Files

T

Move FSE normalized-count parsing, Huffman statistics decoding, FSE table
construction, and FSE stream decompression into Rust. The C source files now
only retain the headers needed by the existing build configuration.

The implementation keeps the public C ABI and verifies C-generated balanced,
skewed, and Huffman-statistics streams. Compression and the higher-level frame
decoder remain C for now.

Test Plan:
- cargo fmt --check
- cargo test --all-targets
- cargo clippy --all-targets -- -D warnings
- cargo build --release
- compile both C shims with -Werror and -Wredundant-decls

Refs: rust/README.md

2026-07-10 20:04:26 +02:00

src

feat(rust): port FSE entropy decoding

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Cargo.lock

feat(rust): add common primitive compatibility layer

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Cargo.toml

feat(rust): add common primitive compatibility layer

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README.md

feat(rust): port FSE entropy decoding

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README.md

Rust rewrite

This directory contains the in-progress Rust replacement for the zstd library and command-line program. During the migration, the crate is built as a static library and linked into the original C test programs. Production C translation units become declaration-only shims as their implementations move to Rust; the original C tests remain unchanged and provide compatibility coverage.

Component map

The crate is organized from low-level representation helpers toward the public zstd ABI:

Common primitives
- mem, bits, bitstream, and cpu implement byte-order, bitstream, and target-feature operations used by the codecs.
- errors, debug, xxhash, and zstd_common provide common exported ABI functions and state.
- common contains shared frame constants and internal data types.
Entropy coding
- entropy_common reads FSE normalized counts and Huffman statistics.
- fse_decompress builds FSE decoding tables and decodes FSE streams.

The remaining compression, general decompression, dictionary, legacy, runtime, and CLI translation units are still C. They must move before the rewrite is complete. Keeping that boundary explicit prevents a passing hybrid build from being mistaken for the final all-Rust result.

Compatibility boundary

The public ABI continues to come from the existing headers under lib/. Exported Rust functions therefore use C layout and calling conventions. A C source file whose implementation has moved to Rust remains in the original makefile source list as a small shim so header configuration and platform preprocessor behavior stay available during the transition.

The original test makefile links target/release/libzstd_rs.a with whole-archive semantics. Rebuild the Rust archive before running C tests so the executable does not use a stale implementation.

Validation

Run focused Rust checks from this directory:

cargo fmt --check
cargo clippy --all-targets -- -D warnings
cargo test --all-targets
cargo build --release

Then run original compatibility tests from the repository root, starting with the narrow target for the component being migrated. For example:

make -C tests fuzzer
./tests/fuzzer -i1 --no-big-tests

Broader tests/Makefile targets remain the authoritative integration gates as more of the library and CLI are rewritten.