FA-86509 / Procedural level generation constraints / Member archive

Chunk seed derivation: Transposed chunks share a seed · case 04

Chunk (3, 5) and (5, 3) generate identical terrain.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Coordinates are zigzag encoded (v >= 0 -> 2v, v < 0 -> -2v-1). seed = (world_seed*1000003 mod 2^32) xor (zz(cx)*73856093 mod 2^32) xor (zz(cy)*19349663 mod 2^32). The generator state is seed, or 1 when seed is 0, advanced by three 32-bit xorshift rounds (<<13, >>17, <<5, each left shift masked to 32 bits). Returns [seed, state % 100].

Why this case matters

Procedural generators silently emit unplayable or unfair levels when a single constraint check uses the wrong boundary, axis, neighborhood or update order; the defect is visible in exact generated geometry.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
mirrored coordinates #1	`[906427993, 47]`	`[294384589, 20]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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