perf(prover): run the first sumcheck round in the base field#471
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shreyas-londhe merged 5 commits intoJul 13, 2026
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Two #[ignore] probes for manual profiling: a size sweep (BF vs EF vs bn254, 2^14..2^20) and a 2^20 goldilocks-BF flamegraph + stage breakdown. Timing excludes scheme construction and harness clones (prove_setup builds inputs outside the timer; time_prove_core measures only commit + prove_noir), and the flame layer installs after fixture generation, so the numbers reflect the true prove core. Profiling-only deps (inferno, tracing-flame).
cargo fmt rewrapping of comments trimmed in earlier commits; no code change.
Round 1 of the Spartan sumcheck can consume base-field a, b, c directly (one mixed mul per point against the ext eq) instead of lifting them first; the fold at the first challenge does the lift. These helpers provide that round evaluation and fold, with parity against the existing fused ext path pinned by tests.
The witness bounds a, b, c were lifted to the extension before the sumcheck, paying ext arithmetic on base data for every round. The first round (half the sumcheck work) now consumes them directly — base products with one mixed mul per point against the ext eq — and the fold at the first challenge does the lift. Transcript values are unchanged (subfield arithmetic, same elements), so the verifier and proof format are untouched; bn254 rides the same path via Identity. ~5% prove @2^20 goldilocks-BF, no bn254 regression.
- prover: precompute 1/2 once and pass it into combined_round_message instead of recomputing a field inverse every round (transcript-identical) - deps: move inferno/tracing-flame to root [workspace.dependencies] - fixtures: relocate the single-commit timed prove into harness.rs and point the flamegraph probe at target/profile/
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CSP benchmarks
Prover time, peak RSS, peak heap, and verifier time are arithmetic means across the iterations. Peak heap comes from the largest Each metric cell shows the current value followed by the percentage delta against the latest successful Results
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zkfriendly
approved these changes
Jul 13, 2026
| alpha.push(alpha_0); | ||
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| // Fold at the first challenge, lifting the mles into the extension. | ||
| let folded_a = mixed_fold(embedding, &a, alpha_0); |
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mixed_fold breaks the prior fused fold/reduce path, adding four allocations and another scan. This is not a no-op for BN254 Identity. We can address this later since the focus is Goldilocks
shreyas-londhe
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Summary
Runs the first Spartan sumcheck round over the base field. After the witness became base-committed (#470), the opening round still lifted the
a, b, cmles into the extension before folding. This computes round 0's cubic evaluations directly on the base-field mles (one mixed base×ext multiply per point against the extensioneq), then lifts into the extension only at the round-0 challenge. It also extracts the per-round message construction into a sharedcombined_round_messagehelper and adds the base-field sumcheck primitives it needs. A pair of#[ignore]d profiling probes are included so the win is reproducible in-tree.Stacks on #470 (base-field witness commitment). Independent of the CI guard (#469).
Why
On the Goldilocks base-field path the witness mles are 64-bit
Field64, but the sumcheckeqand challenges live in the degree-3 extensionField64_3. Liftinga, b, cto the extension before the first fold pays extension-width multiplies for data that is still base-valued. Doing round 0 in the base field removes one round's worth of extension multiplies — ~5% prove-time at 2^20 on the goldilocks base-field path. bn254 rides the identity embedding, so its path is a no-op (base == ext) and its proofs are unchanged.What changed
provekit-common—common/src/utils/sumcheck.rsgainsmixed_sumcheck_map_reduceandmixed_fold: reduce/fold the leading variable of base-field mles against an extension-fieldeq/challenge. Because the base→ext embeddingmapis a ring homomorphism, fold-then-lift is bit-identical to the old lift-then-fold — pinned bytest_mixed_map_reduce_matches_liftedandtest_explicit_mixed_fold_matches_fused_fold.provekit-prover—prover/src/whir_r1cs.rs: round 0 is hoisted out of the sumcheck loop and computed on the base-field mles (the loop now runs1..m_0); the per-round coefficient combination (hhat + rho·g_poly, saved-value equality) is extracted verbatim intocombined_round_messageand shared by round 0 and the loop.provekit-backend-bn254—mavros_prove.rspasses the embedding (&Identity::new()) and the base-field mles into the prover; identity embedding ⇒ no-op, transcript unchanged.#[ignore]d) —tooling/provekit-fixtures/tests/profile.rs: a size sweep (BF vs EF vs bn254, 2^14..2^20) and a 2^20 goldilocks-BF flamegraph + stage breakdown. Timing excludes scheme construction and harness clones. Dev-depsinferno/tracing-flameare scoped toprovekit-fixturesonly.Transcript / soundness
The prover round messages, challenge draw order, and the separate ext blinding commitment are unchanged from #470 — the verifier is untouched and replays the identical Fiat-Shamir transcript. Round 0's base-field evaluations equal the old extension-lifted ones because
mapis a ring homomorphism (map(a·b − c) = map(a)·map(b) − map(c),map(0) = 0for zero-padding). Both bn254 and goldilocks fixtures still prove→verify.Out of scope (tracked separately)
Same as #470: this does not touch the Go
recursive-verifier/or theprovekit-gnarkbridge. The reported ~5% is from the local flamegraph probe, not a CI-enforced benchmark.Verification
cargo fmt --all --check,cargo clippy --all-targets --all-features,cargo build --all-targets --all-features— all green, no new warnings.cargo build --locked -p provekit-fixtures— mergedCargo.lockself-consistent with the newinferno/tracing-flamepins.provekit-common87 (incl. the base/ext parity tests),provekit-r1cs-compiler41.#[ignore]d.Commits
5 commits: profiling probes (ignored) · doc-comment rewrap · base-field sumcheck round helpers (
common) · first sumcheck round in the base field (prover+ bn254 call-site) · review follow-ups (hoist1/2inverse out of the per-round loop, move the profiling dev-deps to[workspace.dependencies], dedup the single-commit timed prove into the fixtures harness).