allocating batch inverse

crates/prover/src/constraint_framework/logup.rs

@@ -11,10 +11,10 @@ use crate::core::backend::simd::qm31::PackedSecureField;
 use crate::core::backend::simd::SimdBackend;
 use crate::core::backend::Column;
 use crate::core::channel::Channel;
+use crate::core::fields::batch_inverse_in_place;
 use crate::core::fields::m31::BaseField;
 use crate::core::fields::qm31::SecureField;
 use crate::core::fields::secure_column::SecureColumnByCoords;
-use crate::core::fields::FieldExpOps;
 use crate::core::lookups::utils::Fraction;
 use crate::core::poly::circle::{CanonicCoset, CircleEvaluation};
 use crate::core::poly::BitReversedOrder;
@@ -259,7 +259,7 @@ impl LogupColGenerator<'_> {
 
     /// Finalizes generating the column.
     pub fn finalize_col(mut self) {
-        FieldExpOps::batch_inverse(&self.gen.denom.data, &mut self.gen.denom_inv.data);
+        batch_inverse_in_place(&self.gen.denom.data, &mut self.gen.denom_inv.data);
 
         for vec_row in 0..(1 << (self.gen.log_size - LOG_N_LANES)) {
             unsafe {

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

@@ -7,7 +7,7 @@ use crate::core::circle::{CirclePoint, Coset};
 use crate::core::fft::{butterfly, ibutterfly};
 use crate::core::fields::m31::BaseField;
 use crate::core::fields::qm31::SecureField;
-use crate::core::fields::{ExtensionOf, FieldExpOps};
+use crate::core::fields::{batch_inverse_in_place, ExtensionOf};
 use crate::core::poly::circle::{
     CanonicCoset, CircleDomain, CircleEvaluation, CirclePoly, PolyOps,
 };
@@ -172,7 +172,7 @@ impl PolyOps for CpuBackend {
             .array_chunks::<CHUNK_SIZE>()
             .zip(itwiddles.array_chunks_mut::<CHUNK_SIZE>())
             .for_each(|(src, dst)| {
-                BaseField::batch_inverse(src, dst);
+                batch_inverse_in_place(src, dst);
             });
 
         TwiddleTree {

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

@@ -90,7 +90,7 @@ mod tests {
     use crate::core::backend::cpu::bit_reverse;
     use crate::core::backend::Column;
     use crate::core::fields::qm31::QM31;
-    use crate::core::fields::FieldExpOps;
+    use crate::core::fields::{batch_inverse_in_place, FieldExpOps};
 
     #[test]
     fn bit_reverse_works() {
@@ -106,14 +106,15 @@ mod tests {
         bit_reverse(&mut data);
     }
 
+    // TODO(Ohad): remove.
     #[test]
-    fn batch_inverse_test() {
+    fn batch_inverse_in_place_test() {
         let mut rng = SmallRng::seed_from_u64(0);
         let column = rng.gen::<[QM31; 16]>().to_vec();
         let expected = column.iter().map(|e| e.inverse()).collect_vec();
         let mut dst = Vec::zeros(column.len());
 
-        FieldExpOps::batch_inverse(&column, &mut dst);
+        batch_inverse_in_place(&column, &mut dst);
 
         assert_eq!(expected, dst);
     }

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

@@ -132,10 +132,7 @@ fn denominator_inverses(
         denominators.push((prx - domain_point.x) * piy - (pry - domain_point.y) * pix);
     }
 
-    let mut denominator_inverses = vec![CM31::zero(); denominators.len()];
-    CM31::batch_inverse(&denominators, &mut denominator_inverses);
-
-    denominator_inverses
+    CM31::batch_inverse(&denominators)
 }
 
 pub fn quotient_constants(

crates/prover/src/core/backend/simd/circle.rs

@@ -96,8 +96,7 @@ impl SimdBackend {
             denominators.push(denominators[i - 1] * mappings[i]);
         }
 
-        let mut denom_inverses = vec![F::zero(); denominators.len()];
-        F::batch_inverse(&denominators, &mut denom_inverses);
+        let denom_inverses = F::batch_inverse(&denominators);
 
         let mut steps = vec![mappings[0]];
 
@@ -311,8 +310,7 @@ impl PolyOps for SimdBackend {
             remaining_twiddles.try_into().unwrap(),
         ));
 
