Small value neutronnova#124
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Add support for accumulating field × small_int products (i32, i64, i128) with delayed modular reduction using generic Barrett reduction: - SmallValueField<V> trait for small integer ↔ field conversion - WideMul trait for widening multiplication - BarrettReductionConstants with compile-time computed μ = ⌊2^512/p⌋ - SignedWideLimbs<N> accumulator for signed product sums - DelayedReduction<i32/i64/i128> implementations for all fields
This replaces expensive field multiplications with native integer
arithmetic during the first ℓ₀ rounds when polynomial values are
guaranteed small.
Key components:
Lagrange accumulator infrastructure (src/lagrange_accumulator/):
- LagrangeAccumulators: precomputed A_i(v, u) values for all rounds
- LagrangeIndex/LagrangePoint/LagrangeHatPoint: type-safe domain indices
- LagrangeBasisFactory: barycentric Lagrange basis with O(D) evaluation
- extend_to_lagrange_domain: batch extension from {0,1}^ℓ₀ to U_D^ℓ₀
- EqRoundFactor: tracks α = eq(τ_{<i}, r_{<i}) across rounds
- Csr: compressed sparse row storage (2 allocations vs N+1 for Vec<Vec>)
Performance optimizations:
- Thread-local SpartanThreadState eliminates per-iteration allocations
- Delayed modular reduction via SignedWideLimbs accumulators
- Skip binary betas (Az·Bz = Cz on {0,1}^n for satisfying witnesses)
- Batched eq-weighted binding in transition phase
API:
- SmallValue trait: WideMul + Copy + Zero + Add + Sub + Send + Sync
- SmallValueEngine<SV>: blanket impl consolidates field requirements
- prove_cubic_small_value<E, SV, const LB>: main entry point
The prove_cubic_small_value function produces identical proofs to the
standard prove_cubic_with_three_inputs, verified via equivalence tests.
Collaborator
|
@wu-s-john, thanks for the PR! Any idea if we can make thread-1 performance better than baseline? |
Splits the small-value accumulator prep/prove path out of neutronnova_zk
into a new small_neutronnova_zk module. Along with the move:
- Consolidates build_accumulators_neutronnova: the full-small (l0 == ell_b)
and partial-small (l0 < ell_b) variants now live in one function;
_partial is removed from the lagrange_accumulator surface.
- Factors the bit-reversed prefix gather + Lagrange-extend pattern into
bit_rev_prefix_table and gather_and_extend_prefix helpers in
lagrange_accumulator::extension, shared by the merged builder,
build_extended_prefix_mle_evals, and the test that compares them.
- Simplifies the small-value casting API: removes
vec_to_small_for_extension_with_context; the call sites in
build_small_abc wrap with .map_err to prepend "accumulator prep
{matrix} layer={idx}" to the context.
- Drops the unused SmallSparseMatrix path from r1cs::sparse.
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Run the small value NeutronNova code using
RUSTFLAGS="-C target-cpu=native" cargo bench --bench sha256_neutronnovaThis implementation of small value NeutronNova seems to be more performant than the current existing