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osobhandClaude Opus 5.5 735db117a7 build: pure-Rust zlib-rs as the default deflate backend

The core crates (clawhdf5, -agent, -format, -io, -filters, -ann, -accel,
-netcdf4, -cli) now build no C by default: deflate defaults to zlib-rs,
a pure-Rust port of zlib-ng, and zlib-ng becomes the opt-in
`fast-deflate`, which overrides zlib-rs wherever it is enabled. A default
build no longer needs cmake or a C compiler.

Measured on tank, both builds run alternately, three rounds, medians:
zlib-rs is within 6% of zlib-ng on every HDF5 read and write (512x512
deflate-6 chunked write 1.458 vs 1.484 ms; 64 MB compressed read 64.4
vs 65.2 ms), and compressed output is byte-identical. Details in
BENCHMARKS.md, "Deflate backend".

Getting there took two fixes the first measurement exposed:

- zlib-rs needs `std` to detect SIMD at runtime. flate2 enables it via
  its default `runtime_detection`, which `default-features = false` had
  switched off, leaving zlib-rs 3.5x slower on inflate. The `zlib-rs`
  features now enable it.
- Both deflate paths streamed through flate2's 32 KiB read/write
  wrappers. They now hand the codec the whole chunk in one call, into a
  buffer sized up front (~5% on chunked writes). This also fixes a
  silent short read: the streaming reader returned a truncated stream's
  bytes without an error; a truncated chunk is now DecompressionError.
  In clawhdf5-filters, output longer than the stated size is now an
  error rather than silently cut off.

CI: ci-test.sh lints and tests the zlib-ng path, and fails if a
C-building crate (*-sys, cc, cmake) enters a core crate's default
dependency tree. The arm64 job no longer installs cmake.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

2026-09-23 11:05:22 -05:00

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clawhdf5-filters

Filter and compression pipeline for clawhdf5.

Features

DEFLATE compression/decompression
Pure-Rust deflate via zlib-rs (default, zlib-rs feature)
zlib-ng instead, if you want it (fast-deflate feature; C, needs cmake)
Apple Compression framework support (apple-compression feature)

Usage

use clawhdf5_filters::{deflate_compress, deflate_decompress};

let compressed = deflate_compress(&data, 6).unwrap();
// The second argument bounds the output: the expected decompressed size.
let decompressed = deflate_decompress(&compressed, data.len()).unwrap();

License

MIT

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clawhdf5-filters

Features

Usage

License

828 B

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