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fix(math): remove unnecessary scratchpad clone in BatchInversion #1370

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Merged
jimpo merged 1 commit into from
Jan 5, 2026
Merged

fix(math): remove unnecessary scratchpad clone in BatchInversion #1370

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65 changes: 36 additions & 29 deletions crates/math/src/batch_invert.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -142,39 +142,46 @@ fn min_scratchpad_size(mut n: usize) -> usize {

impl<P: PackedField> BatchInversion<P> {
fn batch_invert_nonzero(&mut self, elements: &mut [P]) {
self.batch_invert_nonzero_with_scratchpad(elements, &mut self.scratchpad.clone());
batch_invert_nonzero_with_scratchpad(
elements,
&mut self.scratchpad,
self.scalar_inverter.as_deref_mut(),
);
}
}

fn batch_invert_nonzero_with_scratchpad(&mut self, elements: &mut [P], scratchpad: &mut [P]) {
debug_assert!(!elements.is_empty());

if elements.len() == 1 {
let packed = &mut elements[0];
if P::WIDTH == 1 {
// Direct scalar inversion
let scalar = packed.get(0);
let inv = scalar
.invert()
.expect("precondition: elements contains no zeros");
packed.set(0, inv);
} else {
// Unpack, batch invert scalars, repack
let mut scalars = packed.into_iter().collect::<Vec<_>>();
self.scalar_inverter
.as_mut()
.expect("scalar_inverter must be Some when WIDTH > 1")
.invert_nonzero(&mut scalars);
*packed = P::from_scalars(scalars);
}
return;
fn batch_invert_nonzero_with_scratchpad<P: PackedField>(
elements: &mut [P],
scratchpad: &mut [P],
scalar_inverter: Option<&mut BatchInversion<P::Scalar>>,
) {
debug_assert!(!elements.is_empty());

if elements.len() == 1 {
let packed = &mut elements[0];
if P::WIDTH == 1 {
// Direct scalar inversion
let scalar = packed.get(0);
let inv = scalar
.invert()
.expect("precondition: elements contains no zeros");
packed.set(0, inv);
} else {
// Unpack, batch invert scalars, repack
let mut scalars = packed.into_iter().collect::<Vec<_>>();
scalar_inverter
.expect("scalar_inverter must be Some when WIDTH > 1")
.invert_nonzero(&mut scalars);
*packed = P::from_scalars(scalars);
}

let next_layer_len = elements.len().div_ceil(2);
let (next_layer, remaining) = scratchpad.split_at_mut(next_layer_len);
product_layer(elements, next_layer);
self.batch_invert_nonzero_with_scratchpad(next_layer, remaining);
unproduct_layer(next_layer, elements);
return;
}

let next_layer_len = elements.len().div_ceil(2);
let (next_layer, remaining) = scratchpad.split_at_mut(next_layer_len);
product_layer(elements, next_layer);
batch_invert_nonzero_with_scratchpad(next_layer, remaining, scalar_inverter);
unproduct_layer(next_layer, elements);
}

/// Computes element-wise products of top and bottom halves.
Expand Down