Auto merge of #37312 - arthurprs:sip-smaller, r=alexcrichton

Small improvement to SipHasher Very small but constant improvement, the objective is to lower latency for u16, u32 and small strings. CC #35735 ``` ➜ siphash-bench git:(master) ✗ sudo nice -n -20 target/release/foo-648738a54f390643 --bench | tee benches.txt [sudo] password for arthurprs: running 62 tests test _same ... bench: 0 ns/iter (+/- 0) test _warmup ... bench: 0 ns/iter (+/- 0) test rust_siphash13::int_u16 ... bench: 12 ns/iter (+/- 1) test rust_siphash13::int_u32 ... bench: 14 ns/iter (+/- 0) test rust_siphash13::int_u64 ... bench: 11 ns/iter (+/- 1) test rust_siphash13::int_u8 ... bench: 11 ns/iter (+/- 1) test rust_siphash13::slice::_10 ... bench: 18 ns/iter (+/- 1) test rust_siphash13::slice::_100 ... bench: 42 ns/iter (+/- 2) test rust_siphash13::slice::_11 ... bench: 19 ns/iter (+/- 1) test rust_siphash13::slice::_12 ... bench: 21 ns/iter (+/- 3) test rust_siphash13::slice::_2 ... bench: 16 ns/iter (+/- 2) test rust_siphash13::slice::_200 ... bench: 68 ns/iter (+/- 3) test rust_siphash13::slice::_3 ... bench: 17 ns/iter (+/- 3) test rust_siphash13::slice::_4 ... bench: 18 ns/iter (+/- 1) test rust_siphash13::slice::_5 ... bench: 19 ns/iter (+/- 4) test rust_siphash13::slice::_6 ... bench: 19 ns/iter (+/- 1) test rust_siphash13::slice::_7 ... bench: 20 ns/iter (+/- 1) test rust_siphash13::slice::_8 ... bench: 16 ns/iter (+/- 1) test rust_siphash13::slice::_9 ... bench: 18 ns/iter (+/- 2) test rust_siphash13::str_::_10 ... bench: 18 ns/iter (+/- 1) test rust_siphash13::str_::_100 ... bench: 41 ns/iter (+/- 2) test rust_siphash13::str_::_11 ... bench: 19 ns/iter (+/- 1) test rust_siphash13::str_::_12 ... bench: 20 ns/iter (+/- 2) test rust_siphash13::str_::_2 ... bench: 16 ns/iter (+/- 1) test rust_siphash13::str_::_200 ... bench: 68 ns/iter (+/- 3) test rust_siphash13::str_::_3 ... bench: 17 ns/iter (+/- 1) test rust_siphash13::str_::_4 ... bench: 18 ns/iter (+/- 2) test rust_siphash13::str_::_5 ... bench: 19 ns/iter (+/- 6) test rust_siphash13::str_::_6 ... bench: 20 ns/iter (+/- 5) test rust_siphash13::str_::_7 ... bench: 23 ns/iter (+/- 1) test rust_siphash13::str_::_8 ... bench: 15 ns/iter (+/- 1) test rust_siphash13::str_::_9 ... bench: 17 ns/iter (+/- 1) test sip1b::int_u16 ... bench: 10 ns/iter (+/- 1) test sip1b::int_u32 ... bench: 9 ns/iter (+/- 1) test sip1b::int_u64 ... bench: 12 ns/iter (+/- 1) test sip1b::int_u8 ... bench: 7 ns/iter (+/- 0) test sip1b::slice::_10 ... bench: 12 ns/iter (+/- 1) test sip1b::slice::_100 ... bench: 33 ns/iter (+/- 2) test sip1b::slice::_11 ... bench: 13 ns/iter (+/- 0) test sip1b::slice::_12 ... bench: 12 ns/iter (+/- 1) test sip1b::slice::_2 ... bench: 10 ns/iter (+/- 0) test sip1b::slice::_200 ... bench: 62 ns/iter (+/- 2) test sip1b::slice::_3 ... bench: 10 ns/iter (+/- 1) test sip1b::slice::_4 ... bench: 9 ns/iter (+/- 0) test sip1b::slice::_5 ... bench: 10 ns/iter (+/- 1) test sip1b::slice::_6 ... bench: 10 ns/iter (+/- 0) test sip1b::slice::_7 ... bench: 11 ns/iter (+/- 0) test sip1b::slice::_8 ... bench: 11 ns/iter (+/- 1) test sip1b::slice::_9 ... bench: 12 ns/iter (+/- 1) test sip1b::str_::_10 ... bench: 15 ns/iter (+/- 1) test sip1b::str_::_100 ... bench: 37 ns/iter (+/- 3) test sip1b::str_::_11 ... bench: 16 ns/iter (+/- 1) test sip1b::str_::_12 ... bench: 14 ns/iter (+/- 1) test sip1b::str_::_2 ... bench: 13 ns/iter (+/- 1) test sip1b::str_::_200 ... bench: 67 ns/iter (+/- 5) test sip1b::str_::_3 ... bench: 14 ns/iter (+/- 2) test sip1b::str_::_4 ... bench: 12 ns/iter (+/- 1) test sip1b::str_::_5 ... bench: 13 ns/iter (+/- 1) test sip1b::str_::_6 ... bench: 13 ns/iter (+/- 0) test sip1b::str_::_7 ... bench: 16 ns/iter (+/- 1) test sip1b::str_::_8 ... bench: 14 ns/iter (+/- 1) test sip1b::str_::_9 ... bench: 15 ns/iter (+/- 1) test result: ok. 0 passed; 0 failed; 0 ignored; 62 measured ➜ siphash-bench git:(master) ✗ cargo benchcmp rust_siphash13:: sip1b:: benches.txt name rust_siphash13:: ns/iter sip1b:: ns/iter diff ns/iter diff % int_u16 12 10 -2 -16.67% int_u32 14 9 -5 -35.71% int_u64 11 12 1 9.09% int_u8 11 7 -4 -36.36% slice::_10 18 12 -6 -33.33% slice::_100 42 33 -9 -21.43% slice::_11 19 13 -6 -31.58% slice::_12 21 12 -9 -42.86% slice::_2 16 10 -6 -37.50% slice::_200 68 62 -6 -8.82% slice::_3 17 10 -7 -41.18% slice::_4 18 9 -9 -50.00% slice::_5 19 10 -9 -47.37% slice::_6 19 10 -9 -47.37% slice::_7 20 11 -9 -45.00% slice::_8 16 11 -5 -31.25% slice::_9 18 12 -6 -33.33% str_::_10 18 15 -3 -16.67% str_::_100 41 37 -4 -9.76% str_::_11 19 16 -3 -15.79% str_::_12 20 14 -6 -30.00% str_::_2 16 13 -3 -18.75% str_::_200 68 67 -1 -1.47% str_::_3 17 14 -3 -17.65% str_::_4 18 12 -6 -33.33% str_::_5 19 13 -6 -31.58% str_::_6 20 13 -7 -35.00% str_::_7 23 16 -7 -30.43% str_::_8 15 14 -1 -6.67% str_::_9 17 15 -2 -11.76% ``` from a modified hash-rs suite (preallocating maps and adding having slice/str variants) graph version: http://imgur.com/a/DuoI4 ``` ➜ hash-rs git:(rfc-extend-hasher) ✗ cargo benchcmp sip13:: sip13opt:: benches.txt name sip13:: ns/iter sip13opt:: ns/iter diff ns/iter diff % slice::mapcountdense_000000001 27,343 (36 MB/s) 26,401 (37 MB/s) -942 -3.45% slice::mapcountdense_000000002 28,982 (69 MB/s) 26,807 (74 MB/s) -2,175 -7.50% slice::mapcountdense_000000003 29,304 (102 MB/s) 27,360 (109 MB/s) -1,944 -6.63% slice::mapcountdense_000000004 30,411 (131 MB/s) 25,888 (154 MB/s) -4,523 -14.87% slice::mapcountdense_000000005 32,625 (153 MB/s) 27,486 (181 MB/s) -5,139 -15.75% slice::mapcountdense_000000006 34,920 (171 MB/s) 27,204 (220 MB/s) -7,716 -22.10% slice::mapcountdense_000000007 33,497 (208 MB/s) 28,330 (247 MB/s) -5,167 -15.43% slice::mapcountdense_000000008 31,153 (256 MB/s) 28,617 (279 MB/s) -2,536 -8.14% slice::mapcountdense_000000009 30,745 (292 MB/s) 29,666 (303 MB/s) -1,079 -3.51% slice::mapcountdense_000000010 31,509 (317 MB/s) 29,804 (335 MB/s) -1,705 -5.41% slice::mapcountdense_000000011 32,526 (338 MB/s) 30,520 (360 MB/s) -2,006 -6.17% slice::mapcountdense_000000012 32,981 (363 MB/s) 