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perf(stark): skip fixed 0/1 muls in LogUp fingerprint accumulation #696

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perf(stark): skip fixed 0/1 muls in LogUp fingerprint accumulation #696

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29 changes: 18 additions & 11 deletions crypto/stark/src/lookup.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -668,7 +668,11 @@ impl BusValue {
}
}
}
*acc += &result * &alpha_powers[alpha_offset];
// Fixed-zero bus elements (bus-width padding) contribute nothing —
// skip the F×E multiply. (α⁰ = 1 covers the bus-id term separately.)
if result != FieldElement::<F>::zero() {
*acc += &result * &alpha_powers[alpha_offset];
}
1
}
}
Expand Down Expand Up @@ -778,7 +782,11 @@ impl BusValue {
}
}
}
*acc += result * &alpha_powers[alpha_offset];
// Fixed-zero bus elements (bus-width padding) contribute nothing —
// skip the F×E multiply.
if result != FieldElement::<A>::zero() {
*acc += result * &alpha_powers[alpha_offset];
}
1
}
}
Expand Down Expand Up @@ -1465,10 +1473,6 @@ where
.max()
.unwrap_or(0);
let alpha_powers = compute_alpha_powers(alpha, max_bus_elements);
let bus_ids: Vec<FieldElement<F>> = interactions
.iter()
.map(|i| FieldElement::<F>::from(i.bus_id))
.collect();
let shifts = PackingShifts::<F>::new();
let n = interactions.len();

Expand All @@ -1480,9 +1484,11 @@ where
// Phase 1 — fingerprints, laid out as [int_0 rows…, int_1 rows…].
// fp[k*chunk_len + i] = interaction k at row chunk_start+i.
let mut fingerprints: Vec<FieldElement<E>> = Vec::with_capacity(n * chunk_len);
for (k, interaction) in interactions.iter().enumerate() {
for interaction in interactions.iter() {
// α⁰ = 1: the bus-id term needs no multiply — embed it into E once.
let bus_id_e = FieldElement::<E>::from(interaction.bus_id);
for row in chunk_start..chunk_start + chunk_len {
let mut lc = &bus_ids[k] * &alpha_powers[0];
let mut lc = bus_id_e.clone();
let mut alpha_offset = 1;
for bv in &interaction.values {
alpha_offset += bv.accumulate_fingerprint(
Expand All @@ -1502,7 +1508,8 @@ where
if n == 1 {
let interaction = interactions[0];
for (i, row) in (chunk_start..chunk_start + chunk_len).enumerate() {
let mut base_elements: Vec<FieldElement<F>> = vec![bus_ids[0].clone()];
let mut base_elements: Vec<FieldElement<F>> =
vec![FieldElement::<F>::from(interaction.bus_id)];
base_elements.extend(
interaction
.values
Expand Down Expand Up @@ -1677,8 +1684,8 @@ fn compute_fingerprint_from_step<A: IsSubFieldOf<B>, B: IsField>(
alpha_powers: &[FieldElement<B>],
shifts: &PackingShifts<A>,
) -> FieldElement<B> {
let bus_id_f: FieldElement<A> = FieldElement::from(interaction.bus_id);
let mut linear_combination = bus_id_f * &alpha_powers[0];
// α⁰ = 1: the bus-id term needs no multiply — embed it into B directly.
let mut linear_combination = FieldElement::<B>::from(interaction.bus_id);
let mut alpha_idx = 1;
for bv in &interaction.values {
alpha_idx += bv.accumulate_fingerprint_from_step(
Expand Down
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