SoA implementation for float and AVX2 includind the polyexp fix

2026-05-25 12:07:46 +02:00
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+# Optimization: SoA (float version)
+
+- **Author**: Linus
+- **Predecessor**: variant_float_inlining.cpp
+- **File(s)**: variants/variant_float_inlining_SoA.cpp
+- **Status**: TBD
+
+## What this changes
+
+Same SoA layout switch as the double `variant_inlining_7_SoA`, but starting
+from the float baseline instead of the double one. `Pedestrian` struct is
+replaced by file-scope `vector<float>` arrays (`pos_x`, `pos_y`, `sb_e_x`,
+`sb_e_y`, `sb_sq`, `e_x`, `e_y`, `w_x`, `w_y`, `curr_vel_x`, `curr_vel_y`,
+`desired_v0`, `v_max`, `destination_x`, `destination_y`, `color`). Board
+obstacles stay AoS.
+
+Mostly a setup step for the float AVX2 variant. Same reasoning as the
+double SoA: gets the j-side loads contiguous so the upcoming 8-wide AVX2
+loop has clean aligned chunks.
+
+The j loop also keeps the `r_ab_norm > EPS ? : EPS` and `two_b_sq > EPS_SQ
+? : EPS_SQ` clamps from the float baseline. Float precision around close
+encounters can collapse those to zero where double would not, and the clamp
+keeps the division finite.
+
+## Code (relevant snippet)
+
+
+See `variants/variant_float_inlining_SoA.cpp`.
+
+## Benchmark
+
+Conditions: min of N runs (TBD), N_ITER=1000, -O3 -march=native -flto.
+Diff is vs `variant_float_inlining`.
+
+### x86
+
+**Machine**: TBD
+
+**Frequency**: TBD
+
+| N    | W(n) [Flops] | T(n) [Cycles] | Performance [Flops/Cycle] | Diff vs Predecessor |
+| ---- | ------------ | ------------- | ------------------------- | ------------------- |
+| 50   |              |               |                           |                     |
+| 100  |              |               |                           |                     |
+| 200  |              |               |                           |                     |
+| 500  |              |               |                           |                     |
+
+### ARM (Apple)
+
+**Machine**: TBD
+
+**Frequency**: TBD
+
+| N    | W(n) [Flops] | T(n) [Cycles] | Performance [Flops/Cycle] | Diff vs Predecessor |
+| ---- | ------------ | ------------- | ------------------------- | ------------------- |
+| 50   |              |               |                           |                     |
+| 100  |              |               |                           |                     |
+| 200  |              |               |                           |                     |
+| 500  |              |               |                           |                     |
+
+## Analysis
+
+Layout change only, so the expectation is roughly no win on its own. The
+float scalar loop already auto-vectorises in pieces with `-O3
+-march=native`, so SoA doesnt buy much over what the AoS version was
+already doing. The real payoff lands in the AVX2 child.
+
+Verify passes against `baseline_float_n60_i500.csv` (from
+`variant_float_baseline`) at the 1cm tolerance.
+
+## Takeaway
+
+Setup step for the AVX2 variant.