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perf(h264): hoist encoder SAD dispatch per block #529

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Merged
gunwooterry merged 3 commits into from
Nov 8, 2026
Merged

perf(h264): hoist encoder SAD dispatch per block #529

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fb595c9
perf(h264): hoist SAD dispatch out of score rows
gunwooterry Nov 8, 2026
fba8f67
perf(h264): inline the per-row SAD call
gunwooterry Nov 8, 2026
daa63d4
chore(h264): merge main into SAD dispatch
gunwooterry Nov 8, 2026
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126 changes: 122 additions & 4 deletions crates/coreav-h264-encoder/src/inter.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -149,12 +149,10 @@ fn score_rows(
motion_cost: u64,
cutoff: Option<u64>,
) -> Result<Option<u64>> {
let sad = crate::kernels::Sad::new(width)?;
let mut score = motion_cost;
for (original, predicted) in source.chunks(STRIDE).zip(predicted.chunks(stride)) {
score += crate::kernels::sad(
original.get(..width).ok_or(Error::Internal)?,
predicted.get(..width).ok_or(Error::Internal)?,
)?;
score += sad.row(original, predicted)?;
if cutoff.is_some_and(|limit| score > limit) {
return Ok(None);
}
Expand Down Expand Up @@ -1928,6 +1926,126 @@ mod tests {
assert!(motions.ranked.contains(&Some((16, 8, mv))));
}

fn per_row_scores(
source: &[u8],
predicted: &[u8],
stride: usize,
width: usize,
motion_cost: u64,
cutoff: Option<u64>,
) -> Result<Option<u64>> {
let mut score = motion_cost;
for (original, predicted) in source.chunks(STRIDE).zip(predicted.chunks(stride)) {
score += crate::kernels::sad(
original.get(..width).ok_or(Error::Internal)?,
predicted.get(..width).ok_or(Error::Internal)?,
)?;
if cutoff.is_some_and(|limit| score > limit) {
return Ok(None);
}
}
Ok(Some(score))
}

#[test]
fn block_sad_dispatch_matches_per_row_scores_cutoffs_and_failures() {
let mut seed = 0x5ad0_d15b_a7c4_e001u64;
let mut next = || {
seed ^= seed << 13;
seed ^= seed >> 7;
seed ^= seed << 17;
seed
};
let mut compared = 0;
for width in 0..=20 {
for height in 1..=16 {
for stride in [width.max(1), 16, 21, STRIDE, 64] {
let extremes = next() % 4 == 0;
let mut sample = || {
let value = next();
if extremes {
[0, 255][value as usize % 2]
} else {
value as u8
}
};
let source: Vec<u8> = (0..(height - 1) * STRIDE + width.max(1))
.map(|_| sample())
.collect();
let predicted: Vec<u8> = (0..(height - 1) * stride + width.max(1) + 3)
.map(|_| sample())
.collect();
let motion_cost = next() % 512;
let mut prefixes = vec![motion_cost];
if width <= 16 {
for (row, original) in source.chunks(STRIDE).enumerate() {
let start = row * stride;
let total = original
.iter()
.take(width)
.zip(&predicted[start..start + width])
.map(|(&a, &b)| u64::from(a.abs_diff(b)))
.sum::<u64>();
prefixes.push(prefixes.last().unwrap() + total);
}
assert_eq!(
score_rows(&source, &predicted, stride, width, motion_cost, None),
Ok(Some(*prefixes.last().unwrap()))
);
}
let mut cutoffs = vec![None, Some(0), Some(u64::MAX)];
for &prefix in &prefixes {
cutoffs.extend([prefix.checked_sub(1), Some(prefix), Some(prefix + 1)]);
}
let short = (height - 1) * stride + width.max(1) - 1;
for cutoff in cutoffs {
for (source, predicted) in [
(&source[..], &predicted[..]),
(&source[..source.len() - 1], &predicted[..]),
(&source[..], &predicted[..short]),
] {
assert_eq!(
score_rows(source, predicted, stride, width, motion_cost, cutoff),
per_row_scores(
source,
predicted,
stride,
width,
motion_cost,
cutoff
),
"width {width} height {height} stride {stride} cutoff {cutoff:?}"
);
compared += 1;
}
}
}
}
}
assert!(compared > 50_000);
}

