cache get_shift() and get_leaf_shift() in prune_list (#1495)

* cache shift and leaf_shift values in prune_list for fast lookup later

* rustfmt

* fixup core tests

core/src/core/pmmr.rs

@@ -594,6 +594,9 @@ pub fn peak_map_height(mut pos: u64) -> (u64, u64) {
 /// are built.
 
 pub fn bintree_postorder_height(num: u64) -> u64 {
+	if num == 0 {
+		return 0;
+	}
 	peak_map_height(num - 1).1
 }
 
@@ -669,7 +672,13 @@ pub fn family_branch(pos: u64, last_pos: u64) -> Vec<(u64, u64)> {
 	branch
 }
 
-/// Gets the position of the rightmost node (i.e. leaf) relative to the current
-fn bintree_rightmost(num: u64) -> u64 {
+/// Gets the position of the rightmost node (i.e. leaf) beneath the provided subtree root.
+pub fn bintree_rightmost(num: u64) -> u64 {
 	num - bintree_postorder_height(num)
 }
+
+/// Gets the position of the rightmost node (i.e. leaf) beneath the provided subtree root.
+pub fn bintree_leftmost(num: u64) -> u64 {
+	let height = bintree_postorder_height(num);
+	num + 2 - (2 << height)
+}

core/tests/pmmr.rs

@@ -56,6 +56,32 @@ fn first_100_mmr_heights() {
 	}
 }
 
+// The pos of the rightmost leaf for the provided MMR size (last leaf in subtree).
+#[test]
+fn test_bintree_rightmost() {
+	assert_eq!(pmmr::bintree_rightmost(0), 0);
+	assert_eq!(pmmr::bintree_rightmost(1), 1);
+	assert_eq!(pmmr::bintree_rightmost(2), 2);
+	assert_eq!(pmmr::bintree_rightmost(3), 2);
+	assert_eq!(pmmr::bintree_rightmost(4), 4);
+	assert_eq!(pmmr::bintree_rightmost(5), 5);
+	assert_eq!(pmmr::bintree_rightmost(6), 5);
+	assert_eq!(pmmr::bintree_rightmost(7), 5);
+}
+
+// The pos of the leftmost leaf for the provided MMR size (first leaf in subtree).
+#[test]
+fn test_bintree_leftmost() {
+	assert_eq!(pmmr::bintree_leftmost(0), 0);
+	assert_eq!(pmmr::bintree_leftmost(1), 1);
+	assert_eq!(pmmr::bintree_leftmost(2), 2);
+	assert_eq!(pmmr::bintree_leftmost(3), 1);
+	assert_eq!(pmmr::bintree_leftmost(4), 4);
+	assert_eq!(pmmr::bintree_leftmost(5), 5);
+	assert_eq!(pmmr::bintree_leftmost(6), 4);
+	assert_eq!(pmmr::bintree_leftmost(7), 1);
+}
+
 #[test]
 fn test_n_leaves() {
 	// make sure we handle an empty MMR correctly