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Simplify compress_elements #2155

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Simplify compress_elements #2155

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093c612
perf: simplify PoseidonSponge::compress_elements
ljedrz Nov 3, 2023
4e5e43b
Merge branch 'testnet3' into perf/simplify_compress_elements
howardwu Nov 24, 2023
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22 changes: 8 additions & 14 deletions algorithms/src/crypto_hash/poseidon.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -333,7 +333,7 @@ impl<F: PrimeField, const RATE: usize> PoseidonSponge<F, RATE, 1> {

/// Compress every two elements if possible.
/// Provides a vector of (limb, num_of_additions), both of which are F.
pub fn compress_elements<TargetField: PrimeField, I: Iterator<Item = (F, F)>>(
fn compress_elements<TargetField: PrimeField, I: Iterator<Item = F>>(
&self,
mut src_limbs: Peekable<I>,
ty: OptimizationType,
Expand All @@ -343,30 +343,25 @@ impl<F: PrimeField, const RATE: usize> PoseidonSponge<F, RATE, 1> {

let params = get_params(TargetField::size_in_bits(), F::size_in_bits(), ty);

// Prepare a reusable vector to be used in overhead calculation.
let mut num_bits = Vec::new();
let overhead = crate::overhead!(F::one() + F::one(), &mut Vec::new());

while let Some(first) = src_limbs.next() {
let second = src_limbs.peek();

let first_max_bits_per_limb = params.bits_per_limb + crate::overhead!(first.1 + F::one(), &mut num_bits);
let second_max_bits_per_limb = if let Some(second) = second {
params.bits_per_limb + crate::overhead!(second.1 + F::one(), &mut num_bits)
} else {
0
};
let first_max_bits_per_limb = params.bits_per_limb + overhead;
let second_max_bits_per_limb = if second.is_some() { first_max_bits_per_limb } else { 0 };

if let Some(second) = second {
if first_max_bits_per_limb + second_max_bits_per_limb <= capacity {
let adjustment_factor = &self.adjustment_factor_lookup_table[second_max_bits_per_limb];

dest_limbs.push(first.0 * adjustment_factor + second.0);
dest_limbs.push(first * adjustment_factor + second);
src_limbs.next();
} else {
dest_limbs.push(first.0);
dest_limbs.push(first);
}
} else {
dest_limbs.push(first.0);
dest_limbs.push(first);
}
}

Expand Down Expand Up @@ -421,8 +416,7 @@ impl<F: PrimeField, const RATE: usize> PoseidonSponge<F, RATE, 1> {
.into_iter()
.flat_map(|elem| {
let limbs = Self::get_limbs_representations(&elem, ty);
limbs.into_iter().map(|limb| (limb, F::one()))
// specifically set to one, since most gadgets in the constraint world would not have zero noise (due to the relatively weak normal form testing in `alloc`)
limbs.into_iter()
})
.peekable();

Expand Down