use Vec<Vec<u8>> with inner recursion method

tendermint/src/merkle.rs

@@ -10,14 +10,19 @@ pub type Hash = [u8; HASH_SIZE];
 
 /// Compute a simple Merkle root from the arbitrary byte arrays
 pub fn simple_hash_from_byte_slices(byte_slices: Vec<Vec<u8>>) -> Hash {
+    simple_hash_from_byte_slices_inner(byte_slices.as_slice())
+}
+
+// recurse into subtrees
+fn simple_hash_from_byte_slices_inner(byte_slices: &[Vec<u8>]) -> Hash {
     let length = byte_slices.len();
     match length {
         0 => [0; HASH_SIZE],
-        1 => leaf_hash(byte_slices[0].to_vec()),
+        1 => leaf_hash(byte_slices[0].as_slice()),
         _ => {
             let k = get_split_point(length);
-            let left = simple_hash_from_byte_slices(byte_slices[0..k].to_vec());
-            let right = simple_hash_from_byte_slices(byte_slices[k..].to_vec());
+            let left = simple_hash_from_byte_slices_inner(&byte_slices[0..k]);
+            let right = simple_hash_from_byte_slices_inner(&byte_slices[k..]);
             inner_hash(&left, &right)
         }
     }
@@ -34,11 +39,11 @@ fn get_split_point(length: usize) -> usize {
 }
 
 // tmhash(0x00 || leaf)
-fn leaf_hash(bytes: Vec<u8>) -> Hash {
+fn leaf_hash(bytes: &[u8]) -> Hash {
     // make a new array starting with 0 and copy in the bytes
     let mut leaf_bytes = Vec::with_capacity(bytes.len() + 1);
     leaf_bytes.push(0x00);
-    leaf_bytes.extend_from_slice(&bytes);
+    leaf_bytes.extend_from_slice(bytes);
 
     // hash it !
     let digest = Sha256::digest(&leaf_bytes);