optimize double map first key hash (#2451)

* fix double map encoding it is now encoded as specified in the doc

substrate/srml/support/test/tests/final_keys.rs

@@ -0,0 +1,81 @@
+use runtime_io::{with_externalities, Blake2Hasher};
+use srml_support::{StorageValue, StorageMap, StorageDoubleMap};
+use srml_support::storage::unhashed;
+use srml_support::runtime_primitives::BuildStorage;
+use parity_codec::Encode;
+
+pub trait Trait {
+	type Origin;
+	type BlockNumber;
+}
+
+srml_support::decl_module! {
+	pub struct Module<T: Trait> for enum Call where origin: T::Origin {}
+}
+
+srml_support::decl_storage!{
+	trait Store for Module<T: Trait> as Module {
+		pub Value config(value): u32;
+
+		pub Map: map u32 => u32;
+		pub Map2: map hasher(twox_128) u32 => u32;
+
+		pub LinkedMap: linked_map u32 => u32;
+		pub LinkedMap2: linked_map hasher(twox_128) u32 => u32;
+
+		pub DoubleMap: double_map u32, blake2_256(u32) => u32;
+		pub DoubleMap2: double_map hasher(twox_128) u32, blake2_128(u32) => u32;
+	}
+}
+
+struct Test;
+impl Trait for Test {
+	type BlockNumber = u32;
+	type Origin = u32;
+}
+
+fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher> {
+	GenesisConfig::<Test>::default().build_storage().unwrap().0.into()
+}
+
+#[test]
+fn final_keys() {
+	with_externalities(&mut new_test_ext(), || {
+		<Value<Test>>::put(1);
+		assert_eq!(unhashed::get::<u32>(&runtime_io::twox_128(b"Module Value")), Some(1u32));
+
+		<Map<Test>>::insert(1, 2);
+		let mut k = b"Module Map".to_vec();
+		k.extend(1u32.encode());
+		assert_eq!(unhashed::get::<u32>(&runtime_io::blake2_256(&k)), Some(2u32));
+
+		<Map2<Test>>::insert(1, 2);
+		let mut k = b"Module Map2".to_vec();
+		k.extend(1u32.encode());
+		assert_eq!(unhashed::get::<u32>(&runtime_io::twox_128(&k)), Some(2u32));
+
+		<LinkedMap<Test>>::insert(1, 2);
+		let mut k = b"Module LinkedMap".to_vec();
+		k.extend(1u32.encode());
+		assert_eq!(unhashed::get::<u32>(&runtime_io::blake2_256(&k)), Some(2u32));
+
+		<LinkedMap2<Test>>::insert(1, 2);
+		let mut k = b"Module LinkedMap2".to_vec();
+		k.extend(1u32.encode());
+		assert_eq!(unhashed::get::<u32>(&runtime_io::twox_128(&k)), Some(2u32));
+
+		<DoubleMap<Test>>::insert(1, 2, 3);
+		let mut k = b"Module DoubleMap".to_vec();
+		k.extend(1u32.encode());
+		let mut k = runtime_io::blake2_256(&k).to_vec();
+		k.extend(&runtime_io::blake2_256(&2u32.encode()));
+		assert_eq!(unhashed::get::<u32>(&k), Some(3u32));
+
+		<DoubleMap2<Test>>::insert(1, 2, 3);
+		let mut k = b"Module DoubleMap2".to_vec();
+		k.extend(1u32.encode());
+		let mut k = runtime_io::twox_128(&k).to_vec();
+		k.extend(&runtime_io::blake2_128(&2u32.encode()));
+		assert_eq!(unhashed::get::<u32>(&k), Some(3u32));
+	});
+}