Add 'plain_hasher/' from commit '10d8df665b00bc28f18f8e58aa8e0a3702318fb6'

git-subtree-dir: plain_hasher
git-subtree-mainline: d186724e50
git-subtree-split: 10d8df665b

plain_hasher/Cargo.toml

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+[package]
+name = "plain_hasher"
+description = "Hasher for 32-bit keys."
+version = "0.2.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+license = "MIT"
+keywords = ["hash", "hasher"]
+homepage = "https://github.com/paritytech/plain_hasher"
+
+[dependencies]
+crunchy = "0.1.6"
+ethereum-types = "0.3"
+hashdb = { version = "0.2.0", path = "../hashdb" }

plain_hasher/benches/bench.rs

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+// Copyright 2015-2018 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+#![feature(test)]
+
+extern crate test;
+extern crate plain_hasher;
+
+use std::hash::Hasher;
+use std::collections::hash_map::DefaultHasher;
+use test::{Bencher, black_box};
+use plain_hasher::PlainHasher;
+
+#[bench]
+fn write_plain_hasher(b: &mut Bencher) {
+	b.iter(|| {
+		let n: u8 = black_box(100);
+		(0..n).fold(PlainHasher::default(), |mut old, new| {
+			let bb = black_box([new; 32]);
+			old.write(&bb as &[u8]);
+			old
+		});
+	});
+}
+
+#[bench]
+fn write_default_hasher(b: &mut Bencher) {
+	b.iter(|| {
+		let n: u8 = black_box(100);
+		(0..n).fold(DefaultHasher::default(), |mut old, new| {
+			let bb = black_box([new; 32]);
+			old.write(&bb as &[u8]);
+			old
+		});
+	});
+}

plain_hasher/src/lib.rs

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+// Copyright 2015-2018 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+#[macro_use]
+extern crate crunchy;
+extern crate ethereum_types;
+extern crate hashdb;
+
+use ethereum_types::H256;
+// use hashdb::Hasher;
+use std::hash;
+use std::collections::{HashMap, HashSet};
+/// Specialized version of `HashMap` with H256 keys and fast hashing function.
+pub type H256FastMap<T> = HashMap<H256, T, hash::BuildHasherDefault<PlainHasher>>;
+/// Specialized version of `HashSet` with H256 keys and fast hashing function.
+pub type H256FastSet = HashSet<H256, hash::BuildHasherDefault<PlainHasher>>;
+
+/// Hasher that just takes 8 bytes of the provided value.
+/// May only be used for keys which are 32 bytes.
+#[derive(Default)]
+pub struct PlainHasher {
+	prefix: u64,
+}
+
+impl hash::Hasher for PlainHasher {
+	#[inline]
+	fn finish(&self) -> u64 {
+		self.prefix
+	}
+
+	#[inline]
+	#[allow(unused_assignments)]
+	fn write(&mut self, bytes: &[u8]) {
+		debug_assert!(bytes.len() == 32);
+		let mut bytes_ptr = bytes.as_ptr();
+		let mut prefix_ptr = &mut self.prefix as *mut u64 as *mut u8;
+
+		unroll! {
+			for _i in 0..8 {
+				unsafe { 
+					*prefix_ptr ^= (*bytes_ptr ^ *bytes_ptr.offset(8)) ^ (*bytes_ptr.offset(16) ^ *bytes_ptr.offset(24));
+					bytes_ptr = bytes_ptr.offset(1);
+					prefix_ptr = prefix_ptr.offset(1);
+				}
+			}
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use std::hash::Hasher;
+	use super::PlainHasher;
+
+	#[test]
+	fn it_works() {
+		let mut bytes = [32u8; 32];
+		bytes[0] = 15;
+		let mut hasher = PlainHasher::default();
+		hasher.write(&bytes);
+		assert_eq!(hasher.prefix, 47);
+	}
+}