28,739 (417 MB/s) -4,242 -12.86% slice::mapcountdense_000000013 34,713 (374 MB/s) 30,348 (428 MB/s) -4,365 -12.57% slice::mapcountdense_000000014 34,635 (404 MB/s) 29,974 (467 MB/s) -4,661 -13.46% slice::mapcountdense_000000015 35,924 (417 MB/s) 30,584 (490 MB/s) -5,340 -14.86% slice::mapcountdense_000000016 31,939 (500 MB/s) 30,564 (523 MB/s) -1,375 -4.31% slice::mapcountdense_000000032 36,545 (875 MB/s) 34,833 (918 MB/s) -1,712 -4.68% slice::mapcountdense_000000064 44,691 (1432 MB/s) 43,912 (1457 MB/s) -779 -1.74% slice::mapcountdense_000000128 67,210 (1904 MB/s) 64,630 (1980 MB/s) -2,580 -3.84% slice::mapcountdense_000000256 110,320 (2320 MB/s) 108,713 (2354 MB/s) -1,607 -1.46% slice::mapcountsparse_000000001 29,686 (33 MB/s) 28,673 (34 MB/s) -1,013 -3.41% slice::mapcountsparse_000000002 32,073 (62 MB/s) 30,519 (65 MB/s) -1,554 -4.85% slice::mapcountsparse_000000003 33,184 (90 MB/s) 31,208 (96 MB/s) -1,976 -5.95% slice::mapcountsparse_000000004 34,344 (116 MB/s) 30,242 (132 MB/s) -4,102 -11.94% slice::mapcountsparse_000000005 34,536 (144 MB/s) 30,552 (163 MB/s) -3,984 -11.54% slice::mapcountsparse_000000006 35,791 (167 MB/s) 30,813 (194 MB/s) -4,978 -13.91% slice::mapcountsparse_000000007 36,773 (190 MB/s) 31,362 (223 MB/s) -5,411 -14.71% slice::mapcountsparse_000000008 33,101 (241 MB/s) 32,399 (246 MB/s) -702 -2.12% slice::mapcountsparse_000000009 34,025 (264 MB/s) 33,065 (272 MB/s) -960 -2.82% slice::mapcountsparse_000000010 34,755 (287 MB/s) 33,152 (301 MB/s) -1,603 -4.61% slice::mapcountsparse_000000011 35,682 (308 MB/s) 33,631 (327 MB/s) -2,051 -5.75% slice::mapcountsparse_000000012 36,422 (329 MB/s) 32,604 (368 MB/s) -3,818 -10.48% slice::mapcountsparse_000000013 37,561 (346 MB/s) 32,978 (394 MB/s) -4,583 -12.20% slice::mapcountsparse_000000014 38,476 (363 MB/s) 33,376 (419 MB/s) -5,100 -13.26% slice::mapcountsparse_000000015 39,202 (382 MB/s) 33,750 (444 MB/s) -5,452 -13.91% slice::mapcountsparse_000000016 34,898 (458 MB/s) 33,621 (475 MB/s) -1,277 -3.66% slice::mapcountsparse_000000032 39,767 (804 MB/s) 38,013 (841 MB/s) -1,754 -4.41% slice::mapcountsparse_000000064 47,810 (1338 MB/s) 46,332 (1381 MB/s) -1,478 -3.09% slice::mapcountsparse_000000128 64,519 (1983 MB/s) 63,322 (2021 MB/s) -1,197 -1.86% slice::mapcountsparse_000000256 101,042 (2533 MB/s) 99,754 (2566 MB/s) -1,288 -1.27% str_::mapcountdense_000000001 27,183 (36 MB/s) 24,007 (41 MB/s) -3,176 -11.68% str_::mapcountdense_000000002 28,940 (69 MB/s) 24,574 (81 MB/s) -4,366 -15.09% str_::mapcountdense_000000003 29,000 (103 MB/s) 24,687 (121 MB/s) -4,313 -14.87% str_::mapcountdense_000000004 29,822 (134 MB/s) 24,377 (164 MB/s) -5,445 -18.26% str_::mapcountdense_000000005 31,962 (156 MB/s) 25,184 (198 MB/s) -6,778 -21.21% str_::mapcountdense_000000006 32,218 (186 MB/s) 25,020 (239 MB/s) -7,198 -22.34% str_::mapcountdense_000000007 35,482 (197 MB/s) 27,705 (252 MB/s) -7,777 -21.92% str_::mapcountdense_000000008 28,643 (279 MB/s) 25,563 (312 MB/s) -3,080 -10.75% str_::mapcountdense_000000009 30,112 (298 