Factoring in mmr leaf count function

chain/src/sumtree.rs

@@ -468,9 +468,8 @@ impl<'a> Extension<'a> {
 
 		// rewind the kernel file store, the position is the number of kernels
 		// multiplied by their size
-		// the number of kernels is the number of leaves in the MMR, which is the
+		// the number of kernels is the number of leaves in the MMR
-		// sum of the number of leaf nodes under each peak in the MMR
+		let pos = pmmr::n_leaves(kern_pos_rew);
-		let pos: u64 = pmmr::peaks(kern_pos_rew).iter().map(|n| (1 << n) as u64).sum();
 		self.kernel_file.rewind(pos * (TxKernel::size() as u64));
 
 		Ok(())
@@ -618,9 +617,7 @@ impl<'a> Extension<'a> {
 		// make sure we have the right count of kernels using the MMR, the storage
 		// file may have a few more
 		let mmr_sz = self.kernel_pmmr.unpruned_size();
-		let count: u64 = pmmr::peaks(mmr_sz).iter().map(|n| {
+		let count = pmmr::n_leaves(mmr_sz);
-			(1 << pmmr::bintree_postorder_height(*n)) as u64
-		}).sum();
 
 		let mut kernel_file = File::open(self.kernel_file.path())?;
 		let first: TxKernel = ser::deserialize(&mut kernel_file)?;

core/src/core/pmmr.rs

@@ -661,6 +661,13 @@ pub fn peaks(num: u64) -> Vec<u64> {
 	peaks
 }
 
+/// The number of leaves nodes in a MMR of the provided size. 
+pub fn n_leaves(sz: u64) -> u64 {
+	peaks(sz).iter().map(|n| {
+		(1 << bintree_postorder_height(*n)) as u64
+	}).sum()
+}
+
 /// The height of a node in a full binary tree from its postorder traversal
 /// index. This function is the base on which all others, as well as the MMR,
 /// are built.