The window overflow gate mixed two scalar decisions with C-owned pointer and
window state. The early correction test uses the block-start index and must
wait for dictionary invalidation, while the normal fallback uses the block-end
index and the platform-selected ZSTD_CURRENT_MAX threshold. Keeping those
subtractions and the ZSTD_window_t wrapper in C preserves the existing call
contract without making Rust depend on pointer width or private state.
Move the U32 cycle/MAX arithmetic, correction-count scaling, dictionary gate,
and frequent-policy decision into Rust. C passes the two pointer-derived
indices only through scalar results, and supplies the current-max threshold
and active build policy explicitly so 32/64-bit and fuzzing configurations
remain authoritative.
Test Plan:
- `cargo test --manifest-path rust/Cargo.toml --no-default-features
--features compression` -- 348 passed.
- Compression clippy for the library, benches, and tests, followed by
nightly fmt and the repeated three clippy checks -- passed.
- `make -C lib -j2 lib-mt` and `make -C lib -j2 lib-nomt` -- passed.
- `make -C tests -j2 fuzzer` and `./tests/fuzzer -s4142 -t63 -i64 -v` --
passed all 64 cases.
- `make -C tests -j2 test-zstream` -- passed 84 deterministic, 5,477 first
randomized, and 6,902 new-API randomized cases; the existing unterminated
string initializer warning remains.
ddidderr
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