* Switch to yearless copyright per FB policy
* Fix up SPDX-License-Identifier lines in `contrib/linux-kernel` sources
* Add zstd copyright/license header to the `contrib/linux-kernel` sources
* Update the `tests/test-license.py` to check for yearless copyright
* Improvements to `tests/test-license.py`
* Check `contrib/linux-kernel` in `tests/test-license.py`
Following #2545,
I noticed that one field in `seq_t` is optional,
and only used in combination with prefetching.
(This may have contributed to static analyzer failure to detect correct initialization).
I then wondered if it would be possible to rewrite the code
so that this optional part is handled directly by the prefetching code
rather than delegated as an option into `ZSTD_decodeSequence()`.
This resulted into this refactoring exercise
where the prefetching responsibility is better isolated into its own function
and `ZSTD_decodeSequence()` is streamlined to contain strictly Sequence decoding operations.
Incidently, due to better code locality,
it reduces the need to send information around,
leading to simplified interface, and smaller state structures.
* Move `counting` to a struct in `FSE_decompress_wksp_body()`
* Fix error code in `FSE_decompress_wksp_body()`
* Rename a variable in `HUF_ReadDTableX2_Workspace`
The most common information that you want to track between begin() and
end() is the timestamp of the begin function, so you can measure the
duration of the (de)compression call. Allow the tracing library to put
this information inside the `ZSTD_TraceCtx`, so it doesn't need to keep
a global map in this case. If a single uint64_t is not enough, the
tracing library can return a unique identifier (like the context
pointer) instead, and use it as a key in a map.
This keeps the simple case simple.
This clarifies operator precedence, and quiets cppcheck in
the Kernel Test Robot. I think this is a slight bonus to
readability, so I am accepting the suggestion.
The unused function definitions are hidden behind a
`#ifndef ZSTD_NO_UNUSED_FUNCTIONS` check.
Initially hiding all functions which are unused and take up more than
2KB of stack space, because these will show up as warnings in the
Linux Kernel build system.
