gamut-dsp

gamut-dsp holds the shared digital signal processing routines for the gamut codecs — the transforms, quantization, and filtering the format crates call into.

Goals

Part of the gamut workspace, this crate exists to:

Keep the math in one place. Transforms and related DSP are implemented and tested once here, rather than re-derived inside each codec, so a numerical bug is fixed for every format at once.
Track the spec exactly. Routines are implemented clean-slate from the official specs (see ../../references/) — the M0 pair is the AV1 lossless 4×4 Walsh–Hadamard transform ([fwht4x4] / [iwht4x4]), the exact inverse the AV1 decoder expects.
Stay allocation-conscious. The transforms operate on fixed-size [i32; 16] arrays with no heap allocation in the hot path.
Stay memory-safe. #![forbid(unsafe_code)].

Usage

use gamut_dsp::{fwht4x4, iwht4x4};

// The forward/inverse 4x4 Walsh-Hadamard transform round-trips exactly (lossless).
let residual = [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
let coeffs = fwht4x4(&residual);
let restored = iwht4x4(&coeffs);
assert_eq!(residual, restored);

Status

M0 provides the lossless 4×4 Walsh–Hadamard transform pair used by AV1 lossless intra coding. The discrete cosine / asymmetric discrete sine transforms used by lossy AV1 coding (AV1 §7.13.2.2–.9), plus quantization and in-loop filtering, are deferred to milestone M1 (see gamut-avif/STATUS.md).

Roadmap

M1: lossy DCT/ADST transform family and quantization.
Later: filtering primitives and (where it pays off) SIMD-optimized variants.

License