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.
Yann Collet
Yann Collet
ko-zu
W. Felix Handte
Nick Terrell
Jennifer Liu
modbw
Jennifer Liu
cyan4973
Nick Terrell
Duc Ngo
Ryan Schmidt
George Lu
fbrosson
Baruch Siach
Peter Seiderer
taigacon
Björn Ketelaars
René Rebe