-        let mut itwiddles = unsafe { BaseColumn::uninitialized(root_coset.size()) }.data;
-        PackedBaseField::batch_inverse(&twiddles, &mut itwiddles);
+        let itwiddles = PackedBaseField::batch_inverse(&twiddles);
 
         let dbl_twiddles = twiddles
             .into_iter()

crates/prover/src/core/backend/simd/quotients.rs

@@ -12,7 +12,7 @@ use super::qm31::PackedSecureField;
 use super::SimdBackend;
 use crate::core::backend::cpu::bit_reverse;
 use crate::core::backend::cpu::quotients::{batch_random_coeffs, column_line_coeffs};
-use crate::core::backend::{Column, CpuBackend};
+use crate::core::backend::CpuBackend;
 use crate::core::fields::m31::BaseField;
 use crate::core::fields::qm31::SecureField;
 use crate::core::fields::secure_column::{SecureColumnByCoords, SECURE_EXTENSION_DEGREE};
@@ -251,15 +251,9 @@ fn denominator_inverses(
         })
         .collect();
 
-    let mut flat_denominator_inverses =
-        unsafe { CM31Column::uninitialized(flat_denominators.len()) };
-    FieldExpOps::batch_inverse(
-        &flat_denominators.data,
-        &mut flat_denominator_inverses.data[..],
-    );
+    let flat_denominator_inverses = PackedCM31::batch_inverse(&flat_denominators.data);
 
     flat_denominator_inverses
-        .data
         .chunks(domain.size() / N_LANES)
         .map(|denominator_inverses| denominator_inverses.iter().copied().collect())
         .collect()

crates/prover/src/core/backend/simd/very_packed_m31.rs

@@ -9,7 +9,7 @@ use super::qm31::PackedQM31;
 use crate::core::fields::cm31::CM31;
 use crate::core::fields::m31::M31;
 use crate::core::fields::qm31::QM31;
-use crate::core::fields::FieldExpOps;
+use crate::core::fields::{batch_inverse_in_place, FieldExpOps};
 
 pub const LOG_N_VERY_PACKED_ELEMS: u32 = 1;
 pub const N_VERY_PACKED_ELEMS: usize = 1 << LOG_N_VERY_PACKED_ELEMS;
@@ -247,7 +247,7 @@ impl<A: One + Copy, const N: usize> One for Vectorized<A, N> {
 impl<A: FieldExpOps + Zero + Copy, const N: usize> FieldExpOps for Vectorized<A, N> {
     fn inverse(&self) -> Self {
         let mut dst = [A::zero(); N];
-        A::batch_inverse(&self.0, &mut dst);
+        batch_inverse_in_place(&self.0, &mut dst);
         dst.into()
     }
 }

crates/prover/src/core/fields/mod.rs

@@ -30,37 +30,8 @@ pub trait FieldExpOps: Mul<Output = Self> + MulAssign + Sized + One + Clone {
 
     fn inverse(&self) -> Self;
 
-    /// Inverts a batch of elements using Montgomery's trick.
-    fn batch_inverse(column: &[Self], dst: &mut [Self]) {
-        const WIDTH: usize = 4;
-        let n = column.len();
-        debug_assert!(dst.len() >= n);
-
-        if n <= WIDTH || n % WIDTH != 0 {
-            batch_inverse_classic(column, dst);
-            return;
-        }
-
-        // First pass. Compute 'WIDTH' cumulative products in an interleaving fashion, reducing
-        // instruction dependency and allowing better pipelining.
-        let mut cum_prod: [Self; WIDTH] = std::array::from_fn(|_| Self::one());
-        dst[..WIDTH].clone_from_slice(&cum_prod);
-        for i in 0..n {
-            cum_prod[i % WIDTH] *= column[i].clone();
-            dst[i] = cum_prod[i % WIDTH].clone();
-        }
-
-        // Inverse cumulative products.
-        // Use classic batch inversion.
-        let mut tail_inverses: [Self; WIDTH] = std::array::from_fn(|_| Self::one());
-        batch_inverse_classic(&dst[n - WIDTH..], &mut tail_inverses);
-
-        // Second pass.
-        for i in (WIDTH..n).rev() {
-            dst[i] = dst[i - WIDTH].clone() * tail_inverses[i % WIDTH].clone();
-            tail_inverses[i % WIDTH] *= column[i].clone();
-        }
-        dst[0..WIDTH].clone_from_slice(&tail_inverses);
+    fn batch_inverse(column: &[Self]) -> Vec<Self> {
+        batch_inverse(column)
     }
 }
 
