Even if the discrepancies are at the moment benign, it's probably better to
standardize on using the one true initializer, rather than trying (and failing)
to correctly duplicate its behavior.
Rewrite ZSTD_createCDict_advanced() as a wrapper around
ZSTD_createCDict_advanced2(). Evaluate whether to use DDSS mode *after* fully
resolving cparams. If not, fall back.
Previously, if DDSS was enabled on a CCtx and a dictionary was inserted into
the CCtx, the CCtx MatchState would be filled as a DDSS struct, causing
segfaults etc. This changes the check to use whether the MatchState is marked
as using the DDSS (which is only ever set for CDict MatchStates), rather than
looking at the CCtxParams.
This makes it clear that not only is the feature allowed here, we're actually
using it, as opposed to the CCtxParam field, in which it's enabled, but we may
or may not be using it.
Unintentional integer overflow (OVERFLOW_BEFORE_WIDEN)
overflow_before_widen: Potentially overflowing expression:
cdict->dictContentSize * 6U
with type unsigned int (32 bits, unsigned) is evaluated using 32-bit
arithmetic, and then used in a context that expects an expression of
type U64 (64 bits, unsigned).
Allow compression to use dictionaries with missing symbols in their
entropy tables. We set the FSE repeat mode to check when there are
missing symbols, and set the FSE repeat mode to valid when all symbols
are present.
Note that when not all symbols are present, the heuristics which favor
dictionary tables for lower compression levels won't activate.
Tested by manually creating a dictionary with missing symbols of every
type, and validing that the compressor rejects it before this change,
and accepts it after this change. Also, I ran the `dictionary_loader`
fuzzer for >1 hour of CPU time without running into cases where
compression succeeds, but decompression fails.
Fixes#2174.
Exposed when loading a dictionary < LDM minMatch bytes in MT mode.
Test Plan:
```
CC=clang make -j zstreamtest MOREFLAGS="-O0 -fsanitize=address"
./zstreamtest -vv -i100000000 -t1 --newapi -s7065 -t3925297
```
TODO: Add an explicit test that loads a small dictionary in MT mode
