Forward port blake2 storage support (#2360)

* move storage maps to blake2_128 (#2268)

* remove default hash, introduce twox_128 and blake2

* use blake2_128 & create ext_blake2_128

* refactor code

* add benchmark

* factorize generator

* fix

* parameterizable hasher

* some fix

* fix

* fix

* fix

* metadata

* fix

* remove debug print

* map -> blake2_256

* fix test

* fix test

* Apply suggestions from code review

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

* impl twox 128 concat (#2353)

* impl twox_128_concat

* comment addressed

* fix

* impl twox_128->64_concat

* fix test

* Fix compilation and cleanup some docs

* Apply suggestions from code review

Co-Authored-By: bkchr <bkchr@users.noreply.github.com>

substrate/core/primitives/benches/benches.rs

@@ -0,0 +1,60 @@
+// Copyright 2019 Parity Technologies
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// TODO: Move benchmark to criterion #2354
+#![feature(test)]
+
+extern crate test;
+use hex_literal::{hex, hex_impl};
+use substrate_primitives::hashing::{twox_128, blake2_128};
+
+
+const MAX_KEY_SIZE: u32 = 32;
+
+fn data_set() -> Vec<Vec<u8>> {
+	use rand::SeedableRng;
+	use rand::Rng;
+
+	let rnd: [u8; 32] = rand::rngs::StdRng::seed_from_u64(12).gen();
+	let mut rnd = rnd.iter().cycle();
+	let mut res = Vec::new();
+	for size in 1..=MAX_KEY_SIZE {
+		for _ in 0..1_000 {
+			let value = (0..size)
+				.map(|_| rnd.next().unwrap().clone())
+				.collect();
+			res.push(value);
+		}
+	}
+	res
+}
+
+fn bench_hash_128(b: &mut test::Bencher, f: &Fn(&[u8]) -> [u8; 16]) {
+	let data_set = data_set();
+	b.iter(|| {
+		for data in &data_set {
+			let _a = f(data);
+		}
+	});
+}
+
+#[bench]
+fn bench_blake2_128(b: &mut test::Bencher) {
+	bench_hash_128(b, &blake2_128);
+}
+
+#[bench]
+fn bench_twox_128(b: &mut test::Bencher) {
+	bench_hash_128(b, &twox_128);
+}