FA-87749 / Collision detection broadphase / Member archive

Hash products are not reduced to 32 bits · case 04

Negative cells map to different buckets than the native engine.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

solve(frames, n): particle hash table of n buckets reused across frames without clearing; a bucket whose stamp is older than the frame is lazily reset on first insert. Cell = floor(x), floor(y); bucket = ((ix*73856093 mod 2^32) xor (iy*19349663 mod 2^32)) mod n. A particle pairs with earlier particles in the same bucket only if they share the exact cell. Per frame return [sorted [min,max] pairs, buckets stamped this frame].

Why this case matters

Broadphase stages decide which object pairs ever reach narrowphase; a wrong boundary, ordering or bookkeeping rule silently drops real contacts or floods the solver with false candidates.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
case 0	`[[[], 3], [[[4, 17]], 2], [[], 3]]`	`[[[], 2], [[[4, 17]], 2], [[], 2]]`	Failed

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