chore(merkle_root): move function into lib.rs

Signed-off-by: Johns Beharry <johns@peakshift.com>

eth2/utils/hashing/src/lib.rs

@@ -8,6 +8,33 @@ pub fn hash(input: &[u8]) -> Vec<u8> {
     result
 }
 
+/// Generate Merkle Root
+/// 
+/// Outputs a `Vec<u8>` byte array of the merkle root given a set of leaf node values.
+/// Expects leaf nodes to already be hashed.
+pub fn merkle_root(values: &[Vec<u8>]) -> Vec<u8> {
+    let values_len = values.len();
+    
+    // vector to store hashes
+    // filled with 0 as placeholders
+    let mut o: Vec<Vec<u8>> = vec![vec![0]; values_len];
+
+    // append values to the end
+    o.append(&mut values.to_vec());
+
+    // traverse backwards as values are at the end
+    // then fill placeholders with a hash of two leaf nodes
+    for i in (0..values_len).rev() {
+        let mut current_value: Vec<u8> = o[i * 2].clone();
+        current_value.append(&mut o[i * 2 + 1].clone());
+
+        o[i] = hash(&current_value[..]);
+    }
+
+    // the root hash will be at index 1
+    o[1].clone()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -25,4 +52,36 @@ mod tests {
         ];
         assert_eq!(expected, output.as_slice());
     }
+
+    #[test]
+    fn test_merkle_root() {
+        // hash the leaf nodes
+        let mut input = vec![
+            hash("a".as_bytes()),
+            hash("b".as_bytes()),
+            hash("c".as_bytes()),
+            hash("d".as_bytes()),
+        ];
+
+        // generate a merkle tree and return the root
+        let output = merkle_root(&input[..]);
+
+        // create merkle root manually
+        let mut leaf_1_2: Vec<u8> = input[0].clone(); // a
+        leaf_1_2.append(&mut input[1].clone()); // b
+
+        let mut leaf_3_4: Vec<u8> = input[2].clone(); // c
+        leaf_3_4.append(&mut input[3].clone()); // d
+
+        let node_1 = hash(&leaf_1_2[..]);
+        let node_2 = hash(&leaf_3_4[..]);
+
+        let mut root: Vec<u8> = node_1.clone(); // ab
+        root.append(&mut node_2.clone()); // cd
+
+        let expected = hash(&root[..]);
+
+        assert_eq!(&expected[..], output.as_slice());
+
+    }
 }

eth2/utils/hashing/src/merkle_root.rs

@@ -1,41 +0,0 @@
-use crate::hash;
-
-pub fn merkle_root(values: &[Vec<u8>]) -> Vec<u8> {
-    let values_len = values.len();
-    let mut o: Vec<Vec<u8>> = vec![vec![0]; values_len];
-
-    o.append(&mut values.to_vec());
-
-    for i in (0..values_len).rev() {
-        let mut current_value: Vec<u8> = o[i * 2].clone();
-        current_value.append(&mut o[i * 2 + 1].clone());
-
-        o[i] = hash(&current_value[..]);
-    }
-
-    o[1].clone()
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_merkle_root() {
-        let input = vec![
-            "a".as_bytes().to_vec(),
-            "b".as_bytes().to_vec(),
-            "c".as_bytes().to_vec(),
-            "d".as_bytes().to_vec()
-        ];
-
-        let output = merkle_root(&input[..]);
-
-        // merkle root of [[a],[b],[c],[d]]
-        let expected = &[
-            183, 91, 96, 122, 144, 174, 84, 92, 97, 156, 140, 192, 66, 221, 55, 229,
-            234, 48, 118, 7, 61, 207, 39, 125, 150, 32, 94, 90, 19, 88, 122, 163,
-        ];
-        assert_eq!(expected, output.as_slice());
-    }
-}