Init merkle-mountain-range

The MMR code is copy from https://github.com/nervosnetwork/ckb/pull/1598

src/tests/mod.rs

@@ -0,0 +1,37 @@
+mod test_accumulate_headers;
+mod test_helper;
+mod test_mmr;
+
+use crate::Merge;
+use blake2b_rs::{Blake2b, Blake2bBuilder};
+use bytes::Bytes;
+
+fn new_blake2b() -> Blake2b {
+    Blake2bBuilder::new(32).build()
+}
+
+#[derive(Eq, PartialEq, Clone, Debug, Default)]
+struct NumberHash(pub Bytes);
+impl From<u32> for NumberHash {
+    fn from(num: u32) -> Self {
+        let mut hasher = new_blake2b();
+        let mut hash = [0u8; 32];
+        hasher.update(&num.to_le_bytes());
+        hasher.finalize(&mut hash);
+        NumberHash(hash.to_vec().into())
+    }
+}
+
+struct MergeNumberHash;
+
+impl Merge for MergeNumberHash {
+    type Item = NumberHash;
+    fn merge(lhs: &Self::Item, rhs: &Self::Item) -> Self::Item {
+        let mut hasher = new_blake2b();
+        let mut hash = [0u8; 32];
+        hasher.update(&lhs.0);
+        hasher.update(&rhs.0);
+        hasher.finalize(&mut hash);
+        NumberHash(hash.to_vec().into())
+    }
+}