FA-72215 / Error-correcting codes / Member archive

LT peeling copies the symbol value without removing resolved neighbours · case 05

Resolved source values are wrong whenever the releasing symbol had degree above one.

Member previewVariant 5 · 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, 1, 2], 12], [[2], 186], [[0, 2], 237]], 3]	`[237, 12, 186]`	`[87, 225, 186]`	Failed

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