Crate seyd_fec 

Reed-Solomon erasure coding over GF(256) with a Cauchy generator matrix.

Rationale, measurements and history live in PLAN.md §1.7 and in the legacy Python reference packages/agent/fec.py. What matters for this crate:

• k parity chunks over n equal-length data chunks recover any k erasures. Cauchy rather than Vandermonde because every square submatrix of a Cauchy matrix is invertible, which is exactly that guarantee.
• The construction — poly 0x11d, A[i][j] = 1 / (i XOR (k + j)) — is part of the wire contract. Changing it breaks interop silently, which is why tools/fec-vectors.py | cargo run -p seyd-fec --example check exists.
• The coder is payload-agnostic: it never parses what it protects.

Modules

gf

GF(256) arithmetic, field polynomial 0x11d.

Constants

MAX_SYMBOLS

Hard limit of the construction: n + k <= 256.

Functions

cauchy_matrix

decode

Reconstruct missing data chunks in place. Returns false if unrecoverable.

encode_parity

Compute k parity chunks from n equal-length data chunks.

parity_count

Parity chunks for an n-chunk block at pct overhead.

Type Aliases

Matrix

k x n Cauchy matrix, cached per (n, k).