Implement GkrOps for SIMD backend

crates/prover/src/core/backend/cpu/lookups/gkr.rs

@@ -234,7 +234,7 @@ fn eval_logup_singles_sum(
 /// Returns evaluations `eq(x, y) * v` for all `x` in `{0, 1}^n`.
 ///
 /// Evaluations are returned in bit-reversed order.
-fn gen_eq_evals(y: &[SecureField], v: SecureField) -> Vec<SecureField> {
+pub fn gen_eq_evals(y: &[SecureField], v: SecureField) -> Vec<SecureField> {
     let mut evals = Vec::with_capacity(1 << y.len());
     evals.push(v);
 
@@ -328,7 +328,7 @@ mod tests {
         let eq_evals = CpuBackend::gen_eq_evals(&y, two);
 
         assert_eq!(
-            **eq_evals,
+            *eq_evals,
             [
                 eq(&[zero, zero], &y) * two,
                 eq(&[zero, one], &y) * two,

crates/prover/src/core/backend/cpu/lookups/mod.rs

@@ -1,2 +1,2 @@
-mod gkr;
+pub mod gkr;
 mod mle;

crates/prover/src/core/backend/cpu/mod.rs

@@ -2,7 +2,7 @@ mod accumulation;
 mod blake2s;
 mod circle;
 mod fri;
-mod lookups;
+pub mod lookups;
 pub mod quotients;
 
 use std::fmt::Debug;

crates/prover/src/core/backend/simd/lookups/gkr.rs

@@ -0,0 +1,90 @@
+use std::iter::zip;
+
+use crate::core::backend::cpu::lookups::gkr::gen_eq_evals as cpu_gen_eq_evals;
+use crate::core::backend::simd::column::SecureFieldVec;
+use crate::core::backend::simd::m31::{LOG_N_LANES, N_LANES};
+use crate::core::backend::simd::qm31::PackedSecureField;
+use crate::core::backend::simd::SimdBackend;
+use crate::core::backend::Column;
+use crate::core::fields::qm31::SecureField;
+use crate::core::lookups::gkr_prover::{GkrMultivariatePolyOracle, GkrOps, Layer};
+use crate::core::lookups::mle::Mle;
+use crate::core::lookups::utils::UnivariatePoly;
+
+impl GkrOps for SimdBackend {
+    #[allow(clippy::uninit_vec)]
+    fn gen_eq_evals(y: &[SecureField], v: SecureField) -> Mle<Self, SecureField> {
+        if y.len() < LOG_N_LANES as usize {
+            return Mle::new(cpu_gen_eq_evals(y, v).into_iter().collect());
+        }
+
+        // Start DP with CPU backend to avoid dealing with instances smaller than a SIMD vector.
+        let (y_last_chunk, y_rem) = y.split_last_chunk::<{ LOG_N_LANES as usize }>().unwrap();
+        let initial = SecureFieldVec::from_iter(cpu_gen_eq_evals(y_last_chunk, v));
+        assert_eq!(initial.len(), N_LANES);
+
+        let packed_len = 1 << y_rem.len();
+        let mut data = initial.data;
+
+        data.reserve(packed_len - data.len());
+        unsafe { data.set_len(packed_len) };
+
+        for (i, &y_j) in y_rem.iter().rev().enumerate() {
+            let packed_y_j = PackedSecureField::broadcast(y_j);
+
+            let (lhs_evals, rhs_evals) = data.split_at_mut(1 << i);
+
+            for (lhs, rhs) in zip(lhs_evals, rhs_evals) {
+                // Equivalent to:
+                // `rhs = eq(1, y_j) * lhs`,
+                // `lhs = eq(0, y_j) * lhs`
+                *rhs = *lhs * packed_y_j;
+                *lhs -= *rhs;
+            }
+        }
+
+        let length = packed_len * N_LANES;
+        Mle::new(SecureFieldVec { data, length })
+    }
+
+    fn next_layer(_layer: &Layer<Self>) -> Layer<Self> {
+        todo!()
+    }
+
+    fn sum_as_poly_in_first_variable(
+        _h: &GkrMultivariatePolyOracle<'_, Self>,
+        _claim: SecureField,
+    ) -> UnivariatePoly<SecureField> {
+        todo!()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::core::backend::simd::SimdBackend;
+    use crate::core::backend::{Column, CpuBackend};
+    use crate::core::fields::m31::BaseField;
+    use crate::core::lookups::gkr_prover::GkrOps;
+
+    #[test]
+    fn gen_eq_evals_matches_cpu() {
+        let two = BaseField::from(2).into();
+        let y = [7, 3, 5, 6, 1, 1, 9].map(|v| BaseField::from(v).into());
+        let eq_evals_cpu = CpuBackend::gen_eq_evals(&y, two);
+
+        let eq_evals_simd = SimdBackend::gen_eq_evals(&y, two);
+
+        assert_eq!(eq_evals_simd.to_cpu(), *eq_evals_cpu);
+    }
+
+    #[test]
+    fn gen_eq_evals_with_small_assignment_matches_cpu() {
+        let two = BaseField::from(2).into();
+        let y = [7, 3, 5].map(|v| BaseField::from(v).into());
+        let eq_evals_cpu = CpuBackend::gen_eq_evals(&y, two);
+
+        let eq_evals_simd = SimdBackend::gen_eq_evals(&y, two);
+
+        assert_eq!(eq_evals_simd.to_cpu(), *eq_evals_cpu);
+    }
+}

crates/prover/src/core/backend/simd/lookups/mod.rs

@@ -1 +1,2 @@
+mod gkr;
 mod mle;

crates/prover/src/lib.rs

@@ -8,6 +8,7 @@
     stdsimd,
     get_many_mut,
     int_roundings,
+    slice_first_last_chunk,
     slice_flatten,
     assert_matches,
     portable_simd