synthetic | 2.364 | 110.0 | 297.0 |
| zstd | 256 | synthetic | 2.367 | 108.9 | 297.0 |
| zstd.base | 256 | silesia | 2.204 | 93.8 | 415.7 |
| zstd | 256 | silesia | 2.204 | 93.4 | 415.7 |
| zstd.base | 512 | synthetic | 2.594 | 144.2 | 420.0 |
| zstd | 512 | synthetic | 2.599 | 141.5 | 425.7 |
| zstd.base | 512 | silesia | 2.358 | 118.4 | 432.6 |
| zstd | 512 | silesia | 2.358 | 119.8 | 432.6 |
| zstd.base | 1024 | synthetic | 2.790 | 192.3 | 594.1 |
| zstd | 1024 | synthetic | 2.794 | 192.3 | 600.0 |
| zstd.base | 1024 | silesia | 2.524 | 148.2 | 464.2 |
| zstd | 1024 | silesia | 2.525 | 148.2 | 467.6 |
| zstd.base | 4096 | synthetic | 3.023 | 300.0 | 1000.0 |
| zstd | 4096 | synthetic | 3.024 | 300.0 | 1010.1 |
| zstd.base | 4096 | silesia | 2.779 | 223.1 | 623.5 |
| zstd | 4096 | silesia | 2.779 | 223.1 | 636.0 |
| zstd.base | 16384 | synthetic | 3.131 | 350.0 | 1150.1 |
| zstd | 16384 | synthetic | 3.152 | 350.0 | 1630.3 |
| zstd.base | 16384 | silesia | 2.871 | 296.5 | 883.3 |
| zstd | 16384 | silesia | 2.872 | 294.4 | 898.3 |
Previously,
followed by :
would fail to include the static definitions,
because the second include was simply skipped by guard macro.
Now it works as intended :
the missing static part is included during the second include.
XXH_STATIC_LINKING_ONLY protection macro is intended to be triggered just before the include.
The main idea is to keep this setting local :
user module shall explicitly understand and accept the static linking restriction
which becomes transparent when triggering the macro at project level.
Global definition also triggers redefinition warnings for user modules which do locally define the macro.
This new version compiles lib and cli without warning when the macro is set globally.
That's not a scenario to be recommended, since it trades a local effect for a global one,
but it was easy enough to provide from zstd side.
When ZSTD_decompressStream() detects
that there is enough space in dst
to complete decompression in a single pass,
delegates to ZSTD_decompress(),
for an extra ~5% speed boost
There used to be a (very small) chance that
loading prefix from previous segment
would be confused with a real zstd dictionary.
For that to happen, the prefix needs to start
with the same value as dictionary magic.
That's 1 chance in 4 billions if all values have equal probability.
But in fact, since some values are more common (0x00000000 for example)
others are less common, and dictionary magic was selected to be one of them,
so probabilities are likely even lower.
Anyway, this risk is no down to zero
by adding a new CCtx parameter : ZSTD_p_forceRawDict
Current parameter policy : the parameter "stick" to its CCtx,
so any dictionary loading after ZSTD_p_forceRawDict is set
will be loaded in "raw" ("content only") mode,
even if CCtx is re-used multiple times with multiple different dictionary.
It's up to the user to reset this value differently if it needs so.
Reproduction steps:
```
make zstreamtest CC=clang CFLAGS="-O3 -g -fsanitize=memory -fsanitize-memory-track-origins"
./zstreamtest -vv -t4178 -i4178 -s4531
```
How to get to the error in gdb (may be a more efficient way):
* 2 breaks at zstd_compress.c:2418 -- in ZSTD_compressContinue_internal()
* 2 breaks at zstd_compress.c:2276 -- in ZSTD_compressBlock_internal()
* 1 break at zstd_compress.c:1547
Why the error occurred:
When `zc->forceWindow == 1`, after calling `ZSTD_loadDictionaryContent()` we
have `zc->loadedDictEnd == zc->nextToUpdate == 0`. But, we've really loaded up
to `iend` into the dictionary. Then in `ZSTD_compressBlock_internal()` we see
that `current > zc->nextToUpdate + 384`, so we load the last 192 bytes a second
time. In this case the bytes we are loading are a block of all 0s, starting in
the previous block. So when we are loading the last 192 bytes, we find a `match`
in the future, 183 bytes beyond `ip`. Since the block is all 0s, the match
extends to the end of the block. But in `ZSTD_count()` we only check that
`pIn < pInLoopLimit`, but since `pMatch > pIn`, `pMatch` eventually points past
the end of the buffer, causing the MSAN failure.
