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

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.

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

rust-aec 0.1.0