Profiling-driven (sample + disasm comparison vs clang -O3). All changes
safe Rust except one debug_assert-guarded extension of the existing
SyncSlice unsafe contract. Determinism preserved: hash bit-identical
across workers 1/2/4, NEON/SSE2/scalar, internal/external task systems
(new baseline 0x9018E2D8 after approved FMA contraction).
- f32/f64::mul_add contraction in hot scalar math (= C's -ffp-contract=on;
89 sites; wide SIMD ops untouched like C intrinsics). large_pyramid
now at parity with C (1387 vs 1373 ms serial)
- FloatW::get/set: direct lane load/store instead of vector-through-stack
round trip; layout asserted at compile time
- gather_bodies by reference (removes 20-register spill storm)
- per-worker capacity-preserving scratch for convex + mesh collide paths
(C-arena equivalent; mesh path allocated per triangle and serialized
the parallel collide pass on allocator locks)
- update_contact: borrow shapes instead of cloning (deep compound
geometry clones + cross-worker Arc traffic; junkyard w=8 -39%)
- scheduler semaphore: two-level atomic fast path (C uses
dispatch_semaphore_t; old Mutex+Condvar locked every enqueue)
- SyncSlice::get_ref/get_mut unchecked indexing under the existing
unsafe contract, debug_assert-guarded (-6% serial)
- README/PORTING: new numbers, FMA sync conventions, known remainders
179/185/179 tests green (default/double-precision/disable-simd), zero
warnings.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Full engine port in libs/box3d: math, geometry, GJK/TOI, hull builder,
dynamic tree, manifolds, constraint graph, solver (serial, scalar SIMD
path), all 8 joint types, sensors, mover, world API. 147 ported C unit
tests green in debug and release. See libs/box3d/README.md for the
upstream revision and sync notes, PORTING.md for conventions.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