MB/s) 26,773 (336 MB/s) -3,339 -11.09% str_::mapcountdense_000000010 31,554 (316 MB/s) 27,607 (362 MB/s) -3,947 -12.51% str_::mapcountdense_000000011 32,062 (343 MB/s) 27,770 (396 MB/s) -4,292 -13.39% str_::mapcountdense_000000012 32,258 (372 MB/s) 25,612 (468 MB/s) -6,646 -20.60% str_::mapcountdense_000000013 33,544 (387 MB/s) 26,908 (483 MB/s) -6,636 -19.78% str_::mapcountdense_000000014 34,681 (403 MB/s) 27,267 (513 MB/s) -7,414 -21.38% str_::mapcountdense_000000015 37,883 (395 MB/s) 30,226 (496 MB/s) -7,657 -20.21% str_::mapcountdense_000000016 30,299 (528 MB/s) 27,960 (572 MB/s) -2,339 -7.72% str_::mapcountdense_000000032 34,372 (930 MB/s) 32,736 (977 MB/s) -1,636 -4.76% str_::mapcountdense_000000048 38,610 (1243 MB/s) 36,437 (1317 MB/s) -2,173 -5.63% str_::mapcountdense_000000064 43,052 (1486 MB/s) 41,269 (1550 MB/s) -1,783 -4.14% str_::mapcountdense_000000128 64,059 (1998 MB/s) 62,007 (2064 MB/s) -2,052 -3.20% str_::mapcountdense_000000256 109,608 (2335 MB/s) 107,184 (2388 MB/s) -2,424 -2.21% str_::mapcountsparse_000000001 29,155 (34 MB/s) 26,151 (38 MB/s) -3,004 -10.30% str_::mapcountsparse_000000002 31,536 (63 MB/s) 27,787 (71 MB/s) -3,749 -11.89% str_::mapcountsparse_000000003 32,524 (92 MB/s) 27,861 (107 MB/s) -4,663 -14.34% str_::mapcountsparse_000000004 33,535 (119 MB/s) 27,585 (145 MB/s) -5,950 -17.74% str_::mapcountsparse_000000005 34,239 (146 MB/s) 27,520 (181 MB/s) -6,719 -19.62% str_::mapcountsparse_000000006 35,485 (169 MB/s) 27,437 (218 MB/s) -8,048 -22.68% str_::mapcountsparse_000000007 39,098 (179 MB/s) 30,465 (229 MB/s) -8,633 -22.08% str_::mapcountsparse_000000008 30,882 (259 MB/s) 29,215 (273 MB/s) -1,667 -5.40% str_::mapcountsparse_000000009 33,375 (269 MB/s) 29,301 (307 MB/s) -4,074 -12.21% str_::mapcountsparse_000000010 33,531 (298 MB/s) 29,008 (344 MB/s) -4,523 -13.49% str_::mapcountsparse_000000011 34,607 (317 MB/s) 29,800 (369 MB/s) -4,807 -13.89% str_::mapcountsparse_000000012 35,700 (336 MB/s) 28,380 (422 MB/s) -7,320 -20.50% str_::mapcountsparse_000000013 36,692 (354 MB/s) 29,350 (442 MB/s) -7,342 -20.01% str_::mapcountsparse_000000014 37,326 (375 MB/s) 29,285 (478 MB/s) -8,041 -21.54% str_::mapcountsparse_000000015 41,098 (364 MB/s) 33,073 (453 MB/s) -8,025 -19.53% str_::mapcountsparse_000000016 33,046 (484 MB/s) 30,717 (520 MB/s) -2,329 -7.05% str_::mapcountsparse_000000032 37,471 (853 MB/s) 35,542 (900 MB/s) -1,929 -5.15% str_::mapcountsparse_000000048 41,324 (1161 MB/s) 39,332 (1220 MB/s) -1,992 -4.82% str_::mapcountsparse_000000064 45,858 (1395 MB/s) 43,802 (1461 MB/s) -2,056 -4.48% str_::mapcountsparse_000000128 62,471 (2048 MB/s) 60,683 (2109 MB/s) -1,788 -2.86% str_::mapcountsparse_000000256 101,283 (2527 MB/s) 97,655 (2621 MB/s) -3,628 -3.58% ```
rust-lang · Oct 26, 2016 · a5b6a9f · a5b6a9f
2 parents a6b3b01 + a319d13
commit a5b6a9f
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Showing 2 changed files with 118 additions and 50 deletions.
diff --git a/src/libcore/hash/sip.rs b/src/libcore/hash/sip.rs
@@ -14,6 +14,8 @@
 
