# CLAUDE.md
## Project overview
This is `tdigest`, a Rust implementation of the t-digest data structure for accurate quantile estimation. It follows Facebook's folly TDigest implementation. The crate is published on crates.io as `tdigest`.
## Build and test commands
```bash
cargo build # Build with default features
cargo build --all-features # Build with serde support
cargo test --all-features # Run all tests including serde round-trip
cargo test --features serde # Test the preferred serde feature
cargo test --features use_serde # Test the compatibility alias
cargo fmt --all -- --check # Check formatting
cargo check --all-features # Type-check only
cargo check --no-default-features # Verify no_std + alloc
```
## Project structure
- `src/lib.rs` -- entire library: `Centroid`, `TDigest`, all methods, and all tests
- `Cargo.toml` -- package metadata, MSRV 1.62, default `std`, optional `serde`, and compatibility `use_serde` features
- `docs/architecture.md` -- algorithm and architecture documentation
- `rustfmt.toml` -- max_width = 120
## Code conventions
- Single-file library (`src/lib.rs`), tests are inline `#[cfg(test)]` at the bottom
- Immutable API: data methods (`merge_sorted`, `merge_unsorted`) take `&self` and return a new `TDigest`
- `Option<f64>` for fallible queries (`min`, `max`, `mean`, `estimate_quantile`) -- never NaN sentinels
- `#[must_use]` on methods returning new values
- `#[non_exhaustive]` on public structs
- `debug_assert` for invariant checks (NaN rejection, min/max presence)
- No external dependencies by default; serde is behind the `serde` feature, with `use_serde` as a deprecated alias
- The library is `no_std` and uses `alloc`; the default `std` feature preserves existing behavior
- Formatting: rustfmt with max_width=120
## CI
GitHub Actions (`.github/workflows/CI.yml`): check, test (ubuntu/macos/windows), MSRV (1.62), no_std, clippy, rustdoc warnings, semver checks, code coverage (tarpaulin + codecov), and rustfmt. Fuzzing is a separate manual workflow.