The fix:
The line changed sets sets `zc->nextToUpdate` to the end of the dictionary.
This is the behavior that existed before `ZSTD_p_forceWindow` was introduced.
This fixes the exposing test case. Since the code doesn't fail without
`zc->forceWindow`, it makes sense that this works. I've run the command
`./zstreamtest -T2mn` 64 times without failures. CI should also verify nothing
obvious broke.
- Add ZSTD_findDecompressedSize
- Traverses multiple frames to find total output size
- Add ZSTD_getFrameContentSize
- Gets the decompressed size of a single frame by reading header
- Deprecate ZSTD_getDecompressedSize
the minimum size condition size is applied transparently (no warning, no error)
like previous minimum section size condition (1 KB) which still applies.
Previous version was requiring a fairly large initial amount of input data
before starting to create compression jobs.
This new version starts the process much sooner.
* dev:
updated NEWS
fixed MSAN warnings in legacy decoders
Fix cmake build
updated NEWS
Edits as per comments, and change wildcard 'X' to '?'
Fix Visual Studios project
Fix pool.c threading.h import
Fix zstdmt_compress.h include
Fixed commented issues
Updated format specification to be easier to understand
improved #232 fix
Fixed https://github.com/facebook/zstd/issues/232
.travis.yml: different tests for "master" branch
.travis.yml: optimized order of short tests
.travis.yml: test jobs 12-15
JOB_NUMBER -eq 9
improved ZSTD_compressBlock_opt_extDict_generic
In some extraordinary circumstances,
*Length field can be generated from reading a partially uninitialized memory segment.
Data is correctly identified as corrupted later on,
but the read taints some later pointer arithmetic operation.
fileio.c was continually pushing more content without giving a chance to flush compressed one.
It would block the job queue when input data was accumulated too fast (requiring to define many threads).
Fixed : fileio flushes whatever it can after each input attempt.
Sections 2+ read a bit of data from previous section
in order to improve compression ratio.
This also costs some CPU, to reference read data.
Read data is currently fixed to window>>3 size
By default, section sizes are 4x window size.
This new setting allow manual selection of section sizes.
The larger they are, the (slightly) better the compression ratio,
but also the higher the memory allocation cost,
and eventually the lesser the nb of possible threads,
since each section is compressed by a single thread.
It also introduces a prototype to set generic parameters,
ZSTDMT_setMTCtxParameter()
The idea is that it's possible to add enums
to extend the list of parameters that can be set this way.
This is more long-term oriented than a fixed-size struct.
Consider it as a test.
In some (rare) cases, job list could be blocked by a first job still being processed,
while all following ones are completed, waiting to be flushed.
In such case, the current job-table implementation is unable to accept new job.
As a consequence, a call to ZSTDMT_compressStream() can be useless (nothing read, nothing flushed),
with the risk to trigger a busy-wait on the caller side
(needlessly loop over ZSTDMT_compressStream() ).
In such a case, ZSTDMT_compressStream() will block until the first job is completed and ready to flush.
It ensures some forward progress by guaranteeing it will flush at least a part of the completed job.
Energy-wasting busy-wait is avoided.
Like ZSTD_initCStream_usingDict(),
ZSTDMT_initCStream_usingDict() now keep a copy of dict internally.
This way, dict can be released :
it does not longer have to outlive all future compression sessions.
