FA-72219 / Error-correcting codes / Member archive

LT peeling releases only original degree-one symbols · case 04

Higher-degree symbols are never peeled, leaving many sources unresolved.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Peeling (belief-propagation) decoder for an LT fountain code over bytes. symbols is a list of [neighbour indices, XOR of those source symbols]. Repeatedly find an encoded symbol with exactly one unresolved neighbour, resolve it as the value XOR all resolved neighbours, and continue until a full pass makes no progress. Return the k source values with None for unresolved ones.

Why this case matters

Broadcast and storage systems use fountain codes; peeling must continue as long as new degree-one symbols appear.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression [[[[0, 4], 212], [[0], 114], [[0, 4], 212], [[0, 1, 4], 93], [[0], ...	`[114, null, null, null, null]`	`[114, 137, null, null, 166]`	Failed

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