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pepijn
1e2057e3be
Drop the Feistel permutation (and its SplitMix64 hash / cycle-walking) in favor of a torch.randperm seeded from (seed, epoch). The deterministic mode keeps its key properties - data order is a pure function of (seed, epoch), so it reproduces on every rank with no global-RNG synchronization, and - state_dict / load_state_dict still resume sample-exactly, now by regenerating the epoch's permutation and slicing from the saved offset. Construction stays O(num_episodes) (only episode boundaries are stored, never a per-frame index list). The trade-off vs Feistel: the per-epoch shuffle is again O(num_frames) memory (the randperm tensor) and no longer O(1)-seekable, in exchange for ~30 fewer LOC and a truly uniform shuffle. Tests updated: the trillion-frame O(1) test is replaced with a boundary-storage check and a scale resume-exactness test. Co-authored-by: Cursor <cursoragent@cursor.com>