Zstandard / zstd (vendored into calog)
======================================

Zstandard (zstd), the fast real-time compression library by Meta Platforms
(https://github.com/facebook/zstd). calog builds it from source into
lib/libzstd.a as the zstd backend for the archive/compression library
(libarchive's zstd filter) and as a single, reproducible source of truth for
zstd across the whole build.

Vendored from zstd 1.5.6: only the buildable library subset, i.e. the .c/.h
files under lib/common, lib/compress and lib/decompress plus the public headers
lib/zstd.h and lib/zstd_errors.h. Preserves the common/compress/decompress
directory layout because the internal sources include "../zstd.h" and sibling
headers by relative path. libarchive needs zstd.h, found via -Ivendor/zstd.

Trimmed from the upstream tree: the CLI (programs/), tests, docs, examples,
contrib, the dictionary builder (lib/dictBuilder + zdict.h), the deprecated and
legacy format shims (lib/deprecated, lib/legacy), the DLL glue (lib/dll), and
all build scaffolding (Makefile, *.mk, *.pc.in, BUCK, module.modulemap).

Also removed: lib/decompress/huf_decompress_amd64.S (an x86-64-only assembly
fast path). calog compiles the portable C path instead by defining
ZSTD_DISABLE_ASM, so the object rules stay pure .c and portable to every target.

Single-threaded on purpose: ZSTD_MULTITHREAD is left UNDEFINED (zstd tests it
with #ifdef, so it must never be defined -- not even to 0), which keeps the
encoder single-threaded and calog's actor model and tsan targets clean. The
multithread source (lib/compress/zstdmt_compress.c) and the thread-pool shims
(lib/common/pool.c, lib/common/threading.c) are still vendored because the
build references them; with ZSTD_MULTITHREAD unset they compile to their
single-threaded no-op fallbacks.

No configure step is needed. License: BSD 3-Clause (zstd is dual-licensed
BSD-3 / GPLv2; calog uses the permissive BSD-3 option). See LICENSE.