src/libcore/hash/sip.rs

   1 //! An implementation of SipHash.
   2
   3 // ignore-tidy-undocumented-unsafe
   4
   5 #![allow(deprecated)] // the types in this module are deprecated
   6
   7 use crate::cmp;
   8 use crate::marker::PhantomData;
   9 use crate::mem;
  10 use crate::ptr;
  11
  12 /// An implementation of SipHash 1-3.
  13 ///
  14 /// This is currently the default hashing function used by standard library
  15 /// (e.g., `collections::HashMap` uses it by default).
  16 ///
  17 /// See: <https://131002.net/siphash>
  18 #[unstable(feature = "hashmap_internals", issue = "0")]
  19 #[rustc_deprecated(
  20     since = "1.13.0",
  21     reason = "use `std::collections::hash_map::DefaultHasher` instead"
  22 )]
  23 #[derive(Debug, Clone, Default)]
  24 #[doc(hidden)]
  25 pub struct SipHasher13 {
  26     hasher: Hasher<Sip13Rounds>,
  27 }
  28
  29 /// An implementation of SipHash 2-4.
  30 ///
  31 /// See: <https://131002.net/siphash/>
  32 #[unstable(feature = "hashmap_internals", issue = "0")]
  33 #[rustc_deprecated(
  34     since = "1.13.0",
  35     reason = "use `std::collections::hash_map::DefaultHasher` instead"
  36 )]
  37 #[derive(Debug, Clone, Default)]
  38 struct SipHasher24 {
  39     hasher: Hasher<Sip24Rounds>,
  40 }
  41
  42 /// An implementation of SipHash 2-4.
  43 ///
  44 /// See: <https://131002.net/siphash/>
  45 ///
  46 /// SipHash is a general-purpose hashing function: it runs at a good
  47 /// speed (competitive with Spooky and City) and permits strong _keyed_
  48 /// hashing. This lets you key your hashtables from a strong RNG, such as
  49 /// [`rand::os::OsRng`](https://doc.rust-lang.org/rand/rand/os/struct.OsRng.html).
  50 ///
  51 /// Although the SipHash algorithm is considered to be generally strong,
  52 /// it is not intended for cryptographic purposes. As such, all
  53 /// cryptographic uses of this implementation are _strongly discouraged_.
  54 #[stable(feature = "rust1", since = "1.0.0")]
  55 #[rustc_deprecated(
  56     since = "1.13.0",
  57     reason = "use `std::collections::hash_map::DefaultHasher` instead"
  58 )]
  59 #[derive(Debug, Clone, Default)]
  60 pub struct SipHasher(SipHasher24);
  61
  62 #[derive(Debug)]
  63 struct Hasher<S: Sip> {
  64     k0: u64,
  65     k1: u64,
  66     length: usize, // how many bytes we've processed
  67     state: State,  // hash State
  68     tail: u64,     // unprocessed bytes le
  69     ntail: usize,  // how many bytes in tail are valid
  70     _marker: PhantomData<S>,
  71 }
  72
  73 #[derive(Debug, Clone, Copy)]
  74 #[repr(C)]
  75 struct State {
  76     // v0, v2 and v1, v3 show up in pairs in the algorithm,
  77     // and simd implementations of SipHash will use vectors
  78     // of v02 and v13. By placing them in this order in the struct,
  79     // the compiler can pick up on just a few simd optimizations by itself.
  80     v0: u64,
  81     v2: u64,
  82     v1: u64,
  83     v3: u64,
  84 }
  85
  86 macro_rules! compress {
  87     ($state:expr) => {{ compress!($state.v0, $state.v1, $state.v2, $state.v3) }};
  88     ($v0:expr, $v1:expr, $v2:expr, $v3:expr) => {{
  89         $v0 = $v0.wrapping_add($v1);
  90         $v1 = $v1.rotate_left(13);
  91         $v1 ^= $v0;
  92         $v0 = $v0.rotate_left(32);
  93         $v2 = $v2.wrapping_add($v3);
  94         $v3 = $v3.rotate_left(16);
  95         $v3 ^= $v2;
  96         $v0 = $v0.wrapping_add($v3);
  97         $v3 = $v3.rotate_left(21);
  98         $v3 ^= $v0;
  99         $v2 = $v2.wrapping_add($v1);
 100         $v1 = $v1.rotate_left(17);
 101         $v1 ^= $v2;
 102         $v2 = $v2.rotate_left(32);
 103     }};
 104 }
 105
 106 /// Loads an integer of the desired type from a byte stream, in LE order. Uses
 107 /// `copy_nonoverlapping` to let the compiler generate the most efficient way
 108 /// to load it from a possibly unaligned address.
