which properly represents the maximum bit size of compressed literals (11) as defined in the specification.
To be preferred from HUF_TABLELOG_DEFAULT which represents the same value but by accident.
Name selected to keep the same convention as existing width definitions,
MLFSELog, LLFSELog and OffFSELog.
In rare cases, the default huffman depth selector is a bit too harsh,
requiring brutal adaptations to the tree,
resulting is some loss of compression ratio.
This new heuristic avoids the worse cases, favoring compression ratio.
As an example, compression of a specific distribution of 771 literals
is now improved to 441 bytes, from 601 bytes before.
* Async IO decompression:
- Added --[no-]asyncio flag for CLI decompression.
- Replaced dstBuffer in decompression with a pool of write jobs.
- Added an ability to execute write jobs in a separate thread.
- Added an ability to wait (join) on all jobs in a thread pool (queued and running).
Append -z cet-report=error to LDFLAGS if -fcf-protection is enabled by
default in compiler to catch the missing Intel CET marker:
compiling multi-threaded dynamic library 1.5.1
/usr/local/bin/ld: obj/conf_f408b4c825de923ffc88f7f21b6884b1/dynamic/huf_decompress_amd64.o: error: missing IBT and SHSTK properties
collect2: error: ld returned 1 exit status
...
LINK obj/conf_dbc0b41e36c44111bb0bb918e093d7c1/zstd
/usr/local/bin/ld: obj/conf_dbc0b41e36c44111bb0bb918e093d7c1/huf_decompress_amd64.o: error: missing IBT and SHSTK properties
collect2: error: ld returned 1 exit status
Intel Control-flow Enforcement Technology (CET):
https://en.wikipedia.org/wiki/Control-flow_integrity#Intel_Control-flow_Enforcement_Technology
requires that on Linux, all linker input files are marked as CET enabled
in .note.gnu.property section. For high-level language source codes,
.note.gnu.property section is added by compiler with the -fcf-protection
option. For assembly sources, include <cet.h> to add .note.gnu.property
section.
oss-fuzz uncovered a scenario where we're evaluating the cost of litLength = 131072,
which can't be represented in the zstd format, so we accessed 1 beyond LL_bits.
Fix the issue by making it cost 1 bit more than litLength = 131071.
There are still follow ups:
1. This happened because literals_cost[0] = 0, so the optimal parser chose 36 literals
over a match. Should we bound literals_cost[literal] > 0, unless the block truly only
has one literal value?
2. When no matches are found, the cost model isn't updated. In this case no matches were
found for an entire block. So the literals cost model wasn't updated at all. That made
the optimal parser think literals_cost[0] = 0, where it is actually quite high, since
the block was entirely random noise.
Credit to OSS-Fuzz.
This commit makes several changes:
1. It adds modules for the dictionary builder and errors headers.
2. It captures all of the macros that are used to configure these headers.
When the headers are imported as modules and one of these macros is defined
the compiler issues a warning that it needs to be defined on the CLI.
3. It promotes the modulemap file into the root of the lib directory.
Experimentation shows that clang's `-fimplicit-module-maps` will find the
modulemap when placed here, but not when it's put in a subdirectory.
