From 98f9bab876856bcff9ded92a06ac7e38cc50320d Mon Sep 17 00:00:00 2001
From: Thor Kamphefner <thorck@pm.me>
Date: Mon, 10 Jul 2023 17:26:39 -0700
Subject: [PATCH] lint powers_of

---
 halo2_proofs/src/protostar/error_check.rs | 28 ++++++++++++++---------
 halo2_proofs/src/protostar/shuffle.rs     |  2 ++
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/halo2_proofs/src/protostar/error_check.rs b/halo2_proofs/src/protostar/error_check.rs
index 3c05dfa0..a69a9d60 100644
--- a/halo2_proofs/src/protostar/error_check.rs
+++ b/halo2_proofs/src/protostar/error_check.rs
@@ -436,15 +436,21 @@ pub fn evaluated_challenge_powers<F: Field>(
 }
 
 /// Computes [1, v, v^2, ..., v^max_degee]
-fn powers_of<F: Field>(v: &F, max_degee: usize) -> Vec<F> {
-    let mut powers = Vec::with_capacity(max_degee + 1);
-    let mut acc = F::ONE;
-    powers.push(acc);
-
-    // we need max_degee + 1 since we include v^0 = 1
-    for _i in 1..max_degee + 1 {
-        acc *= v;
-        powers.push(acc);
-    }
-    powers
+fn powers_of<F: Field>(v: &F, max_degree: usize) -> Vec<F> {
+    std::iter::successors(Some(F::ONE), |&n| Some(n * v))
+        // we need max_degee + 1 since we include v^0 = 1
+        .take(max_degree + 1)
+        .collect()
 }
+
+#[cfg(test)]
+mod test{
+    use super::*;
+    use crate::{halo2curves::pasta::Fp, plonk::sealed::SealedPhase};
+    #[test]
+    fn test_powers_of(){
+        let v = Fp::from(2u64);
+        let expect: Vec<Fp> = [1,2,4,8,16,32].into_iter().map(Fp::from).collect();
+        assert_eq!(expect, powers_of(&v, 5));
+    }
+}
\ No newline at end of file
diff --git a/halo2_proofs/src/protostar/shuffle.rs b/halo2_proofs/src/protostar/shuffle.rs
index 133cb3dd..f53e38f7 100644
--- a/halo2_proofs/src/protostar/shuffle.rs
+++ b/halo2_proofs/src/protostar/shuffle.rs
@@ -21,10 +21,12 @@ use ff::{BatchInvert, FromUniformBytes};
 use rand_core::{OsRng, RngCore};
 use std::iter::{self, zip};
 
+/// generate a random 2d array of field elements of size W x H
 fn rand_2d_array<F: Field, R: RngCore, const W: usize, const H: usize>(rng: &mut R) -> [[F; H]; W] {
     [(); W].map(|_| [(); H].map(|_| F::random(&mut *rng)))
 }
 
+/// randomly permute the columns 2d array `original`
 fn shuffled<F: Field, R: RngCore, const W: usize, const H: usize>(
     original: [[F; H]; W],
     rng: &mut R,