From 373451952e4e067648bb6fa929262c3e72be520d Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Thu, 24 May 2018 08:31:47 -0400
Subject: [PATCH] move code over from rustc

---
 .gitignore |   2 +
 Cargo.lock |   4 ++
 Cargo.toml |   6 +++
 README.md  |  14 ++++++-
 src/lib.rs | 109 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 134 insertions(+), 1 deletion(-)
 create mode 100644 .gitignore
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..53eaa21
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+**/*.rs.bk
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..0c64114
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,4 @@
+[[package]]
+name = "rustc-hash"
+version = "0.1.0"
+
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..fe105ac
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "rustc-hash"
+version = "0.1.0"
+authors = ["Niko Matsakis <niko@alum.mit.edu>"]
+
+[dependencies]
diff --git a/README.md b/README.md
index 7de120c..ce1b789 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,14 @@
 # rustc-hash
-Custom hash algorithm used by rustc (plus hashmap/set aliases): fast, deterministic, not secure
+
+A speedy hash algorithm used within rustc. The hashmap in liballoc by
+default uses SipHash which isn't quite as speedy as we want. In the
+compiler we're not really worried about DOS attempts, so we use a fast
+non-cryptographic hash.
+
+This is the same as the algorithm used by Firefox -- which is a
+homespun one not based on any widely-known algorithm -- though
+modified to produce 64-bit hash values instead of 32-bit hash
+values. It consistently out-performs an FNV-based hash within rustc
+itself -- the collision rate is similar or slightly worse than FNV,
+but the speed of the hash function itself is much higher because it
+works on up to 8 bytes at a time.
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..5bf2543
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,109 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::collections::{HashMap, HashSet};
+use std::default::Default;
+use std::hash::{Hasher, Hash, BuildHasherDefault};
+use std::ops::BitXor;
+
+pub type FxHashMap<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher>>;
+pub type FxHashSet<V> = HashSet<V, BuildHasherDefault<FxHasher>>;
+
+#[allow(non_snake_case)]
+pub fn FxHashMap<K: Hash + Eq, V>() -> FxHashMap<K, V> {
+    HashMap::default()
+}
+
+#[allow(non_snake_case)]
+pub fn FxHashSet<V: Hash + Eq>() -> FxHashSet<V> {
+    HashSet::default()
+}
+
+/// A speedy hash algorithm for use within rustc. The hashmap in liballoc
+/// by default uses SipHash which isn't quite as speedy as we want. In the
+/// compiler we're not really worried about DOS attempts, so we use a fast
+/// non-cryptographic hash.
+///
+/// This is the same as the algorithm used by Firefox -- which is a homespun
+/// one not based on any widely-known algorithm -- though modified to produce
+/// 64-bit hash values instead of 32-bit hash values. It consistently
+/// out-performs an FNV-based hash within rustc itself -- the collision rate is
+/// similar or slightly worse than FNV, but the speed of the hash function
+/// itself is much higher because it works on up to 8 bytes at a time.
+pub struct FxHasher {
+    hash: usize
+}
+
+#[cfg(target_pointer_width = "32")]
+const K: usize = 0x9e3779b9;
+#[cfg(target_pointer_width = "64")]
+const K: usize = 0x517cc1b727220a95;
+
+impl Default for FxHasher {
+    #[inline]
+    fn default() -> FxHasher {
+        FxHasher { hash: 0 }
+    }
+}
+
+impl FxHasher {
+    #[inline]
+    fn add_to_hash(&mut self, i: usize) {
+        self.hash = self.hash.rotate_left(5).bitxor(i).wrapping_mul(K);
+    }
+}
+
+impl Hasher for FxHasher {
+    #[inline]
+    fn write(&mut self, bytes: &[u8]) {
+        for byte in bytes {
+            let i = *byte;
+            self.add_to_hash(i as usize);
+        }
+    }
+
+    #[inline]
+    fn write_u8(&mut self, i: u8) {
+        self.add_to_hash(i as usize);
+    }
+
+    #[inline]
+    fn write_u16(&mut self, i: u16) {
+        self.add_to_hash(i as usize);
+    }
+
+    #[inline]
+    fn write_u32(&mut self, i: u32) {
+        self.add_to_hash(i as usize);
+    }
+
+    #[cfg(target_pointer_width = "32")]
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        self.add_to_hash(i as usize);
+        self.add_to_hash((i >> 32) as usize);
+    }
+
+    #[cfg(target_pointer_width = "64")]
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        self.add_to_hash(i as usize);
+    }
+
+    #[inline]
+    fn write_usize(&mut self, i: usize) {
+        self.add_to_hash(i);
+    }
+
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.hash as u64
+    }
+}