Fr0zkaandClaude Opus 5.5
c0c204ba50
VoxelHash::Cell/Pair, legacy Cellular3D and the shared Core cellular hash added 0x7FFFFFFF to a signed int32 before casting to uint32; overflow is undefined, so Clang and GCC placed cave passage 1 differently (first differing sample at LOD1 tile (0,64,-512)). The bias is now done in unsigned arithmetic, in both the standalone copy and the Unreal plugin header (Source/VoxelForge/Public/VoxelCaveMorphology.h). Native caves, motifs and lattice now stream LOD0-8 with skirts and cross-level transitions. New verify.py --speed-matrix runs every generator on one asserted-identical view (5 interleaved runs): motifs 1.33, profiles 1.30-1.32, caves 1.41, natural SW 1.67, lattice 1.70, FI 4.93 s whole view. fast/medium/full PASS, Clang/GCC peer hashes equal. Research R29 (open-edge ledge) and R30 (compiler-divergence suspects). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1
78 lines
6.7 KiB
Markdown
78 lines
6.7 KiB
Markdown
# Linux 60 report
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## Result and root cause
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The continuation is green. The full tier and speed matrix passed after fixing signed-overflow undefined behavior in the shared voxel hash.
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The first differing density was LOD1 tile `(0,64,-512)`, step 2, sample order 23,658 at `(64,82,-476)`. Before the fix, Clang returned `-4.0078125` (`0xc0804000`) and GCC returned `-4.125` (`0xc0840000`). The sample follows the mesher's LOD X8/boundary scalar path into `DensityAtLattice` and the compiled analytic `TunnelNetwork` field. Its upstream cave passage placement comes from `UVoxelStrateManager::GeneratePassages` → `PassageRandom01` → `VoxelHash::Cell(i,c,seed)`.
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`VoxelHash::Cell` added `0x7fffffff` to a signed cell coordinate before casting to `uint32`; connection `c=1` overflowed `int32`, so the compiler-dependent hash changed the passage coordinates and cave geometry. The trace showed passage pair `(0,1)` diverging, followed by all 21 control points of passage 1. The fix performs the bias in unsigned arithmetic in `Cell`, `Pair`, legacy `Cellular3D`, and the shared Core cellular hash. It does not quantize density. After the fix both compilers produced the same pair `(0,1)` coordinates, the same 44 passage points, and `0xc0804000` at the first sample. The evaluator version is now 211.
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Before/after traces are in `Saved/Linux/l60/diag/caves-{clang,gcc}-probe.log` and `Saved/Linux/l60/diag/cache/fullcache-{clang,gcc}.log`.
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## Far LOD support and seam checks
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All full-view fixtures use max level `-1`, clip radius 3, and max clip level 8. All three generators streamed LOD0–8 with skirts.
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- **Caves:** X8 and Z-run gates detect caves in manager and resolved stratum mappings, then use scalar lattice sampling for cave samples. Clang/GCC cave tile hashes match at W1/W8/W12, including random views at LOD1–2. The cave-mouth transition crossed levels 0–8 (432 entering tiles).
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- **Motifs:** The fixed motif field streams through the existing rings, caps, and skirts. The monolith transition crossed levels 0–8 (295 entering tiles); whole-surface foot, cap, and platform-edge audits passed.
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- **Lattice:** The fixture selects native lattice stratum 1 and uses the existing ring and skirt path. The helix transition crossed levels 0–8 (380 entering tiles); field, interval, reachability, and shape-free audits passed.
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Hard, gradient, and interleaved stratum transitions passed with zero hole columns and zero air samples. Far-LOD cave, motif, and lattice JPEG captures passed their audits and are under 300 KB.
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## Comparable speed matrix
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`verify.py full --speed-matrix` ran five interleaved repetitions per generator, rotating generator order. Every run used camera `(-12,-118,-20 m)`, rotation `(0°,0°)`, clip radius 3, max clip level 8, max level `-1`, camera step 24 m, 12 workers, and shared column cache. The stage asserted the shared HeadlessConfig fields, whole-view and per-LOD tile-count ranges, and stable counts across repetitions. It passed for all eight generators. Every listed tile count occurred in all five runs; timings are medians from the final full run.
