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Add Main10 residuals to prediction one checked row at a time instead of one checked sample at a time, in the opt-in HEVC decoder's kernel crate.
8-bit and Main10 now share one row routine, with the depth's sample bound as a constant. Output, error kinds and error precedence are unchanged.
Background
The 8-bit path of add_residual already borrowed each row once and added it in a tight loop. The Main10 path read every prediction and residual sample through a bounds-checked accessor and wrote every output sample through another, twice per block. A throwaway count that removed bounds checks across the hottest single-thread paths (entropy engine, residual coding, coding-tree walker, inverse and intra kernels) put this Main10 path first, at about 4% of whole-process instructions on the two Main10 references. This change reaches that gain in safe Rust, so it needs no unsafe site. Refs #22.
What changes
Decoded output is unchanged. Main10 reconstruction does less work per residual block.
Covered: add_residual at both supported bit depths and all four transform sizes.
Not covered: the inverse transforms, intra prediction, inter combination, the walker's cell lookups, CABAC, default features and CLI behaviour.
After merging: None.
Decisions
Reuse the existing 8-bit row routine with a constant sample bound, rather than adding a Main10 copy or an unsafe unchecked accessor. Safe row borrowing removes the per-sample checks the count identified, and one routine keeps the two depths identical apart from the bound.
Keep the bound a const generic. A first version passed it at run time and made the 8-bit path about 0.3–0.5% slower in instructions. With the constant, the 8-bit instruction counts match main exactly.
Saturating i32 addition followed by a clamp to the depth's range equals the previous i64 sum and clip for every i32 residual and every valid prediction sample, because the clamp bounds lie inside i32.
Evidence
Verification run: cargo test -p coreav-kernels-hevc --features native-hevc passes (48 tests) on macOS arm64. Strict Clippy passes for coreav-kernels-hevc with native-hevc, with and without scalar, and for coreav-hevc with native-hevc. New tests check Main10 output against the literal sum-and-clip over the full residual domain, short last rows and untouched padding, and check that an invalid Main10 prediction sample at any position fails before any output write.
On GitHub Actions x86-64 (single CPU, one decoder thread, eight-picture prefixes of four existing lossy reference inputs), every arm matched the pinned FFmpeg 9 oracle picture by picture. Whole-process instructions against main at the final code: 8-bit inputs unchanged (0.00%, 0.00%); Main10 inputs 4.48% and 6.52% fewer. Paired median wall time on Main10 improved 2.2% and 2.7%, and 8-bit stayed within noise (-0.3%, -0.2%). These are reference figures on shared runners, not a timed claim.
Similarity at 2f88ac3d6a91976c7d4f0d40d5ffe99bde35eefc against the main allowlist passes: 112 spans of 50 or more tokens, 0 not allowlisted, 0 problems, 0 stale entries.
The HEVC add_residual path now uses a depth-specific maximum for prediction validation and output clamping. Main10 tests cover block sizes 4, 8, 16, and 32, including out-of-range samples and row padding.
Changes: HEVC residual addition
Layer / File(s)
Summary
Depth-specific dispatch and bounds crates/coreav-kernels-hevc/src/inverse.rs
add_residual uses add_rows for supported block sizes. It validates predictions and clamps output using the selected maximum.
No actionable issue is established for the depth-specific residual change. Normal validation, including the pending full conformance runs, can proceed before merge.
Architecture risk: Medium · up to 2f88a
The change affects 1 system.
Changed systems:crates
Architecture concerns
No architecture-level concerns identified.
Review details
Systems and components
observed — crates (service) was modified; 2 changed files map to changed impact.
Before / after behavior
observed — Modified behavior in crates/coreav-kernels-hevc/src/inverse.rs: add_residual now dispatches to add_rows for every supported block size. The former 8-bit-specific dispatch and separate higher-depth scalar implementation are removed; 8-bit uses a maximum of 255 and other depths use 1023.
observed — Modified behavior in crates/coreav-kernels-hevc/src/inverse.rs: Prediction validation now compares samples with the selected MAX rather than the fixed 8-bit limit of 255.
observed — Modified behavior in crates/coreav-kernels-hevc/src/inverse.rs: Output samples are clamped to 0 through MAX instead of 0 through 255, using the same depth-specific bound as validation.
observed — Modified behavior in crates/coreav-kernels-hevc/src/inverse/tests.rs: Adds a Main10 test that checks residual addition against a 0–1023 clamp for varied residuals and sampled predictions across four block sizes, using distinct prediction, residual, and output strides and checking output row padding.
Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
Check name
Status
Explanation
Title check
The title "perf(hevc): add Main10 residuals by rows" follows Conventional Commits and names the main change: Main10 residual addition in the HEVC kernel now runs one checked row at a time. The raw sum…
Description check
The description follows the repository template in structure and is substantively complete. It has a TL;DR with two bullets, a Background that explains the Main10 bounds-check cost and cites Refs #22,…
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
Full details: Title check
Explanation
The title "perf(hevc): add Main10 residuals by rows" follows Conventional Commits and names the main change: Main10 residual addition in the HEVC kernel now runs one checked row at a time. The raw summary and objectives confirm that add_residual now uses a generic row helper for both bit depths, with the Main10 path being the performance focus. The title is 40 characters, under the 50-character guideline, and is specific enough for a teammate scanning history.
