Add from_hashable with SeaHash implementation

Author: dhardy

benches/hash.rs

@@ -0,0 +1,55 @@
+#![feature(test)]
+
+extern crate test;
+extern crate rand;
+extern crate rand_core;
+
+use std::mem::{size_of, size_of_val};
+use test::{black_box, Bencher};
+use rand::{Rng, thread_rng, random};
+use rand::hash::*;
+
+#[bench]
+fn hash_u64(b: &mut Bencher) {
+    const N: u64 = 100;
+    let mut x: u64 = random();
+    b.iter(|| {
+        for _ in 0..N {
+            x = x.wrapping_add(1);  // unique number each time
+            
+            // Using `hash` instead of `hash_u64` here has big performance impact — why?
+            black_box(SeaHash::new_fixed().hash_u64(x));
+            //black_box(SeaHash::new_fixed().hash(x));
+            //black_box(Hashable::hash(SeaHash::new_fixed(), x));
+        }
+    });
+    b.bytes = size_of::<u64>() as u64 * N;
+}
+
+#[bench]
+fn hash_bytes32(b: &mut Bencher) {
+    const N: u64 = 20;
+    let mut buf = [0u8; 32];
+    thread_rng().fill_bytes(&mut buf);
+    b.iter(|| {
+        for _ in 0..N {
+            buf[0] = buf[0].wrapping_add(1);  // unique number each time
+            black_box(SeaHash::hash_fixed(&buf[..]));
+        }
+    });
+    b.bytes = size_of_val(&buf) as u64 * N;
+}
+
+#[bench]
+fn hash_bytes1024(b: &mut Bencher) {
+    const N: u64 = 1;
+    let mut buf = [0u8; 1024];
+    thread_rng().fill_bytes(&mut buf);
+    b.iter(|| {
+        for _ in 0..N {
+            buf[0] = buf[0].wrapping_add(1);  // unique number each time
+            black_box(SeaHash::hash_fixed(&buf[..]));
+        }
+    });
+    b.bytes = size_of_val(&buf) as u64 * N;
+}