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| Generator | Tiles | Whole view (s) | First tile (s) | Near ring (s) | Moving p50 (ms) | Moving p95 (ms) |
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|---|---:|---:|---:|---:|---:|---:|
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| Natural SW | 2,130 | 1.669 | 0.502 | 0.519 | 63.971 | 119.891 |
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| periodicHills | 1,986 | 1.311 | 0.454 | 0.479 | 60.267 | 115.648 |
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| mirroredRelief | 1,986 | 1.317 | 0.471 | 0.490 | 60.568 | 115.474 |
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| flatField | 1,986 | 1.303 | 0.465 | 0.485 | 60.627 | 117.144 |
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| Floating Islands | 2,130 | 4.926 | 0.817 | 0.977 | 528.939 | 871.290 |
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| Caves | 2,130 | 1.408 | 0.489 | 0.507 | 61.099 | 118.508 |
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| Motifs | 1,986 | 1.326 | 0.476 | 0.493 | 60.107 | 116.104 |
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| Lattice | 2,130 | 1.701 | 0.539 | 0.561 | 69.572 | 137.585 |
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Full run records and common config are in `Saved/Linux/l60/speed-matrix.json`.
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## Captures
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- `Saved/Linux/l60/captures/caves-far-lod.jpg` — 16,642 bytes; SHA-256 `55f8d3d2de76541e9f1c1d09b771af40bfbb37b1ce5afc0b2f70419b84ed71a3`
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- `Saved/Linux/l60/captures/motifs-far-lod.jpg` — 24,926 bytes; SHA-256 `bfc5d8ddebc3706fedd6108653b4777fac4bac44e71f60c8e58b3508c14c3aa6`
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- `Saved/Linux/l60/captures/lattice-far-lod.jpg` — 30,714 bytes; SHA-256 `c261728e48975f01c712e31594b4284eede289b73e793e6204b78cb8ff2a2947`
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## Hashes and tiers
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Clang 19 and GCC 14 builds used FP contraction off and 12 jobs. Final source stamp and source-manifest SHA-256: `902a0d8e45f895d1b53c0a86999adee5598ff77e1752aa7ea90397520cf7b82d`.
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- Clang headless: `dcf6286bcecac382f9cce2458e7c327485e9b8b993c3d544e627a8fc964947fa`
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- GCC headless: `be86f90f993ba27bfde235e0850ea783298396dc03456360cf4bb3fd4815988b`
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- Offscreen capture: `b8f7a441c0a41be6ebd61721ff903832a51291df7a886e669b9084d84441d4c5`
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| Tier | Status | Checks / runs | Elapsed |
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|---|---|---:|---:|
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| Fast | PASS before hash fix | 453 / 113 | 335.7 s |
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| Medium | PASS before hash fix | 968 / 289 | 1,559.1 s |
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| Full continuation trial 1 | FAIL: stale binary stamp; no checks ran | — | 0.0 s |
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| Full continuation trial 2 | PASS on source stamp `914af3...` | 2,304 / 660 | 3,256.9 s |
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| Full continuation trial 3 | PASS on final source stamp, including speed matrix | 2,304 / 660 | 3,260.6 s |
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Fast and medium were not rerun as standalone tiers after the hash change; the passing full run executed their checks at the current source stamp.
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## Trials and failed runs
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The prior L60 work used 15 trials. This continuation used 3 of its 10-trial budget. Trial 1 stopped before checks because it found stale Clang/GCC executables. Trial 2 passed, then the final source review restored the mesher's existing `<bit>` include and changed the source stamp, so trial 3 rebuilt and reran full against the exact final source. The pre-fix trial 15 had failed peer determinism on the same six LOD1 and eight LOD2 tile keys across four seeded views. Trial 3 had no failed checks; negative controls reported expected failures.
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## Orchestrator review (Claude)
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Accepted. The stamp matches the final Clang and GCC builds (`902a0d8e…`); full PASS, including the speed matrix.
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**The root cause is a real cross-platform determinism bug:** `VoxelHash::Cell`/`Pair`/`Cellular3D` added
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`0x7FFFFFFF` to a signed `int32` (signed overflow is undefined behaviour), so passage placement became
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compiler-dependent. **The same code lives in the Unreal plugin** (`Source/VoxelForge/Public/VoxelCaveMorphology.h`,
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identical to the standalone copy before the fix), and only the standalone copy had been fixed. I applied the identical
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fix to the plugin header and confirmed the two copies match. MSVC typically wraps there, so the owner's existing
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worlds are most likely unchanged, but this needs his Windows build. No other signed-bias pattern remains in `Source/`
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or Core. The comparable speed matrix is now a standing `verify.py full --speed-matrix` stage.
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