## Reproducing C++ numbers
The plot's C++ bars are pinned constants in `bench_plot.rs` (`cpp_baselines()`),
measured by an out-of-tree harness so this crate keeps no C++ source or build
dependency. To re-measure:
1. Dump the exact encoded bytes the Rust benches see:
```bash
ZEROPARSER_CPP_DUMP_DIR=/tmp/zeroparser-cpp-bench/data \
cargo bench --features zeroparser --bench zeroparser_bench_plot
```
This writes one `<label>@<bytes>B.bin` per scenario plus a `scenarios.txt`
manifest (`<label>,<record_bytes>` lines).
2. In a scratch directory outside this repo, drop the bench `.proto` files
alongside a small driver that:
- generates C++ stubs with the same `protoc` as the libprotobuf you link
(`protoc --cpp_out=.`); confirm `protoc --version` matches the library,
since a `protoc` on `PATH` often differs (with Homebrew the matching pair
is under `$(brew --prefix protobuf)/bin`);
- decodes each `<label>@<bytes>B.bin` in a loop into a single **reused**
message (`ParseFromArray()` clears first), walking every field once via
both `Reflection`/`Get*` (apples-to-apples with `prost-reflect` /
Zeroparser) and generated accessors (apples-to-apples with `prost`); for
repeated/map fields the reflection walk reads `FieldSize`, mirroring
prost-reflect's `List`/`Map` `.len()`;
- mirrors `measure_mbps()` in `bench_plot.rs`: 3 trials, each timing enough
50k-record batches to run ~1 s, reporting
`record_bytes * count * iters / 1024² / elapsed` (MiB, not decimal MB);
- prints `<scenario>,cpp_reflect,<MB/s>` / `<scenario>,cpp_typed,<MB/s>`.
3. Average a few runs and update `cpp_baselines()` in `bench_plot.rs`, keyed
`"<label>@<bytes>B"`, then re-run the bench.
Link the driver against libprotobuf and its abseil dependency (protobuf ≥ 22
needs abseil). With Homebrew on Apple Silicon and no `pkg-config`:
```bash
clang++ -std=c++17 -O3 -DNDEBUG \
-I"$(brew --prefix protobuf)/include" -I"$(brew --prefix abseil)/include" \
driver.cpp *.pb.cc \
-L"$(brew --prefix protobuf)/lib" -lprotobuf -lutf8_range -lutf8_validity \
"$(brew --prefix abseil)"/lib/libabsl_*.dylib \
-Wl,-dead_strip_dylibs -o driver # dead-strip drops unused absl libs
```