#[test]
fn block_sad_keeps_row_cutoffs_equal_score_ties_and_admission() {
let source = [10u8; STRIDE * 3 + 16];
let mut predicted = [0u8; 16 * 4];
let rows = |predicted: &[u8], cutoff| score_rows(&source, predicted, 16, 16, 5, cutoff);
assert_eq!(rows(&predicted, None), Ok(Some(645)));
assert_eq!(rows(&predicted, Some(645)), Ok(Some(645)));
assert_eq!(rows(&predicted, Some(644)), Ok(None));
assert_eq!(rows(&predicted, Some(165)), Ok(None));
assert_eq!(rows(&predicted, Some(4)), Ok(None));
assert_eq!(rows(&predicted[..15], Some(0)), Err(Error::Internal));
predicted[16 * 3..].fill(10);
assert_eq!(rows(&predicted, Some(485)), Ok(Some(485)));
assert_eq!(rows(&predicted, Some(484)), Ok(None));
assert_eq!(
score_rows(&source, &predicted, 16, 17, 5, None),
Err(Error::Internal)
);
assert_eq!(score_rows(&[], &[], 16, 16, 7, Some(0)), Ok(Some(7)));
}

#[test]
fn cheap_finalists_keep_protected_seeds_and_deterministic_ties() {
let mut motions = Motions::new();
Expand Down
71 changes: 64 additions & 7 deletions crates/coreav-h264-encoder/src/kernels.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,19 +16,45 @@ pub(crate) fn pixels() -> Auto {
}

pub(crate) fn sad(a: &[u8], b: &[u8]) -> Result<u64> {
if a.len() != b.len() || a.len() > 16 {
if a.len() != b.len() {
return Err(Error::Internal);
}
Sad::new(a.len())?.row(a, b)
}

#[derive(Clone, Copy)]
pub(crate) struct Sad {
width: usize,
#[cfg(all(target_arch = "x86_64", not(feature = "scalar")))]
{
if let Some(simd) = arithmetic() {
simd: Option<crate::simd::Avx2>,
}

impl Sad {
#[inline]
pub(crate) fn new(width: usize) -> Result<Self> {
if width > 16 {
return Err(Error::Internal);
}
Ok(Self {
width,
#[cfg(all(target_arch = "x86_64", not(feature = "scalar")))]
simd: arithmetic(),
})
}

#[inline]
pub(crate) fn row(self, a: &[u8], b: &[u8]) -> Result<u64> {
let a = a.get(..self.width).ok_or(Error::Internal)?;
let b = b.get(..self.width).ok_or(Error::Internal)?;
#[cfg(all(target_arch = "x86_64", not(feature = "scalar")))]
if let Some(simd) = self.simd {
return Ok(simd.sad(a, b));
}
Ok(a.iter()
.zip(b)
.map(|(&a, &b)| u64::from(a.abs_diff(b)))
.sum())
}
Ok(a.iter()
.zip(b)
.map(|(&a, &b)| u64::from(a.abs_diff(b)))
.sum())
}

#[cfg(all(target_arch = "x86_64", not(feature = "scalar")))]
Expand Down Expand Up @@ -237,6 +263,37 @@ mod tests {
assert_eq!(sad(&[0; 16], &[0; 15]), Err(Error::Internal));
}

#[test]
fn block_sad_admits_width_once_and_reads_exactly_width_bytes_per_row() {
assert!(Sad::new(17).is_err());
let mut seed = 0x3c6e_f372_fe94_f82bu64;
for width in 0..=16 {
let block = Sad::new(width).unwrap();
for _ in 0..256 {
let mut a = [0; 24];
let mut b = [0; 24];
for v in a.iter_mut().chain(&mut b) {
seed ^= seed << 13;
seed ^= seed >> 7;
seed ^= seed << 17;
*v = seed as u8;
}
let want = a[..width]
.iter()
.zip(&b[..width])
.map(|(&a, &b)| u64::from(a.abs_diff(b)))
.sum();
assert_eq!(block.row(&a, &b), Ok(want));
assert_eq!(block.row(&a[..width], &b[..width]), Ok(want));
assert_eq!(sad(&a[..width], &b[..width]), Ok(want));
if width > 0 {
assert_eq!(block.row(&a[..width - 1], &b), Err(Error::Internal));
assert_eq!(block.row(&a, &b[..width - 1]), Err(Error::Internal));
}
}
}
}

#[test]
fn scalar_feature_overrides_pixel_dispatch() {
#[cfg(feature = "scalar")]
Expand Down
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