rust-aec

Pure Rust decoder for CCSDS 121.0-B-3 Adaptive Entropy Coding (AEC), with an initial focus on GRIB2 Data Representation Template 5.0 = 42 (CCSDS/AEC).

This crate was created to avoid native libaec build friction (C/CMake/bindgen) on Windows while keeping byte-for-byte compatibility.

Repository: https://github.com/hkwk/rust-aec

Documentation (English): docs/README.md

See CHANGELOG.md for recent changes and release notes.

Visual comparison

rust-aec	libaec

Status

• Decoder implemented for the subset needed by GRIB2 template 5.0=42.
• Validated against libaec using an “oracle” byte-for-byte comparison on real GRIB2 data (in the upstream workspace that hosts this crate).

What this crate provides

• decode(input, params, output_samples) -> Result<Vec<u8>, AecError>: decode an AEC bitstream into packed sample bytes.
• AecParams / AecFlags: minimal parameter set aligned with libaec’s aec_stream.
• flags_from_grib2_ccsds_flags(ccsds_flags: u8): helper for GRIB2 template 5.42.

Non-goals (for now)

• Full coverage of every possible libaec flag combination.
• Streaming / incremental decode API.
• Complete GRIB2 decoding pipeline (bitmap/reduced grids etc.). This crate only decodes the AEC payload.

Usage

Decode a GRIB2 template 42 payload

You need:

• payload: the GRIB2 Section 7 payload (the CCSDS/AEC bitstream)
• num_points: number of decoded samples (GRIB2: section5.num_encoded_points)
• bits_per_sample, block_size, rsi, ccsds_flags: from GRIB2 template 5.42

use rust_aec::{decode, flags_from_grib2_ccsds_flags, AecParams};

let params = AecParams::new(
    12,                 // bits_per_sample
    32,                 // block_size
    128,                // rsi
    flags_from_grib2_ccsds_flags(0x0e),
);

let decoded: Vec<u8> = decode(&payload, params, num_points)?;

decoded is a byte vector of length num_points * bytes_per_sample, where bytes_per_sample = ceil(bits_per_sample/8). Byte order is controlled by the MSB flag.

Example program

This crate ships a small example binary:

cargo run -p rust-aec --example decode_aec_payload -- --payload aec_payload.bin --samples 1038240

API notes

• When AecFlags::DATA_PREPROCESS is set, the output bytes are the reconstructed sample values (inverse preprocessing applied).
• When preprocessing is not set, the output bytes represent the raw coded values.

License

MIT. See LICENSE.

Related

• The host workspace includes a GRIB2 preview integration that can fall back to rust-aec for template 42.

Vendored reference code

This repository may contain vendored third-party sources under vendor/ (e.g. libaec-sys/libaec) for local reference and oracle comparisons.

• These vendored directories are excluded from crates.io packages via Cargo.toml exclude.
• rust-aec itself remains a pure Rust implementation.