use a struct for descriptor pointer

ssz-rs/src/merkleization/compact_multiproofs.rs

@@ -90,11 +90,16 @@ fn compute_bits_from_proof_descriptor(descriptor: &[u8]) -> Result<Vec<bool>, Er
  Ok(bits)
 }
 
+struct Pointer {
+ bit_index: usize,
+ node_index: usize,
+}
+
 fn calculate_compact_multi_merkle_root(nodes: &[Node], descriptor: &[u8]) -> Result<Node, Error> {
  let bits = compute_bits_from_proof_descriptor(descriptor)?;
- let mut ptr = [0, 0]; // [bit_index, node_index]
+ let mut ptr = Pointer { bit_index: 0, node_index: 0 };
  let root = calculate_compact_multi_merkle_root_inner(nodes, &bits, &mut ptr)?;
- if ptr[0] != bits.len() || ptr[1] != nodes.len() {
+ if ptr.bit_index != bits.len() || ptr.node_index != nodes.len() {
  Err(Error::InvalidProof)
  } else {
  Ok(root)
@@ -104,13 +109,13 @@ fn calculate_compact_multi_merkle_root(nodes: &[Node], descriptor: &[u8]) -> Res
 fn calculate_compact_multi_merkle_root_inner(
  nodes: &[Node],
  bits: &[bool],
- ptr: &mut [usize; 2],
+ ptr: &mut Pointer,
 ) -> Result<Node, Error> {
- let bit = bits[ptr[0]];
- ptr[0] += 1;
+ let bit = bits[ptr.bit_index];
+ ptr.bit_index += 1;
  if bit {
- let node = nodes[ptr[1]];
- ptr[1] += 1;
+ let node = nodes[ptr.node_index];
+ ptr.node_index += 1;
  Ok(node)
  } else {
  let left = calculate_compact_multi_merkle_root_inner(nodes, bits, ptr)?;