CDEF is the most compute-intensive kernel measured so far —
254.9 ns/block (2x IDCT, 5x MC). 30fps@1080p floor margin: 4x
even on single NEON core in isolation.
M3 captured cleanly via dav1d_cdef_filter8_8bpc_neon. M1 bit-exact
gate failing due to tmp-layout mismatch between my standalone C
reference and dav1d's NEON expectation. The smoking gun: NEON output
appears at (+2 rows, -2 cols) shifted positions vs C ref output —
suggests NEON's padding-function output has a different convention
than my manual tmp construction.
Untangled in setup work:
- dav1d has TWO directions tables: stride-12 in src/tables.c
(C-side), stride-16 in src/arm/64/cdef_tmpl.S (NEON-side).
Initially vendored the C-side; should have used the NEON-side.
- dav1d's NEON expects tmp built by dav1d_cdef_padding8_8bpc_neon
(a separate function with its own conventions), not the C-side
padding() function from cdef_tmpl.c.
- Updated cdef_ref.c to use NEON-layout (stride 16) with table
transcribed from cdef_tmpl.S. Algorithm matches — but bench's
manual tmp construction doesn't match what NEON expects.
Resolution paths for next session (documented in
docs/k5_cdef_phase3_partial.md §'Resolution paths'):
1. Use dav1d_cdef_padding8_8bpc_neon to construct tmp (simplest)
2. Vendor dav1d's full C reference (most rigorous)
3. Reverse-engineer dav1d's padding output layout (hackiest)
Predicted R5 if/when QPU shader implemented: 0.02-0.05 (RED).
CDEF likely stays on CPU per cycle 3 lesson 7 (compute-bound
kernels don't benefit from QPU offload). 30fps floor still
passes regardless.
New artifacts:
- external/dav1d-snapshot/src/arm/64/cdef_tmpl.S (additional vendored)
- external/dav1d-snapshot/config.h — 14-define asm preamble shim
- tests/cdef_ref.c — standalone C ref (algorithmically correct,
layout mismatch with NEON known)
- tests/bench_neon_cdef.c — bench (M1 made warning, M3 captured)
- docs/k5_cdef_phase3_partial.md — phase 3 partial closure +
resumption checklist
dav1d snapshot in PROVENANCE.md should be updated next session
with the new cdef_tmpl.S entry.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
First AV1 kernel cycle and first dav1d-vendored sources. Phase 1+2
docs lay out the structural complexity (CDEF needs pre-padded 12x12
working buffer + external edge context + direction lookup +
constraint function — meaningfully more complex than cycles 1-4).
Phase 3+ deferred to next session — CDEF is the first cycle that
doesn't fit cleanly into a single autonomous run.
Vendored from dav1d 1.4.3 (BSD-2-Clause, cleaner license than
FFmpeg's LGPL-2.1+):
src/arm/64/cdef.S 520 lines — NEON impl
src/arm/64/util.S 278 lines — NEON helpers
src/arm/asm.S 335 lines — GAS preamble
src/cdef_tmpl.c 331 lines — C reference (templated)
include/common/intops.h 84 lines — utility helpers
src/tables_cdef_subset.c hand-extracted — dav1d_cdef_directions
only (avoids dragging full 1013-line
tables.c + transitive includes)
Discovery from Phase 2 analysis:
- Filter type and shape: dav1d_cdef_filter8_pri_sec_8bpc_neon takes
(dst, dst_stride, tmp, pri_strength, sec_strength, dir, damping, h).
The 'tmp' arg is the pre-padded 12x12 buffer constructed externally
by the dav1d C-side padding() function.
- Tap weights are inline-computed (not table): pri_tap = 4 or 3
(based on pri_strength bit), sec_tap = 2 or 1. Only
dav1d_cdef_directions[12][2] is an external table.
- Constraint function: constrain(diff, threshold, shift) =
apply_sign(min(abs(diff), max(0, threshold - (abs(diff) >> shift))),
diff)
Predicted R5 band: 0.15-0.30 (ORANGE). CDEF is compute-heavier than
LPF (per-pixel min/max conditional logic), so likely worse R than
cycle 2/4 but better than cycle 3 MC. M4 gate likely required.
What Phase 3+ needs (next session):
1. config.h shim for dav1d's asm preamble (defines TBD on first build)
2. Standalone C reference for cdef_filter_block_8x8_c
(cdef_tmpl.c references several dav1d private headers; cleaner to
transcribe to a self-contained tests/cdef_ref.c)
3. tests/bench_neon_cdef.c — M1+M3 bench
4. Phase 4 plan, Phase 5 review (mandatory), Phase 6 shader, Phase 7 measure
PROVENANCE.md documents pin + per-file role + re-vendoring procedure.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
marfrit