@@ -91,6 +62,46 @@ fn batch_inverse_classic<T: FieldExpOps>(column: &[T], dst: &mut [T]) {
     dst[0] = curr_inverse;
 }
 
+/// Inverts a batch of elements using Montgomery's trick.
+pub fn batch_inverse_in_place<F: FieldExpOps>(column: &[F], dst: &mut [F]) {
+    const WIDTH: usize = 4;
+    let n = column.len();
+    debug_assert!(dst.len() >= n);
+
+    if n <= WIDTH || n % WIDTH != 0 {
+        batch_inverse_classic(column, dst);
+        return;
+    }
+
+    // First pass. Compute 'WIDTH' cumulative products in an interleaving fashion, reducing
+    // instruction dependency and allowing better pipelining.
+    let mut cum_prod: [F; WIDTH] = std::array::from_fn(|_| F::one());
+    dst[..WIDTH].clone_from_slice(&cum_prod);
+    for i in 0..n {
+        cum_prod[i % WIDTH] *= column[i].clone();
+        dst[i] = cum_prod[i % WIDTH].clone();
+    }
+
+    // Inverse cumulative products.
+    // Use classic batch inversion.
+    let mut tail_inverses: [F; WIDTH] = std::array::from_fn(|_| F::one());
+    batch_inverse_classic(&dst[n - WIDTH..], &mut tail_inverses);
+
+    // Second pass.
+    for i in (WIDTH..n).rev() {
+        dst[i] = dst[i - WIDTH].clone() * tail_inverses[i % WIDTH].clone();
+        tail_inverses[i % WIDTH] *= column[i].clone();
+    }
+    dst[0..WIDTH].clone_from_slice(&tail_inverses);
+}
+
+// TODO(Ohad): chunks, parallelize.
+pub fn batch_inverse<F: FieldExpOps>(column: &[F]) -> Vec<F> {
+    let mut dst = vec![unsafe { std::mem::zeroed() }; column.len()];
+    batch_inverse_in_place(column, &mut dst);
+    dst
+}
+
 pub trait Field:
     NumAssign
     + Neg<Output = Self>
@@ -460,19 +471,19 @@ mod tests {
     use rand::rngs::SmallRng;
     use rand::{Rng, SeedableRng};
 
+    use super::batch_inverse_in_place;
+    use crate::core::fields::batch_inverse;
     use crate::core::fields::m31::M31;
-    use crate::core::fields::FieldExpOps;
 
     #[test]
-    fn test_slice_batch_inverse() {
+    fn test_batch_inverse() {
         let mut rng = SmallRng::seed_from_u64(0);
         let elements: [M31; 16] = rng.gen();
         let expected = elements.iter().map(|e| e.inverse()).collect::<Vec<_>>();
-        let mut dst = [M31::zero(); 16];
 
-        M31::batch_inverse(&elements, &mut dst);
+        let actual = batch_inverse(&elements);
 
-        assert_eq!(expected, dst);
+        assert_eq!(expected, actual);
     }
 
     #[test]
@@ -482,6 +493,6 @@ mod tests {
         let elements: [M31; 16] = rng.gen();
         let mut dst = [M31::zero(); 15];
 
-        M31::batch_inverse(&elements, &mut dst);
+        batch_inverse_in_place(&elements, &mut dst);
     }
 }

crates/prover/src/examples/xor/gkr_lookups/mle_eval.rs

@@ -688,8 +688,7 @@ fn eval_step_selector(coset: Coset, log_step: u32, p: CirclePoint<SecureField>)
     vanish_at_log_step.reverse();
     // We only need the first `log_step` many values.
     vanish_at_log_step.truncate(log_step as usize);
-    let mut vanish_at_log_step_inv = vec![SecureField::zero(); vanish_at_log_step.len()];
-    SecureField::batch_inverse(&vanish_at_log_step, &mut vanish_at_log_step_inv);
+    let vanish_at_log_step_inv = SecureField::batch_inverse(&vanish_at_log_step);
 
     let half_coset_selector_dbl = (vanish_at_log_step[0] * vanish_at_log_step_inv[1]).square();
     let vanish_substep_inv_sum = vanish_at_log_step_inv[1..].iter().sum::<SecureField>();