Full details: Description check
Explanation
The description follows the repository template in structure and is substantively complete. It has a TL;DR with two bullets, a Background that explains the Main10 bounds-check cost and cites Refs #22, a What changes section with covered and not-covered scope and a post-merge note, a Decisions section with three bullets (reuse of the row routine, const generic bound, and the i32 saturation equivalence), and an Evidence section with test, Clippy, benchmark, and similarity results plus the DCO and copying checkboxes. Minor gaps: the template's Mermaid How it works section is absent, though the diff sits within one kernel layer and the template says to delete that section in that case. The 'Needs the maintainer' section is also omitted, which is correct because no item applies. The TL;DR does not fully follow the 50-character title rule for every part, but the title itself is 40 characters. The conformance runs are still in progress, which the description states.
Full details: Docstring Coverage
Explanation
Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 4 functions across 2 files.
Resolution
Write docstrings for the functions missing them to satisfy the coverage threshold.
Finishing Touches
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Reviewing files that changed from the base of the PR and between 3951933 and 2f88ac3.
Files selected for processing: 2
crates/coreav-kernels-hevc/src/inverse.rs
crates/coreav-kernels-hevc/src/inverse/tests.rs
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Reviewed head 2f88ac3d6a91976c7d4f0d40d5ffe99bde35eefc.
The accepted sample depths are exactly 8 and 10: BitDepth::new rejects 9, and SPS admission rejects unequal component depths. The dispatch therefore selects the correct 255/1023 limit for every currently admitted component.
For nonnegative valid predictions and every i32 residual, negative addition overflow is impossible; positive overflow already implies clipping to the upper sample bound. Saturating i32 addition followed by the clamp is consequently equivalent to the former i64 sum and clip. Size checks and the complete pre-write prediction validation remain intact, and checked block extents make the row arithmetic valid.
The 8-bit specialization retains the same validation and arithmetic. Residual addition has no separate SIMD dispatch, so both feature modes use this routine. I independently ran the kernel crate tests with native-hevc and native-hevc,scalar on macOS arm64: 48 passed in each mode. The added tests cover 10-bit clipping boundaries, signed residual extremes, independent strides, short final rows, padding and invalid samples at every position. I did not rerun instruction-count measurements.
Both full workflow_dispatch runs succeeded at this exact head: automatic and forced scalar. All four census shards and both vector jobs succeeded; the automatic run's Linux and macOS kernel-differential jobs also succeeded. The scalar run intentionally skips the separate differential job.
No outstanding Greptile findings are present; CodeRabbit is approved with no open review threads. The diff, commit messages and PR description contain no corpus names or CoreAV-versus-FFmpeg performance figures; the displayed performance deltas compare against main.
Non-blocking: docs/design/hevc-inverse-reconstruction.md still describes ten-bit reconstruction as unchanged and a future follow-up. Its scope description should eventually reflect this extension.
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TL;DR
Background
The 8-bit path of
add_residualalready borrowed each row once and added it in a tight loop. The Main10 path read every prediction and residual sample through a bounds-checked accessor and wrote every output sample through another, twice per block. A throwaway count that removed bounds checks across the hottest single-thread paths (entropy engine, residual coding, coding-tree walker, inverse and intra kernels) put this Main10 path first, at about 4% of whole-process instructions on the two Main10 references. This change reaches that gain in safe Rust, so it needs nounsafesite. Refs #22.What changes
Decoded output is unchanged. Main10 reconstruction does less work per residual block.
add_residualat both supported bit depths and all four transform sizes.After merging: None.
Decisions
unsafeunchecked accessor. Safe row borrowing removes the per-sample checks the count identified, and one routine keeps the two depths identical apart from the bound.i32addition followed by a clamp to the depth's range equals the previousi64sum and clip for everyi32residual and every valid prediction sample, because the clamp bounds lie insidei32.Evidence
Verification run:
cargo test -p coreav-kernels-hevc --features native-hevcpasses (48 tests) on macOS arm64. Strict Clippy passes forcoreav-kernels-hevcwithnative-hevc, with and withoutscalar, and forcoreav-hevcwithnative-hevc. New tests check Main10 output against the literal sum-and-clip over the full residual domain, short last rows and untouched padding, and check that an invalid Main10 prediction sample at any position fails before any output write.On GitHub Actions x86-64 (single CPU, one decoder thread, eight-picture prefixes of four existing lossy reference inputs), every arm matched the pinned FFmpeg 9 oracle picture by picture. Whole-process instructions against main at the final code: 8-bit inputs unchanged (0.00%, 0.00%); Main10 inputs 4.48% and 6.52% fewer. Paired median wall time on Main10 improved 2.2% and 2.7%, and 8-bit stayed within noise (-0.3%, -0.2%). These are reference figures on shared runners, not a timed claim.
Similarity at
2f88ac3d6a91976c7d4f0d40d5ffe99bde35eefcagainst the main allowlist passes: 112 spans of 50 or more tokens, 0 not allowlisted, 0 problems, 0 stale entries.Links: full conformance at this head passed, automatic (https://github.com/coreav-dev/coreav/actions/runs/42546351203) and forced scalar (https://github.com/coreav-dev/coreav/actions/runs/42546354225).
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