Re-derives the campaign's rtop8 breakthrough (fuse/rtop8-par @ b32439b,
commits 48b3a98 + b32439b) cleanly onto origin/dev @ 61004dc (post-#391
split), dropping the cb-chain commit (1130ac9) that branch was stacked
on. cb-chain touched only c/glm.c (now split into c/colibri.c); rtop8
touches only c/backend_metal.{h,mm} and c/tests/test_backend_metal.mm —
disjoint files, verified zero cb-chain remnants in this diff.
- r_top8_par: one SIMDGROUP per row (blocked lane ownership, taken
bitmask, shuffle-down argmax with ties->lower-index) replicating the
serial r_top8's first-max-wins ascending order exactly; topp/normk/
rscale tail verbatim on lane 0. Bench: serial 0.465 ms/layer (~55% of
the layer CB), parallel ~93x faster on the kernel, bit-exact.
- COLI_RTOP8 gate, default ON (renamed and inverted from the campaign's
COLI_RTOP8_PAR=0-default gate; COLI_RTOP8=0 is the opt-out escape).
- Expert-count generality (new hard requirement, REAP E=168 packages):
the parallel kernel's E<=256 contract is now enforced at EVERY call
site in host code (g_rtop8_width_ok / E<=256 checked before selecting
the pipeline), not just as an in-kernel defensive no-op -- closes a
latent gap where the campaign's SIMD-width guard only protected the
engine's automatic dispatch, not the standalone coli_metal_rtop8(par=1,
...) probe function metal-test itself uses. Out-of-contract requests
(E>256, or non-32-wide SIMD) now transparently run the serial kernel
instead of silently no-op'ing.
- metal-test: 16 new cases -- the campaign's 10-case exact-match fuzz
(now E-parametric) plus 6 new E-generality cases: E=168 (REAP) generic
+ massed-dup-ties, E=24 (<32 lane width) generic + ALL-EQUAL ties,
E=200 (a lane straddles the E boundary -- per=ceil(200/32)=7 doesn't
divide 200, so lane 28's ch[] block mixes 4 real indices with 3
sentinel ones; input is constructed to force those 4 into the top-8
deterministically, and the test asserts they were actually selected,
not just that serial==parallel), and E=257 (out-of-contract, proves
the auto-serial-fallback engages: this case is confirmed load-bearing
-- it fails without the new host-side guard). 15 stock + 10 ported +
6 new = 31 total metal-test cases.
Builds (METAL=0/1) and full C/python suites verified unchanged vs stock
61004dc (0 new warnings, identical pass counts). On-box A/B on this
branch is pending (see PR_BODY.md) -- no model runs performed here.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
monotophic
9f30916003