# dav1d source snapshot

Verbatim subset of dav1d source pinned for use as reference
implementations of AV1 CDEF (cycle 5 of `daedalus-fourier`) and
potentially future AV1 kernels. dav1d is the canonical AV1 decoder
library (BSD-2-Clause, maintained by VideoLAN).

See `../../docs/k5_cdef_phase1_2.md` for the cycle 5 scope and
rationale.

## Upstream pin

- **Repository**: https://github.com/videolan/dav1d (canonical mirror
  of https://code.videolan.org/videolan/dav1d)
- **Tag**: `1.4.3` (last stable release in the 1.4.x line as of
  2026-05-18; pinned for reproducibility)
- **Snapshot fetched**: 2026-05-18 (UTC), via
  `https://raw.githubusercontent.com/videolan/dav1d/1.4.3/<path>`

## Files in this snapshot

All files are byte-for-byte copies of the upstream source at the
tagged commit, except `tables_cdef_subset.c` which is a hand-extracted
single-table copy from `src/tables.c` (see §"Why each file" below).

| Path | Lines | SHA-256 |
|---|---|---|
| `src/arm/64/cdef.S` | 520 | `88d048cbed93f168...` (TODO full hash) |
| `src/arm/64/util.S` | 278 | `582acd8e2b74a1e8...` |
| `src/arm/asm.S` | 335 | `6a22def2799876c4...` |
| `src/cdef_tmpl.c` | 331 | `26a7a5f9fda65c58...` |
| `include/common/intops.h` | 84 | `c1e7d52b421d6417...` |
| `src/tables_cdef_subset.c` | hand-extracted | — |

Full SHA-256s (regenerated by `phase 3` setup):

```sh
( cd external/dav1d-snapshot && sha256sum \
    src/arm/64/cdef.S src/arm/64/util.S src/arm/asm.S \
    src/cdef_tmpl.c include/common/intops.h )
```

## License

BSD-2-Clause. Copyright (c) 2018 VideoLAN and dav1d authors; (c) 2019
Martin Storsjö (NEON aarch64). Original copyright headers preserved
in each vendored file.

Notably cleaner license than the FFmpeg LGPL-2.1+ snapshot — dav1d's
BSD allows distribution of binaries without LGPL's "share linking
ability" requirements. For daedalus-fourier benches that link only
this snapshot, the binary inherits BSD-2-Clause. Benches that
combine both snapshots (none currently) inherit LGPL-2.1+ via
FFmpeg's stronger terms.

## Why each file

- **`src/arm/64/cdef.S`** — the NEON aarch64 implementation. Provides
  `dav1d_cdef_filter8_pri_sec_8bpc_neon` and pri-only / sec-only
  variants. The Phase 3 NEON baseline (M3₅) measures this symbol.

- **`src/arm/64/util.S`** — helper macros (`load_px_8`,
  `handle_pixel_8`, etc.) referenced by cdef.S.

- **`src/arm/asm.S`** — top-level GAS preamble (function/endfunc,
  movrel, register macros). dav1d's own version is similar to FFmpeg's
  but with different defines (PRIVATE_PREFIX dav1d_ etc.); Phase 6
  setup will identify the config.h shim needed for standalone
  assembly.

- **`src/cdef_tmpl.c`** — the C reference (templated; the
  `cdef_filter_block_c` core function is in here, expanded to
  `cdef_filter_block_8x8_c` via `cdef_fn(8, 8)`).

- **`include/common/intops.h`** — utility helpers (apply_sign,
  imin, imax, iclip, umin) used by cdef_tmpl.c.

- **`src/tables_cdef_subset.c`** — hand-extracted `dav1d_cdef_directions`
  table from `src/tables.c` (lines 400-414). Provides the only
  table symbol both `cdef.S` and `cdef_tmpl.c` reference externally.
  Pulling in the full `src/tables.c` (1013 lines) would chain-include
  the entire dav1d decoder, which is overkill for our purposes.
  See `tables_cdef_subset.c` header comment for line-range
  reference back to upstream.

## Re-vendoring procedure

Same as FFmpeg snapshot — see `../ffmpeg-snapshot/PROVENANCE.md`.

```sh
TAG=1.x.y
BASE=https://raw.githubusercontent.com/videolan/dav1d/$TAG
cd external/dav1d-snapshot
for f in src/arm/64/cdef.S src/arm/64/util.S src/arm/asm.S \
         src/cdef_tmpl.c include/common/intops.h; do
  curl -sSf -o "$f" "$BASE/$f"
done
# tables_cdef_subset.c needs manual re-extraction from
# upstream src/tables.c — search for "dav1d_cdef_directions ="
```

## Pending work (Phase 3+, next session)

- config.h shim for assembling cdef.S standalone (dav1d's defines
  differ from FFmpeg's; will identify exact list on first build)
- Standalone C reference for `cdef_filter_block_8x8_c` (this snapshot's
  `cdef_tmpl.c` references several private headers — easier to
  transcribe to a self-contained `tests/cdef_ref.c`)
- `tests/bench_neon_cdef.c` to capture M3₅ baseline