From 92a7e20d3019bbd020bdc5dcd8fd96f56e31a8f7 Mon Sep 17 00:00:00 2001
From: therealyingtong <yingtong@z.cash>
Date: Thu, 12 Aug 2021 20:52:37 +0800
Subject: [PATCH] Remove sinsemilla_s_generators() function.

Co-authored-by: Jack Grigg <jack@electriccoin.co>
---
 src/primitives/sinsemilla.rs           |  5 +++--
 src/primitives/sinsemilla/constants.rs | 27 ++++++++++----------------
 2 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/src/primitives/sinsemilla.rs b/src/primitives/sinsemilla.rs
index 49c20ab8..f08e5ff3 100644
--- a/src/primitives/sinsemilla.rs
+++ b/src/primitives/sinsemilla.rs
@@ -13,7 +13,7 @@ use self::addition::IncompletePoint;
 mod constants;
 mod sinsemilla_s;
 pub use constants::*;
-pub use sinsemilla_s::*;
+pub(crate) use sinsemilla_s::*;
 
 pub(crate) fn lebs2ip_k(bits: &[bool]) -> u32 {
     assert!(bits.len() == K);
@@ -120,7 +120,8 @@ impl HashDomain {
             .chunks(K)
             .fold(IncompletePoint::from(self.Q), |acc, chunk| {
                 let (S_x, S_y) = SINSEMILLA_S[lebs2ip_k(chunk) as usize];
-                acc + pallas::Affine::from_xy(S_x, S_y).unwrap().to_curve() + acc
+                let S_chunk = pallas::Affine::from_xy(S_x, S_y).unwrap().to_curve();
+                (acc + S_chunk) + acc
             })
     }
 
diff --git a/src/primitives/sinsemilla/constants.rs b/src/primitives/sinsemilla/constants.rs
index 5593aab2..47f3535f 100644
--- a/src/primitives/sinsemilla/constants.rs
+++ b/src/primitives/sinsemilla/constants.rs
@@ -1,7 +1,4 @@
 //! Sinsemilla generators
-use group::Curve;
-use halo2::arithmetic::{CurveAffine, CurveExt};
-use pasta_curves::pallas;
 
 /// Number of bits of each message piece in $\mathsf{SinsemillaHashToPoint}$
 pub const K: usize = 10;
@@ -62,15 +59,6 @@ pub const Q_MERKLE_CRH: ([u8; 32], [u8; 32]) = (
 /// SWU hash-to-curve personalization for Sinsemilla $S$ generators.
 pub const S_PERSONALIZATION: &str = "z.cash:SinsemillaS";
 
-/// Creates the Sinsemilla S generators used in each round of the Sinsemilla hash
-pub fn sinsemilla_s_generators() -> impl Iterator<Item = (pallas::Base, pallas::Base)> {
-    let hasher = pallas::Point::hash_to_curve(S_PERSONALIZATION);
-    (0..(1u32 << K)).map(move |j| {
-        let point = hasher(&j.to_le_bytes()).to_affine().coordinates().unwrap();
-        (*point.x(), *point.y())
-    })
-}
-
 #[cfg(test)]
 mod tests {
     use super::super::{CommitDomain, HashDomain};
@@ -79,16 +67,21 @@ mod tests {
         COMMIT_IVK_PERSONALIZATION, MERKLE_CRH_PERSONALIZATION, NOTE_COMMITMENT_PERSONALIZATION,
     };
     use group::Curve;
-    use halo2::arithmetic::FieldExt;
+    use halo2::arithmetic::{CurveAffine, CurveExt, FieldExt};
     use halo2::pasta::pallas;
 
     #[test]
     fn sinsemilla_s() {
         use super::super::sinsemilla_s::SINSEMILLA_S;
-        let sinsemilla_s: Vec<_> = sinsemilla_s_generators().collect();
-        assert_eq!(sinsemilla_s.len(), SINSEMILLA_S.len());
-        for (expected, actual) in sinsemilla_s.iter().zip(&SINSEMILLA_S[..]) {
-            assert_eq!(expected, actual);
+        let hasher = pallas::Point::hash_to_curve(S_PERSONALIZATION);
+
+        for j in 0..(1u32 << K) {
+            let computed = {
+                let point = hasher(&j.to_le_bytes()).to_affine().coordinates().unwrap();
+                (*point.x(), *point.y())
+            };
+            let actual = SINSEMILLA_S[j as usize];
+            assert_eq!(computed, actual);
         }
     }