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Performance Optimization: dot_product_scalar iterator handling #363

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Performance Optimization: dot_product_scalar iterator handling #363

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a671bbc
bfv: optimize dot_product_scalar by avoiding redundant iterator clones
google-labs-jules[bot] Feb 1, 2026
d198414
bfv: optimize dot_product_scalar by zipping and collecting pairs
google-labs-jules[bot] Feb 1, 2026
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23 changes: 11 additions & 12 deletions crates/fhe/src/bfv/ops/dot_product.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -58,25 +58,24 @@ where
I: Iterator<Item = &'a Ciphertext> + Clone,
J: Iterator<Item = &'a Plaintext> + Clone,
{
let count = min(ct.clone().count(), pt.clone().count());
if count == 0 {
// Collect the zipped iterators to avoid multiple traversals and to stop at the
// length of the shorter iterator, preventing O(N) memory usage if one iterator is huge.
let pairs: Vec<(&Ciphertext, &Plaintext)> = izip!(ct, pt).collect();

if pairs.is_empty() {
return Err(Error::DefaultError(
"At least one iterator is empty".to_string(),
));
}
let ct_first = ct.clone().next().unwrap();
let count = pairs.len();
let ct_first = pairs[0].0;
let ctx = ct_first[0].ctx();

if izip!(ct.clone(), pt.clone()).any(|(cti, pti)| {
if pairs.iter().any(|(cti, pti)| {
cti.par != ct_first.par || pti.par != ct_first.par || cti.len() != ct_first.len()
}) {
return Err(Error::DefaultError("Mismatched parameters".to_string()));
}
if ct.clone().any(|cti| cti.len() != ct_first.len()) {
return Err(Error::DefaultError(
"Mismatched number of parts in the ciphertexts".to_string(),
));
}

let max_acc = ctx
.moduli()
Expand All @@ -91,8 +90,8 @@ where
let c = (0..ct_first.len())
.map(|i| {
poly_dot_product(
ct.clone().map(|cti| unsafe { cti.get_unchecked(i) }),
pt.clone().map(|pti| &pti.poly_ntt),
pairs.iter().map(|(cti, _)| unsafe { cti.get_unchecked(i) }),
pairs.iter().map(|(_, pti)| &pti.poly_ntt),
)
.map_err(Error::MathError)
})
Expand All @@ -106,7 +105,7 @@ where
})
} else {
let mut acc = Array::zeros((ct_first.len(), ctx.moduli().len(), ct_first.par.degree()));
for (ciphertext, plaintext) in izip!(ct, pt) {
for (ciphertext, plaintext) in pairs {
let pt_coefficients = plaintext.poly_ntt.coefficients();
for (mut acci, ci) in izip!(acc.outer_iter_mut(), ciphertext.iter()) {
let ci_coefficients = ci.coefficients();
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