 109 ///
 110 /// Unsafe because: unchecked indexing at i..i+size_of(int_ty)
 111 macro_rules! load_int_le {
 112     ($buf:expr, $i:expr, $int_ty:ident) => {{
 113         debug_assert!($i + mem::size_of::<$int_ty>() <= $buf.len());
 114         let mut data = 0 as $int_ty;
 115         ptr::copy_nonoverlapping(
 116             $buf.get_unchecked($i),
 117             &mut data as *mut _ as *mut u8,
 118             mem::size_of::<$int_ty>(),
 119         );
 120         data.to_le()
 121     }};
 122 }
 123
 124 /// Loads an u64 using up to 7 bytes of a byte slice.
 125 ///
 126 /// Unsafe because: unchecked indexing at start..start+len
 127 #[inline]
 128 unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
 129     debug_assert!(len < 8);
 130     let mut i = 0; // current byte index (from LSB) in the output u64
 131     let mut out = 0;
 132     if i + 3 < len {
 133         out = load_int_le!(buf, start + i, u32) as u64;
 134         i += 4;
 135     }
 136     if i + 1 < len {
 137         out |= (load_int_le!(buf, start + i, u16) as u64) << (i * 8);
 138         i += 2
 139     }
 140     if i < len {
 141         out |= (*buf.get_unchecked(start + i) as u64) << (i * 8);
 142         i += 1;
 143     }
 144     debug_assert_eq!(i, len);
 145     out
 146 }
 147
 148 impl SipHasher {
 149     /// Creates a new `SipHasher` with the two initial keys set to 0.
 150     #[inline]
 151     #[stable(feature = "rust1", since = "1.0.0")]
 152     #[rustc_deprecated(
 153         since = "1.13.0",
 154         reason = "use `std::collections::hash_map::DefaultHasher` instead"
 155     )]
 156     pub fn new() -> SipHasher {
 157         SipHasher::new_with_keys(0, 0)
 158     }
 159
 160     /// Creates a `SipHasher` that is keyed off the provided keys.
 161     #[inline]
 162     #[stable(feature = "rust1", since = "1.0.0")]
 163     #[rustc_deprecated(
 164         since = "1.13.0",
 165         reason = "use `std::collections::hash_map::DefaultHasher` instead"
 166     )]
 167     pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher {
 168         SipHasher(SipHasher24 { hasher: Hasher::new_with_keys(key0, key1) })
 169     }
 170 }
 171
 172 impl SipHasher13 {
 173     /// Creates a new `SipHasher13` with the two initial keys set to 0.
 174     #[inline]
 175     #[unstable(feature = "hashmap_internals", issue = "0")]
 176     #[rustc_deprecated(
 177         since = "1.13.0",
 178         reason = "use `std::collections::hash_map::DefaultHasher` instead"
 179     )]
 180     pub fn new() -> SipHasher13 {
 181         SipHasher13::new_with_keys(0, 0)
 182     }
 183
 184     /// Creates a `SipHasher13` that is keyed off the provided keys.
 185     #[inline]
 186     #[unstable(feature = "hashmap_internals", issue = "0")]
 187     #[rustc_deprecated(
 188         since = "1.13.0",
 189         reason = "use `std::collections::hash_map::DefaultHasher` instead"
 190     )]
 191     pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher13 {
 192         SipHasher13 { hasher: Hasher::new_with_keys(key0, key1) }
 193     }
 194 }
 195
 196 impl<S: Sip> Hasher<S> {
 197     #[inline]
 198     fn new_with_keys(key0: u64, key1: u64) -> Hasher<S> {
 199         let mut state = Hasher {
 200             k0: key0,
 201             k1: key1,
 202             length: 0,
 203             state: State { v0: 0, v1: 0, v2: 0, v3: 0 },
 204             tail: 0,
 205             ntail: 0,
 206             _marker: PhantomData,
 207         };
 208         state.reset();
 209         state
 210     }
 211
 212     #[inline]
 213     fn reset(&mut self) {
 214         self.length = 0;
 215         self.state.v0 = self.k0 ^ 0x736f6d6570736575;
 216         self.state.v1 = self.k1 ^ 0x646f72616e646f6d;
 217         self.state.v2 = self.k0 ^ 0x6c7967656e657261;
 218         self.state.v3 = self.k1 ^ 0x7465646279746573;
 219         self.ntail = 0;
 220     }
 221
 222     // Specialized write function that is only valid for buffers with len <= 8.
 223     // It's used to force inlining of write_u8 and write_usize, those would normally be inlined
 224     // except for composite types (that includes slices and str hashing because of delimiter).
 225     // Without this extra push the compiler is very reluctant to inline delimiter writes,
 226     // degrading performance substantially for the most common use cases.
 227     #[inline]
 228     fn short_write(&mut self, msg: &[u8]) {
 229         debug_assert!(msg.len() <= 8);
 230         let length = msg.len();
 231         self.length += length;
 232
 233         let needed = 8 - self.ntail;
 234         let fill = cmp::min(length, needed);
 235         if fill == 8 {
 236             self.tail = unsafe { load_int_le!(msg, 0, u64) };
 237         } else {
 238             self.tail |= unsafe { u8to64_le(msg, 0, fill) } << (8 * self.ntail);
 239             if length < needed {
 240                 self.ntail += length;
 241                 return;
 242             }
 243         }
 244         self.state.v3 ^= self.tail;
 245         S::c_rounds(&mut self.state);
 246         self.state.v0 ^= self.tail;
 247
 248         // Buffered tail is now flushed, process new input.
