The window-overflow helper mixed pointer arithmetic and ZSTD_window_t state
updates with the scalar U32 cycle calculation that determines the correction.
That made the arithmetic boundary depend on the host pointer implementation.
Add a narrow Rust ABI leaf that accepts only the current index, cycle log, and
maximum distance. Rust preserves the start-index adjustment, cycle alignment,
cycle-size versus max-distance selection, and explicit U32 wrapping. C derives
newCurrent from the returned correction so it can retain every invariant check,
pointer update, workspace/table transition, counter update, and dictionary
invalidation in the existing stateful wrapper.
Test Plan:
- Rust compression clippy, bench clippy, test clippy, nightly fmt, and the
repeated three clippy checks -- passed.
- `cargo test --manifest-path rust/Cargo.toml --no-default-features
--features compression` -- 340 passed.
- `make -C lib -j2 lib-mt` and `make -C lib -j2 lib-nomt` -- passed.
- `./tests/fuzzer -s4142 -t63 -i64 -v` -- focused overflow coverage passed.
- `make -C tests -j2 test-zstream` -- 84 deterministic, 5,018 standard
randomized, and 8,851 new-API randomized cases passed.
- `make -C tests -j2 test-fuzzer` reaches the pre-existing CCtx-reuse test 56
failure; a pristine 837e4f099 worktree reproduces it, while the focused
test-56 run passes.
ddidderr
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