 use marker::PhantomData;
 use ptr;
+use cmp;
+use mem;
 
 /// An implementation of SipHash 1-3.
 ///
@@ -78,45 +80,6 @@ struct State {
     v3: u64,
 }
 
-// sadly, these macro definitions can't appear later,
-// because they're needed in the following defs;
-// this design could be improved.
-
-macro_rules! u8to64_le {
-    ($buf:expr, $i:expr) =>
-    ($buf[0+$i] as u64 |
-     ($buf[1+$i] as u64) << 8 |
-     ($buf[2+$i] as u64) << 16 |
-     ($buf[3+$i] as u64) << 24 |
-     ($buf[4+$i] as u64) << 32 |
-     ($buf[5+$i] as u64) << 40 |
-     ($buf[6+$i] as u64) << 48 |
-     ($buf[7+$i] as u64) << 56);
-    ($buf:expr, $i:expr, $len:expr) =>
-    ({
-        let mut t = 0;
-        let mut out = 0;
-        while t < $len {
-            out |= ($buf[t+$i] as u64) << t*8;
-            t += 1;
-        }
-        out
-    });
-}
-
-/// Load a full u64 word from a byte stream, in LE order. Use
-/// `copy_nonoverlapping` to let the compiler generate the most efficient way
-/// to load u64 from a possibly unaligned address.
-///
-/// Unsafe because: unchecked indexing at i..i+8
-#[inline]
-unsafe fn load_u64_le(buf: &[u8], i: usize) -> u64 {
-    debug_assert!(i + 8 <= buf.len());
-    let mut data = 0u64;
-    ptr::copy_nonoverlapping(buf.get_unchecked(i), &mut data as *mut _ as *mut u8, 8);
-    data.to_le()
-}
-
 macro_rules! compress {
     ($state:expr) => ({
         compress!($state.v0, $state.v1, $state.v2, $state.v3)
@@ -132,6 +95,47 @@ macro_rules! compress {
     });
 }
 
+/// Load an integer of the desired type from a byte stream, in LE order. Uses
+/// `copy_nonoverlapping` to let the compiler generate the most efficient way
+/// to load it from a possibly unaligned address.
+///
+/// Unsafe because: unchecked indexing at i..i+size_of(int_ty)
+macro_rules! load_int_le {
+    ($buf:expr, $i:expr, $int_ty:ident) =>
+    ({
+       debug_assert!($i + mem::size_of::<$int_ty>() <= $buf.len());
+       let mut data = 0 as $int_ty;
+       ptr::copy_nonoverlapping($buf.get_unchecked($i),
+                                &mut data as *mut _ as *mut u8,
+                                mem::size_of::<$int_ty>());
+       data.to_le()
+    });
+}
+
+/// Load an u64 using up to 7 bytes of a byte slice.
+///
+/// Unsafe because: unchecked indexing at start..start+len
+#[inline]
+unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
+    debug_assert!(len < 8);
+    let mut i = 0; // current byte index (from LSB) in the output u64
+    let mut out = 0;
+    if i + 3 < len {
+        out = load_int_le!(buf, start + i, u32) as u64;
+        i += 4;
+    }
+    if i + 1 < len {
+        out |= (load_int_le!(buf, start + i, u16) as u64) << (i * 8);
+        i += 2
+    }
+    if i < len {
+        out |= (*buf.get_unchecked(start + i) as u64) << (i * 8);
+        i += 1;
+    }
+    debug_assert_eq!(i, len);
+    out
+}
+
 impl SipHasher {
     /// Creates a new `SipHasher` with the two initial keys set to 0.
     #[inline]
@@ -220,6 +224,37 @@ impl<S: Sip> Hasher<S> {
         self.state.v3 = self.k1 ^ 0x7465646279746573;
         self.ntail = 0;
     }
+
+    // Specialized write function that is only valid for buffers with len <= 8.
+    // It's used to force inlining of write_u8 and write_usize, those would normally be inlined
+    // except for composite types (that includes slices and str hashing because of delimiter).
+    // Without this extra push the compiler is very reluctant to inline delimiter writes,
+    // degrading performance substantially for the most common use cases.
+    #[inline(always)]
+    fn short_write(&mut self, msg: &[u8]) {
+        debug_assert!(msg.len() <= 8);
+        let length = msg.len();
+        self.length += length;
+
+        let needed = 8 - self.ntail;
+        let fill = cmp::min(length, needed);
+        if fill == 8 {
+            self.tail = unsafe { load_int_le!(msg, 0, u64) };
+        } else {
+            self.tail |= unsafe { u8to64_le(msg, 0, fill) } << (8 * self.ntail);
+            if length < needed {
+                self.ntail += length;
+                return;
+            }
+        }
+        self.state.v3 ^= self.tail;
+        S::c_rounds(&mut self.state);
+        self.state.v0 ^= self.tail;
+
+        // Buffered tail is now flushed, process new input.
+        self.ntail = length - needed;
+        self.tail = unsafe { u8to64_le(msg, needed, self.ntail) };
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -262,6 +297,21 @@ impl super::Hasher for SipHasher24 {
 }
 
