If build_dir is set the zstd build complains about md5sum not being found.
Fix this by checking if build_dir is set before checking and using the hash tool
just like in lib/Makefile .
* 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`
That was a subtle one :
VPATH is affecting search for both %.c source and %.o object files.
This meant that, when an object file already exists in lib/,
it's used in programs/,
even though programs/ is supposed to generate its own %.o object files.
With the new vpath directive, this is no longer the case :
the search is only activated for %.c source files.
Now, local programs/%.o are always generated
even if equivalent ones are already created in lib/.
It more clearly guarantees that lib/ and programs/ can use different compilation directives
without mixing resulting %.o object files.
Building the zstd CLI costs time.
Some part of it is incompressible, leading to substantial iteration delay when testing code modifications.
That's mainly because all source files from the library must be rebuilt from source every time.
The main reason we don't build the CLI from library object files
is that we can't just build the object directly in the lib/ directory
(which they would by default)
since they use different compilation flags.
Specifically, the CLI enables multithreading, while the library doesn't (by default).
This is solved in this commit, by generating the object files locally.
Now, the CLI and the library can employ different sets of flags, without tripping over each other.
All library object files are generated directly into programs/ dir.
This works because no 2 source files have the same name.
Now, modifying a file doesn't require to recompile the entire lib, just the modified files.
The recipe is also compatible with `-j` parallel build, leading to large build time reductions on multi-core systems.
* All copyright lines now have -2020 instead of -present
* All copyright lines include "Facebook, Inc"
* All licenses are now standardized
The copyright in `threading.{h,c}` is not changed because it comes from
zstdmt.
The copyright and license of `divsufsort.{h,c}` is not changed.
benchfn used to rely on mem.h, and util,
which in turn relied on platform.h.
Using benchfn outside of zstd required to bring all these dependencies.
Now, dependency is reduced to timefn only.
This required to create a separate timefn from util,
and rewrite benchfn and timefn to no longer need mem.h.
Separating timefn from util has a wide effect accross the code base,
as usage of time functions is widespread.
A lot of build scripts had to be updated to also include timefn.
When multiple -arch flags are used, the compiler invokes itself once for
each architecture. Apparently, input on stdin is consumed by the
compilation of the first arch and is no longer available to the
compilation of the second arch, which results in a build failure and the
potentially incorrect determination that a feature is not available. So
write the feature detection source to a file instead of using stdin.