Correctly compress with custom params and dictionary
Added relevant fuzzer test in zstreamtest
Also :
new macro ZSTDMT_SECTION_LOGSIZE_MIN, which sets a minimum size for a full job
(note : a flush() command can still generate a partial job anytime)
Also : fixed corner case, where nb of jobs completed becomes > jobQueueSize
which is possible when many flushes are issued
while there is not enough dst buffer to flush completed ones.
MT compression generates a single frame.
Multi-threading operates by breaking the frames into independent sections.
But from a decoder perspective, there is no difference :
it's just a suite of blocks.
Problem is, decoder preserves repCodes from previous block to start decoding next block.
This is also valid between sections, since they are no different than changing block.
Previous version would incorrectly initialize repcodes to their default value at the beginning of each section.
When using them, there was a mismatch between encoder (default values) and decoder (values from previous block).
This change ensures that repcodes won't be used at the beginning of a new section.
It works by setting them to 0.
This only works with regular (single segment) variants : extDict variants will fail !
Fortunately, sections beyond the 1st one belong to this category.
To be checked : btopt strategy.
This change was only validated from fast to btlazy2 strategies.
In some complex scenarios (free() without finishing compression),
it is possible that some resources are still into jobs
and not collected back into pools.
In which case, previous version of free() would miss them.
This would be equivalent to a leak.
New version ensures that it even foes after such resource.
It requires job consumers to properly mark resources as released,
by replacing entries by NULL after releasing back to the pool.
Obviously, it's not recommended to free() zstdmt context mid-term,
still that's now a supported scenario.
The same methodology is also used to ensure proper resource collection
after an error is detected.
Still to do :
- detect compression errors (not just allocation ones)
- properly manage resource when init() is called without finishing previous compression.
The main issue was to avoid a caller to continually loop on {flush,end}Stream()
when there was nothing ready to be flushed but still some compression work ongoing in a worker thread.
The continuous loop would have resulted in wasted energy.
The new version makes call to {flush,end}Stream blocking when there is nothing ready to be flushed.
Of course, if all worker threads have exhausted job, it will return zero (all flush completed).
Note : There are still some remaining issues to report error codes
and properly collect back resources into pools when an error is triggered.
When porting python-zstandard to use ZSTD_initCStream_usingCDict()
so compression dictionaries could be reused, an automated test
failed due to compressed content changing.
I tracked this down to ZSTD_initCStream_usingCDict() not
setting the dictID field of the ZSTD_CCtx attached to the
ZSTD_CStream instance.
I'm not 100% convinced this is the correct or full solution,
as I'm still seeing one automated test failing with this change.
In previous version, main function would return early when detecting a job error.
Late threads resources were therefore not collected back into pools.
New version just register the error, but continue the collecting process.
All buffers and context should be released back to pool before leaving main function.
Result from getBuffer and getCCtx could be NULL when allocation fails.
Now correctly checks : job creation stop and last job reports an allocation error.
releaseBuffer and releaseCCtx are now also compatible with NULL input.
Identified a new potential issue :
when early job fails, later jobs are not collected for resource retrieval.
Since the result of mt compression is a single frame,
changed naming, which implied the concatenation of multiple frames.
minor : ensures that content size is written in header
The new strategy involves cutting frame at block level.
The result is a single frame, preserving ZSTD_getDecompressedSize()
As a consequence, bench can now make a full round-trip,
since the result is compatible with ZSTD_decompress().
This strategy will not make it possible to decode the frame with multiple threads
since the exact cut between independent blocks is not known.
MT decoding needs further discussions.
use ZSTD_freeCCtxPool() to release the partially created pool.
avoids to duplicate logic.
Also : identified a new difficult corner case :
when freeing the Pool, all CCtx should be previously released back to the pool.
Otherwise, it means some CCtx are still in use.
There is currently no clear policy on what to do in such a case.
Note : it's supposed to never happen.
Since pool creation/usage is static, it has no external user,
which limits risks.