 impl<S: Sip> super::Hasher for Hasher<S> {
+    // see short_write comment for explanation
+    #[inline]
+    fn write_usize(&mut self, i: usize) {
+        let bytes = unsafe {
+            ::slice::from_raw_parts(&i as *const usize as *const u8, mem::size_of::<usize>())
+        };
+        self.short_write(bytes);
+    }
+
+    // see short_write comment for explanation
+    #[inline]
+    fn write_u8(&mut self, i: u8) {
+        self.short_write(&[i]);
+    }
+
     #[inline]
     fn write(&mut self, msg: &[u8]) {
         let length = msg.len();
@@ -271,19 +321,16 @@ impl<S: Sip> super::Hasher for Hasher<S> {
 
         if self.ntail != 0 {
             needed = 8 - self.ntail;
+            self.tail |= unsafe { u8to64_le(msg, 0, cmp::min(length, needed)) } << 8 * self.ntail;
             if length < needed {
-                self.tail |= u8to64_le!(msg, 0, length) << 8 * self.ntail;
                 self.ntail += length;
                 return
+            } else {
+                self.state.v3 ^= self.tail;
+                S::c_rounds(&mut self.state);
+                self.state.v0 ^= self.tail;
+                self.ntail = 0;
             }
-
-            let m = self.tail | u8to64_le!(msg, 0, needed) << 8 * self.ntail;
-
-            self.state.v3 ^= m;
-            S::c_rounds(&mut self.state);
-            self.state.v0 ^= m;
-
-            self.ntail = 0;
         }
 
         // Buffered tail is now flushed, process new input.
@@ -292,7 +339,7 @@ impl<S: Sip> super::Hasher for Hasher<S> {
 
         let mut i = needed;
         while i < len - left {
-            let mi = unsafe { load_u64_le(msg, i) };
+            let mi = unsafe { load_int_le!(msg, i, u64) };
 
             self.state.v3 ^= mi;
             S::c_rounds(&mut self.state);
@@ -301,7 +348,7 @@ impl<S: Sip> super::Hasher for Hasher<S> {
             i += 8;
         }
 
-        self.tail = u8to64_le!(msg, i, left);
+        self.tail = unsafe { u8to64_le(msg, i, left) };
         self.ntail = left;
     }
 

diff --git a/src/libcoretest/hash/sip.rs b/src/libcoretest/hash/sip.rs
@@ -14,6 +14,7 @@ use test::{Bencher, black_box};
 
 use core::hash::{Hash, Hasher};
 use core::hash::{SipHasher, SipHasher13, SipHasher24};
+use core::{slice, mem};
 
 // Hash just the bytes of the slice, without length prefix
 struct Bytes<'a>(&'a [u8]);
@@ -327,6 +328,26 @@ fn test_hash_no_concat_alias() {
     assert!(hash(&v) != hash(&w));
 }
 
+#[test]
+fn test_write_short_works() {
+    let test_usize = 0xd0c0b0a0usize;
+    let mut h1 = SipHasher24::new();
+    h1.write_usize(test_usize);
+    h1.write(b"bytes");
+    h1.write(b"string");
+    h1.write_u8(0xFFu8);
+    h1.write_u8(0x01u8);
+    let mut h2 = SipHasher24::new();
+    h2.write(unsafe {
+        slice::from_raw_parts(&test_usize as *const _ as *const u8,
+                              mem::size_of::<usize>())
+    });
+    h2.write(b"bytes");
+    h2.write(b"string");
+    h2.write(&[0xFFu8, 0x01u8]);
+    assert_eq!(h1.finish(), h2.finish());
+}
+
 #[bench]
 fn bench_str_under_8_bytes(b: &mut Bencher) {
     let s = "foo";