From 50f24d1fc10c27c4b573397955b0f480e683171f Mon Sep 17 00:00:00 2001
From: Jan Ferdinand Sauer <ferdinand@neptune.cash>
Date: Tue, 1 Oct 2024 13:57:50 +0200
Subject: [PATCH] refactor: Use barycentric evaluation of dependency

---
 Cargo.toml                            |  2 +-
 triton-vm/benches/barycentric_eval.rs |  5 +--
 triton-vm/src/fri.rs                  | 49 +++++----------------------
 3 files changed, 12 insertions(+), 44 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 6ef0b1e8..19a045f6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -84,7 +84,7 @@ strum = { version = "0.26", features = ["derive"] }
 syn = "2.0"
 test-strategy = "0.4.0"
 thiserror = "1.0"
-twenty-first = "0.42.0-alpha.9"
+twenty-first = "0.42.0-alpha.10"
 unicode-width = "0.1"
 divan = "0.1.14"
 
diff --git a/triton-vm/benches/barycentric_eval.rs b/triton-vm/benches/barycentric_eval.rs
index 4e116b12..81c663a7 100644
--- a/triton-vm/benches/barycentric_eval.rs
+++ b/triton-vm/benches/barycentric_eval.rs
@@ -6,7 +6,8 @@ use itertools::Itertools;
 use rand::prelude::StdRng;
 use rand::Rng;
 use rand_core::SeedableRng;
-use triton_vm::fri::barycentric_evaluate;
+use twenty_first::math::polynomial::barycentric_evaluate;
+use twenty_first::prelude::XFieldElement;
 
 criterion_main!(benches);
 criterion_group!(
@@ -25,7 +26,7 @@ fn barycentric_eval<const LOG2_N: usize>(c: &mut Criterion) {
     c.bench_function(&format!("barycentric_evaluation_(1<<{LOG2_N})"), |b| {
         b.iter_batched(
             || ((0..1 << LOG2_N).map(|_| rng.gen()).collect_vec(), rng.gen()),
-            |(codeword, indeterminate)| barycentric_evaluate(&codeword, indeterminate),
+            |(cw, ind): (Vec<XFieldElement>, XFieldElement)| barycentric_evaluate(&cw, ind),
             BatchSize::SmallInput,
         )
     });
diff --git a/triton-vm/src/fri.rs b/triton-vm/src/fri.rs
index 2cdb9ce2..3f92a295 100644
--- a/triton-vm/src/fri.rs
+++ b/triton-vm/src/fri.rs
@@ -473,6 +473,9 @@ impl<'stream> FriVerifier<'stream> {
     fn assert_last_round_codeword_corresponds_to_low_degree_polynomial(
         &mut self,
     ) -> VerifierResult<()> {
+        // todo: remove once deprecated local function `barycentric_evaluate` is removed
+        use twenty_first::math::polynomial::barycentric_evaluate;
+
         if self.last_round_polynomial.degree() > self.last_round_max_degree.try_into().unwrap() {
             return Err(FriValidationError::LastRoundPolynomialHasTooHighDegree);
         }
@@ -626,33 +629,15 @@ fn codeword_as_digests(codeword: &[XFieldElement]) -> Vec<Digest> {
 /// Panics if the codeword is some length that is not a power of 2 or greater than (1 << 32).
 ///
 /// [Credit]: https://github.com/0xPolygonMiden/miden-vm/issues/568
+#[deprecated(
+    since = "0.42.2",
+    note = "use `twenty_first::math::polynomial::barycentric_evaluate` instead"
+)]
 pub fn barycentric_evaluate<FF: FiniteField + Mul<XFieldElement, Output = XFieldElement>>(
     codeword: &[FF],
     indeterminate: XFieldElement,
 ) -> XFieldElement {
-    let root_order = codeword.len().try_into().unwrap();
-    let generator = BFieldElement::primitive_root_of_unity(root_order).unwrap();
-    let domain_iter = (0..root_order)
-        .scan(bfe!(1), |acc, _| {
-            let to_yield = Some(*acc);
-            *acc *= generator;
-            to_yield
-        })
-        .collect_vec();
-
-    let domain_shift = domain_iter.iter().map(|&d| indeterminate - d).collect();
-    let domain_shift_inverses = XFieldElement::batch_inversion(domain_shift);
-    let domain_over_domain_shift = domain_iter
-        .into_iter()
-        .zip(domain_shift_inverses)
-        .map(|(d, inv)| d * inv);
-    let numerator = domain_over_domain_shift
-        .clone()
-        .zip(codeword)
-        .map(|(dsi, &abscis)| abscis * dsi)
-        .sum::<XFieldElement>();
-    let denominator = domain_over_domain_shift.sum::<XFieldElement>();
-    numerator / denominator
+    twenty_first::math::polynomial::barycentric_evaluate(codeword, indeterminate)
 }
 
 pub(crate) fn batch_barycentric_preprocess(
@@ -704,7 +689,6 @@ mod tests {
     use assert2::assert;
     use assert2::let_assert;
     use itertools::Itertools;
-    use proptest::collection::vec;
     use proptest::prelude::*;
     use proptest_arbitrary_interop::arb;
     use rand::prelude::*;
@@ -1109,21 +1093,4 @@ mod tests {
     ) {
         let _verdict = fri.verify(&mut proof_stream);
     }
-
-    #[proptest]
-    fn polynomial_evaluation_and_barycentric_evaluation_are_equivalent(
-        #[strategy(1_usize..13)] _log_num_coefficients: usize,
-        #[strategy(1_usize..6)] log_expansion_factor: usize,
-        #[strategy(vec(arb(), 1 << #_log_num_coefficients))] coefficients: Vec<XFieldElement>,
-        #[strategy(arb())] indeterminate: XFieldElement,
-    ) {
-        let domain_len = coefficients.len() * (1 << log_expansion_factor);
-        let domain = ArithmeticDomain::of_length(domain_len).unwrap();
-        let polynomial = Polynomial::from(&coefficients);
-        let codeword = domain.evaluate(&polynomial);
-        prop_assert_eq!(
-            polynomial.evaluate(indeterminate),
-            barycentric_evaluate(&codeword, indeterminate)
-        );
-    }
 }