# Linux76 report: legacy FI/TN sample cost

## Per-term profile

The term profiler sampled 1 in 256 density points and scaled timed calls by their observed counts. Worker-ms are summed across LODs; ns/sample divides by legacy FI/TN field evaluations. These are sampled estimates, not wall time. Before is L75; after is the final constants-only source.

| Term | FI worker-ms / ns per sample, before → after | TN worker-ms / ns per sample, before → after |
|---|---:|---:|
| Primitive scan | 1,116 / 186 → 1,133 / 189 | 997 / 179 → 1,037 / 186 |
| DetailNoise call (pre-noise fade excluded) | 38 / 6.4 → 39 / 6.5 | 63 / 11.3 → 68 / 12.2 |
| ↳ Surface relief noise, inside detail | 7.6 / 1.3 → 7.7 / 1.3 | 12.3 / 2.2 → 13.2 / 2.4 |
| ↳ Owner noise and warp, inside detail | 26.2 / 4.4 → 26.9 / 4.5 | 43.2 / 7.8 → 46.7 / 8.4 |
| Composer cavern | 142 / 23.6 → 145 / 24.1 | 122 / 21.8 → 127 / 22.8 |
| Composer boundary band | 338 / 56.3 → 350 / 58.2 | 306 / 55.0 → 321 / 57.8 |
| Composer passage/support | 6,462 / 1,076 → 6,323 / 1,053 | 5,475 / 984 → 5,522 / 993 |
| Composer stamps | 0 / 0 → 0 / 0 | 0 / 0 → 0 / 0 |
| Edit brushes | 133 / 22.1 → 135 / 22.5 | 114 / 20.5 → 119 / 21.3 |
| Smooth-min across legacy evaluation | 166 / 27.6 → 170 / 28.3 | 143 / 25.6 → 151 / 27.2 |

FI used 6,005,989 legacy samples and TN 5,562,334. The primitive bins supplied 2.75 FI / 3.85 TN candidate references per sample; only 0.251 / 0.237 per sample reached primitive-distance evaluation. The code scans references in the selected 3D bin, not the full primitive set. Smooth-min ran about 1.27 times per legacy sample and overlaps the primitive/composer rows; do not add it again. The noise subrows are inside `DetailNoise`. Its timer excludes the preceding fade and layer lookup. Surface relief evaluates 3D value-noise wavelengths 32, 16, and 4; noise timers cover helper calls, not individual octave loops.

Passage/support dominates: about 1.05–1.08 μs per sample versus 0.18–0.19 μs for primitive scan. Per-tile filtering of the upper-mouth scan matched hashes but regressed TN by 5.43% in the first whole-view timing set, so it was removed. Broad per-tile passage-loop filtering failed hashes and was rejected. The remaining relief-call counter includes path-relief calls and does not establish repeated triplets for the same sample; no sample cache was shipped.

The profiler adds about 1.9% on FI and 2.1% on TN by the median of three paired W8 runs against the same clean build. Pair deltas were FI +1.90%, −3.33%, +2.19%; TN +2.10%, +7.00%, −1.91%. This spread is visible instrumentation cost, not field speedup. Profile inputs and summaries are in `Saved/Linux/l76/term-profile-before/`, `term-profile-constants-only/`, and `term-profiler-overhead-constants-only/`.

## Invariants and changes

- `StrataDistance(Z)`, layer lookup, and bound-stratum lookup are Z-only. `FloorAt(P,X,Y)` and some projection parameters are XY-only for a fixed primitive/feature, but primitive selection, floor blending, and the resulting composer values still depend on Z.
- Surface and passage relief use 3D noise; owner warps also depend on effective Z. The SW column cache is not reused for these values.
- Cached resolved-passage metadata once at field binding: internal-chain and landing flags, first/last floor Q, lower-mouth index, carve margin, and mouth search limits. Per-sample arithmetic order is unchanged. The profiler is opt-in at build time with `VOXELFORGE_PROFILE_LEGACY_TERMS=1`; timer bodies compile out in default builds.
- The whole-view effect of the constants hoist is mixed and near noise. No FP reordering was made, hashes stayed identical, and no version bump was needed.

## Hashes

Final Clang/GCC candidate per-tile hashes matched the L75 reference for density, mesh, payload, and topology in all 24 compiler × worker × view comparisons (W1/W8/W12, four views). Each compiler/worker set covered 9,661 tiles.

Final Clang/GCC source stamp: `285080616b0c5b65a670a72858e3b7e922b302df183b247c238504d58aa2b82f`.

| View | Tiles | Density | Mesh | Payload | Topology |
|---|---:|---|---|---|---|
| SW | 2,850 | `40b76d0072a2adcd` | `8559df0850d4d7f1` | `7700965ff31ac702` | `0e7f2a16b4cc71a9` |
| FI | 2,249 | `99ca213b21ce86e4` | `2977525405b79fff` | `3d7d2efb581710bd` | `af1916c949224871` |
| TN | 2,233 | `8d23c26f5c092be1` | `15c3aad2e29d9ea0` | `3d48f68d511c21df` | `5b1584676884edd8` |
| VS | 2,329 | `876b44981d106be3` | `aaef57cb08bd6845` | `b19617df9f4acbb1` | `e8eee991260adff4` |

The rows above are the matching W8 Clang whole-view hashes; GCC and the other worker counts matched each corresponding L75 tile hash as well. Per-tile comparison summary: `Saved/Linux/l76/hashes/final-clean/summary.json`.

## Whole-view timing

Three interleaved W8 pairs per view; seconds are `(L75 → L76)` in pair order. The delta is the median of paired percentage changes.

| View | Pair times | Median paired delta |
|---|---|---:|
| SW | 2.428→2.404, 2.499→2.456, 2.343→2.347 | −0.024 s (−0.99%) |
| FI | 4.505→4.668, 4.778→4.635, 4.414→4.413 | −0.001 s (−0.02%) |
| TN | 4.389→4.289, 4.132→4.408, 4.417→4.337 | −0.080 s (−1.81%) |
| VS | 2.454→2.489, 2.353→2.426, 2.365→2.461 | +0.073 s (+3.10%) |

The largest median paired change is +0.073 s (VS); the best is −0.080 s (TN). Whole views remain 2.4–4.6 s, far from the ~1 s goal. Passage/support remains the next cost target.

Timing rows and logs are in `Saved/Linux/l76/timing-constants-only/summary.json`.

## Audits and builds

- Final `verify.py fast`: PASS in 381.8 s; passage audits, fast-tier hash gates, and controls completed.
- Final fast-tier summary: `Saved/Linux/l76/verify/fast-summary.json`.
- Linux UE host `VFHostEditor Linux Development`: succeeded in 121.98 s with `taskset -c 0-11`, `-MaxParallelActions=4`, and no address-space limit. Three existing RealtimeMesh deprecation warnings were emitted. Log: `Saved/Linux/l76/ue-build.log`.
- All headless runs used `taskset -c 0-11` and `prlimit --as=6442450944`; no run exceeded 30 minutes.

## Failed runs

- Broad per-tile passage-loop filtering failed Clang W1 SW hashes: 612 density mismatches and 24 each in mesh, payload, and topology. It was removed.
- The first fast-tier launch stopped before tests because its output-directory executable had not been built. After building the requested binaries, the final fast tier passed.
- The first UE invocation used a nonexistent direct `Engine/Binaries/DotNET/dotnet` path. The engine `Build.sh` wrapper set up bundled DotNet and the host build succeeded.

No commit, push, or stash was made.