Directory Restructure (#1163)

* Move tests -> testing

* Directory restructure

* Update Cargo.toml during restructure

* Update Makefile during restructure

* Fix arbitrary path

consensus/tree_hash/src/lib.rs

@@ -0,0 +1,162 @@
+pub mod impls;
+mod merkle_hasher;
+mod merkleize_padded;
+mod merkleize_standard;
+
+pub use merkle_hasher::{Error, MerkleHasher};
+pub use merkleize_padded::merkleize_padded;
+pub use merkleize_standard::merkleize_standard;
+
+use eth2_hashing::{Context, SHA256};
+use eth2_hashing::{ZERO_HASHES, ZERO_HASHES_MAX_INDEX};
+
+pub const BYTES_PER_CHUNK: usize = 32;
+pub const HASHSIZE: usize = 32;
+pub const MERKLE_HASH_CHUNK: usize = 2 * BYTES_PER_CHUNK;
+
+pub type Hash256 = ethereum_types::H256;
+
+/// Convenience method for `MerkleHasher` which also provides some fast-paths for small trees.
+///
+/// `minimum_leaf_count` will only be used if it is greater than or equal to the minimum number of leaves that can be created from `bytes`.
+pub fn merkle_root(bytes: &[u8], minimum_leaf_count: usize) -> Hash256 {
+    let leaves = std::cmp::max(
+        (bytes.len() + (HASHSIZE - 1)) / HASHSIZE,
+        minimum_leaf_count,
+    );
+
+    if leaves == 0 {
+        // If there are no bytes then the hash is always zero.
+        Hash256::zero()
+    } else if leaves == 1 {
+        // If there is only one leaf, the hash is always those leaf bytes padded out to 32-bytes.
+        let mut hash = [0; HASHSIZE];
+        hash[0..bytes.len()].copy_from_slice(bytes);
+        Hash256::from_slice(&hash)
+    } else if leaves == 2 {
+        // If there are only two leaves (this is common with BLS pubkeys), we can avoid some
+        // overhead with `MerkleHasher` and just do a simple 3-node tree here.
+        let mut leaves = [0; HASHSIZE * 2];
+        leaves[0..bytes.len()].copy_from_slice(bytes);
+
+        let mut context = Context::new(&SHA256);
+        context.update(&leaves);
+        let digest = context.finish();
+
+        Hash256::from_slice(digest.as_ref())
+    } else {
+        // If there are 3 or more leaves, use `MerkleHasher`.
+        let mut hasher = MerkleHasher::with_leaves(leaves);
+        hasher
+            .write(bytes)
+            .expect("the number of leaves is adequate for the number of bytes");
+        hasher
+            .finish()
+            .expect("the number of leaves is adequate for the number of bytes")
+    }
+}
+
+/// Returns the node created by hashing `root` and `length`.
+///
+/// Used in `TreeHash` for inserting the length of a list above it's root.
+pub fn mix_in_length(root: &Hash256, length: usize) -> Hash256 {
+    let usize_len = std::mem::size_of::<usize>();
+
+    let mut length_bytes = [0; BYTES_PER_CHUNK];
+    length_bytes[0..usize_len].copy_from_slice(&length.to_le_bytes());
+
+    Hash256::from_slice(&eth2_hashing::hash32_concat(root.as_bytes(), &length_bytes)[..])
+}
+
+/// Returns a cached padding node for a given height.
+fn get_zero_hash(height: usize) -> &'static [u8] {
+    if height <= ZERO_HASHES_MAX_INDEX {
+        &ZERO_HASHES[height]
+    } else {
+        panic!("Tree exceeds MAX_TREE_DEPTH of {}", ZERO_HASHES_MAX_INDEX)
+    }
+}
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum TreeHashType {
+    Basic,
+    Vector,
+    List,
+    Container,
+}
+
+pub trait TreeHash {
+    fn tree_hash_type() -> TreeHashType;
+
+    fn tree_hash_packed_encoding(&self) -> Vec<u8>;
+
+    fn tree_hash_packing_factor() -> usize;
+
+    fn tree_hash_root(&self) -> Hash256;
+}
+
+#[macro_export]
+macro_rules! tree_hash_ssz_encoding_as_vector {
+    ($type: ident) => {
+        impl tree_hash::TreeHash for $type {
+            fn tree_hash_type() -> tree_hash::TreeHashType {
+                tree_hash::TreeHashType::Vector
+            }
+
+            fn tree_hash_packed_encoding(&self) -> Vec<u8> {
+                unreachable!("Vector should never be packed.")
+            }
+
+            fn tree_hash_packing_factor() -> usize {
+                unreachable!("Vector should never be packed.")
+            }
+
+            fn tree_hash_root(&self) -> Vec<u8> {
+                tree_hash::merkle_root(&ssz::ssz_encode(self))
+            }
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! tree_hash_ssz_encoding_as_list {
+    ($type: ident) => {
+        impl tree_hash::TreeHash for $type {
+            fn tree_hash_type() -> tree_hash::TreeHashType {
+                tree_hash::TreeHashType::List
+            }
+
+            fn tree_hash_packed_encoding(&self) -> Vec<u8> {
+                unreachable!("List should never be packed.")
+            }
+
+            fn tree_hash_packing_factor() -> usize {
+                unreachable!("List should never be packed.")
+            }
+
+            fn tree_hash_root(&self) -> Vec<u8> {
+                ssz::ssz_encode(self).tree_hash_root()
+            }
+        }
+    };
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn mix_length() {
+        let hash = {
+            let mut preimage = vec![42; BYTES_PER_CHUNK];
+            preimage.append(&mut vec![42]);
+            preimage.append(&mut vec![0; BYTES_PER_CHUNK - 1]);
+            eth2_hashing::hash(&preimage)
+        };
+
+        assert_eq!(
+            mix_in_length(&Hash256::from_slice(&[42; BYTES_PER_CHUNK]), 42).as_bytes(),
+            &hash[..]
+        );
+    }
+}