Hash up to 8 bytes at once with FxHasher

Author: Zoxc

Cargo.lock

@@ -9,3 +9,4 @@ keywords = ["hash", "fxhash", "rustc"]
 repository = "https://github.com/rust-lang-nursery/rustc-hash"
 
 [dependencies]
+byteorder = "1.1"

Cargo.toml

@@ -18,10 +18,15 @@
 //! map.insert(22, 44);
 //! ```
 
+extern crate byteorder;
+
 use std::collections::{HashMap, HashSet};
 use std::default::Default;
 use std::hash::{Hasher, BuildHasherDefault};
 use std::ops::BitXor;
+use std::mem::size_of;
+
+use byteorder::{ByteOrder, NativeEndian};
 
 /// Type alias for a hashmap using the `fx` hash algorithm.
 pub type FxHashMap<K, V> = HashMap<K, V, BuildHasherDefault<FxHasher>>;
@@ -65,11 +70,30 @@ impl FxHasher {
 
 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);
+    fn write(&mut self, mut bytes: &[u8]) {
+        #[cfg(target_pointer_width = "32")]
+        let read_usize = |bytes| NativeEndian::read_u32(bytes);
+        #[cfg(target_pointer_width = "64")]
+        let read_usize = |bytes| NativeEndian::read_u64(bytes);
+
+        let mut hash = FxHasher { hash: self.hash };
+        assert!(size_of::<usize>() <= 8);
+        while bytes.len() >= size_of::<usize>() {
+            hash.add_to_hash(read_usize(bytes) as usize);
+            bytes = &bytes[size_of::<usize>()..];
+        }
+        if (size_of::<usize>() > 4) && (bytes.len() >= 4) {
+            hash.add_to_hash(NativeEndian::read_u32(bytes) as usize);
+            bytes = &bytes[4..];
+        }
+        if (size_of::<usize>() > 2) && bytes.len() >= 2 {
+            hash.add_to_hash(NativeEndian::read_u16(bytes) as usize);
+            bytes = &bytes[2..];
+        }
+        if (size_of::<usize>() > 1) && bytes.len() >= 1 {
+            hash.add_to_hash(bytes[0] as usize);
         }
+        self.hash = hash.hash;
     }
 
     #[inline]