`ZDICT_finalizeDictionary()` had a flipped comparison.
I also allowed `dictBufferCapacity == dictContentSize`.
It might be the case that the user wants to fill the dictionary
completely up, and then let zstd take exactly the space it needs
for the entropy tables.
execSequence relied on pointer overflow to handle cases where
`sequence.matchLength < 8`. Instead of passing an `size_t` to
wildcopy, pass a `ptrdiff_t`.
Allows an adversary to write up to 3 bytes beyond the end of the buffer.
Occurs if the match overlaps the `extDict` and `currentPrefix`, and the
match length in the `currentPrefix` is less than `MINMATCH`, and
`op-(16-MINMATCH) >= oMatchEnd > op-16`.
When the overflow protection kicks in, it makes sure that ip - ctx->base
isn't too large. However, it didn't ensure that saved offsets are
still valid. This change ensures that any valid offsets (<= windowLog)
are still representable after the update.
The bug would shop up on line 1056, when `offset_1 > current + 1`, which
causes an underflow. This in turn, would cause a segfault on line 1063.
The input must necessarily be longer than 1 GB for this issue to occur.
Even then, it only occurs if one of the last 3 matches is larger than
the chain size and block size.
The zstd reference compressor will not emit a match in the last 7
bytes of a block. The decompressor will also not accept a match
in the last 7 bytes. This patch makes the decompressor accept a
match in the last 7 bytes.
* upstream/dev:
added doc\zstd_manual.html
added contrib\gen_html
zstd_compression_format.md moved to doc/
Fix small bug in ZSTD_execSequence()
improved ZSTD_compressBlock_opt_extDict_generic
protect ZSTD_decodeFrameHeader() from invalid usage, as suggested by @spaskob
zstd_opt.h: small improvement in compression ratio
improved dicitonary segment merge
use implicit rules to compile zstd_decompress.c
detect early impossible decompression scenario in legacy decoder v0.5
no repeat mode in legacy v0.5
fixed invalid invocation of dictionary in legacy decoder v0.5
fix edge case
fix command line interpretation
fixed minor corner case
zstd.h: added the Introduction section
fixed clang 3.5 warnings
zstd.h: updated comments
If a dictionary specifies that a symbol has probability zero in its
`matchLength`, `literalLength`, or `offset` FSE table, but the symbol
appears when compressing input, the compressor fails.
Ensure that dictionaries support all `matchLength`, and `literalLength`
codes. They must also support all of the `offset` codes required to
represent every possible offset that can appear in the first block.
`memmove(op, match, sequence.matchLength)` is not the desired behavior.
Overlap is allowed, and handled as if we did `*op++ = *match++`, which
is not how `memmove()` handles overlap.
Only triggered if both of the following conditions are met:
* The match spans extDict & currentPrefixSegment
* `oLitEnd <= oend_w < oLitEnd + length1 < oMatchEnd <= oend`.
These two conditions imply that the block is less than 15 bytes long.
This bug isn't triggered by the streaming API, because it allocates
enough space for the window size + the block size, so there cannot be
a match that is within 8 bytes of the end and overlaps with itself.
It cannot be triggered by the block decompression API because all of
the decompressed data is in the currentPrefixSegment.
Introduced by commit 7158584399
If `weightTotal == 0`, then `BIT_highbit32(weightTotal)` is
undefined behavior in the case that it calls `__builtin_clz()`.
If `tableLog == HUF_TABLELOG_ABSOLUTEMAX` then we will access one
byte beyond the end of the buffer.
Caused by two things:
1. Not checking that `ip` is in range except for the first byte.
2. `ZSTDv0{5,6}_decodeLiteralsBlock()` could return a value larger than `srcSize`.
If `w ==0` on line 153, then `CTable[n].nbBits == tableLog + 1`.
Then `nbPerRank[CTable[n].nbBits]` and `valPerRank[CTable[n].nbBits]`
are stack buffer overflows.
