Add secure powers generation for simd

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

@@ -1,5 +1,11 @@
 use std::simd::Swizzle;
 
+use num_traits::One;
+
+use crate::core::backend::simd::m31::N_LANES;
+use crate::core::backend::simd::qm31::PackedSecureField;
+use crate::core::fields::qm31::SecureField;
+
 /// Used with [`Swizzle::concat_swizzle`] to interleave the even values of two vectors.
 pub struct InterleaveEvens;
 
@@ -51,11 +57,51 @@ impl<T> UnsafeConst<T> {
 unsafe impl<T> Send for UnsafeConst<T> {}
 unsafe impl<T> Sync for UnsafeConst<T> {}
 
+// TODO(Gali): Remove #[allow(dead_code)].
+#[allow(dead_code)]
+pub fn generate_secure_powers_for_simd(felt: SecureField, n_powers: usize) -> Vec<SecureField> {
+    let step_arr: [SecureField; N_LANES] = (0..N_LANES)
+        .scan(SecureField::one(), |acc, _| {
+            let res = *acc;
+            *acc *= felt;
+            Some(res)
+        })
+        .collect::<Vec<SecureField>>()
+        .try_into()
+        .expect("Failed generating secure powers.");
+    let step_packed_felt = PackedSecureField::from_array(step_arr);
+
+    let mut base_felt = SecureField::one();
+    let step_felt = step_arr[N_LANES - 1] * felt;
+
+    let mut packed_powers_vec = Vec::new();
+    let mut curr_power: usize = 0;
+
+    while curr_power < n_powers {
+        let base_packed_felt = PackedSecureField::from_array([base_felt; N_LANES]);
+        packed_powers_vec.push(base_packed_felt * step_packed_felt);
+        base_felt *= step_felt;
+        curr_power += N_LANES;
+    }
+
+    let powers_vec: Vec<SecureField> = packed_powers_vec
+        .iter()
+        .flat_map(|x| x.to_array().to_vec())
+        .collect();
+
+    powers_vec[0..n_powers].to_vec()
+}
+
 #[cfg(test)]
 mod tests {
     use std::simd::{u32x4, Swizzle};
 
-    use super::{InterleaveEvens, InterleaveOdds};
+    use num_traits::One;
+
+    use super::{generate_secure_powers_for_simd, InterleaveEvens, InterleaveOdds};
+    use crate::core::fields::qm31::SecureField;
+    use crate::core::fields::FieldExpOps;
+    use crate::qm31;
 
     #[test]
     fn interleave_evens() {
@@ -76,4 +122,27 @@ mod tests {
 
         assert_eq!(res, u32x4::from_array([1, 5, 3, 7]));
     }
+
+    #[test]
+    fn generate_secure_powers_works() {
+        let felt = qm31!(1, 2, 3, 4);
+        let n_powers = 10;
+
+        let powers = generate_secure_powers_for_simd(felt, n_powers);
+
+        assert_eq!(powers.len(), n_powers);
+        assert_eq!(powers[0], SecureField::one());
+        assert_eq!(powers[1], felt);
+        assert_eq!(powers[7], felt.pow(7));
+    }
+
+    #[test]
+    fn generate_empty_secure_powers_works() {
+        let felt = qm31!(1, 2, 3, 4);
+        let max_log_size = 0;
+
+        let powers = generate_secure_powers_for_simd(felt, max_log_size);
+
+        assert_eq!(powers, vec![]);
+    }
 }