Simplify `gen_const_array` implementation

Also includes a performance improvement to `i2lebsp_k`.

src/constants/util.rs

@@ -42,15 +42,11 @@ pub fn evaluate<C: CurveAffine>(x: u8, coeffs: &[C::Base]) -> C::Base {
 
 /// Takes in an FnMut closure and returns a constant-length array with elements of
 /// type `Output`.
-pub fn gen_const_array<Input, Output: Copy + Default, const LEN: usize>(
-    mut input: Input,
-    mut closure: impl FnMut(&mut Input, usize) -> Output,
+pub fn gen_const_array<Output: Copy + Default, const LEN: usize>(
+    mut closure: impl FnMut(usize) -> Output,
 ) -> [Output; LEN] {
     let mut ret: [Output; LEN] = [Default::default(); LEN];
-    for (bit, val) in ret
-        .iter_mut()
-        .zip((0..LEN).map(|idx| closure(&mut input, idx)))
-    {
+    for (bit, val) in ret.iter_mut().zip((0..LEN).map(|idx| closure(idx))) {
         *bit = val;
     }
     ret

src/primitives/sinsemilla.rs

@@ -25,9 +25,7 @@ fn lebs2ip_k(bits: &[bool]) -> u32 {
 /// up to `2^K` - 1.
 pub fn i2lebsp_k(int: usize) -> [bool; K] {
     assert!(int < (1 << K));
-    gen_const_array(int, |int: &mut usize, mask: usize| {
-        ((*int & (1 << mask)) >> mask) == 1
-    })
+    gen_const_array(|mask: usize| (int & (1 << mask)) != 0)
 }
 
 /// Pads the given iterator (which MUST have length $\leq K * C$) with zero-bits to a

src/tree.rs

@@ -29,14 +29,10 @@ pub struct MerklePath {
 
 impl MerklePath {
     /// Generates a dummy Merkle path for use in dummy spent notes.
-    pub(crate) fn dummy(rng: &mut impl RngCore) -> Self {
-        fn dummy_inner(rng: &mut impl RngCore, _idx: usize) -> pallas::Base {
-            pallas::Base::random(rng)
-        }
-
+    pub(crate) fn dummy(mut rng: &mut impl RngCore) -> Self {
         MerklePath {
             position: rng.next_u32(),
-            auth_path: gen_const_array(rng, dummy_inner),
+            auth_path: gen_const_array(|_| pallas::Base::random(&mut rng)),
         }
     }