 249         self.ntail = length - needed;
 250         self.tail = unsafe { u8to64_le(msg, needed, self.ntail) };
 251     }
 252 }
 253
 254 #[stable(feature = "rust1", since = "1.0.0")]
 255 impl super::Hasher for SipHasher {
 256     #[inline]
 257     fn write(&mut self, msg: &[u8]) {
 258         self.0.hasher.write(msg)
 259     }
 260
 261     #[inline]
 262     fn finish(&self) -> u64 {
 263         self.0.hasher.finish()
 264     }
 265 }
 266
 267 #[unstable(feature = "hashmap_internals", issue = "0")]
 268 impl super::Hasher for SipHasher13 {
 269     #[inline]
 270     fn write(&mut self, msg: &[u8]) {
 271         self.hasher.write(msg)
 272     }
 273
 274     #[inline]
 275     fn finish(&self) -> u64 {
 276         self.hasher.finish()
 277     }
 278 }
 279
 280 impl<S: Sip> super::Hasher for Hasher<S> {
 281     // see short_write comment for explanation
 282     #[inline]
 283     fn write_usize(&mut self, i: usize) {
 284         let bytes = unsafe {
 285             crate::slice::from_raw_parts(&i as *const usize as *const u8, mem::size_of::<usize>())
 286         };
 287         self.short_write(bytes);
 288     }
 289
 290     // see short_write comment for explanation
 291     #[inline]
 292     fn write_u8(&mut self, i: u8) {
 293         self.short_write(&[i]);
 294     }
 295
 296     #[inline]
 297     fn write(&mut self, msg: &[u8]) {
 298         let length = msg.len();
 299         self.length += length;
 300
 301         let mut needed = 0;
 302
 303         if self.ntail != 0 {
 304             needed = 8 - self.ntail;
 305             self.tail |= unsafe { u8to64_le(msg, 0, cmp::min(length, needed)) } << 8 * self.ntail;
 306             if length < needed {
 307                 self.ntail += length;
 308                 return;
 309             } else {
 310                 self.state.v3 ^= self.tail;
 311                 S::c_rounds(&mut self.state);
 312                 self.state.v0 ^= self.tail;
 313                 self.ntail = 0;
 314             }
 315         }
 316
 317         // Buffered tail is now flushed, process new input.
 318         let len = length - needed;
 319         let left = len & 0x7;
 320
 321         let mut i = needed;
 322         while i < len - left {
 323             let mi = unsafe { load_int_le!(msg, i, u64) };
 324
 325             self.state.v3 ^= mi;
 326             S::c_rounds(&mut self.state);
 327             self.state.v0 ^= mi;
 328
 329             i += 8;
 330         }
 331
 332         self.tail = unsafe { u8to64_le(msg, i, left) };
 333         self.ntail = left;
 334     }
 335
 336     #[inline]
 337     fn finish(&self) -> u64 {
 338         let mut state = self.state;
 339
 340         let b: u64 = ((self.length as u64 & 0xff) << 56) | self.tail;
 341
 342         state.v3 ^= b;
 343         S::c_rounds(&mut state);
 344         state.v0 ^= b;
 345
 346         state.v2 ^= 0xff;
 347         S::d_rounds(&mut state);
 348
 349         state.v0 ^ state.v1 ^ state.v2 ^ state.v3
 350     }
 351 }
 352
 353 impl<S: Sip> Clone for Hasher<S> {
 354     #[inline]
 355     fn clone(&self) -> Hasher<S> {
 356         Hasher {
 357             k0: self.k0,
 358             k1: self.k1,
 359             length: self.length,
 360             state: self.state,
 361             tail: self.tail,
 362             ntail: self.ntail,
 363             _marker: self._marker,
 364         }
 365     }
 366 }
 367
 368 impl<S: Sip> Default for Hasher<S> {
 369     /// Creates a `Hasher<S>` with the two initial keys set to 0.
 370     #[inline]
 371     fn default() -> Hasher<S> {
 372         Hasher::new_with_keys(0, 0)
 373     }
 374 }
 375
 376 #[doc(hidden)]
 377 trait Sip {
 378     fn c_rounds(_: &mut State);
 379     fn d_rounds(_: &mut State);
 380 }
 381
 382 #[derive(Debug, Clone, Default)]
 383 struct Sip13Rounds;
 384
 385 impl Sip for Sip13Rounds {
 386     #[inline]
 387     fn c_rounds(state: &mut State) {
 388         compress!(state);
 389     }
 390
 391     #[inline]
 392     fn d_rounds(state: &mut State) {
 393         compress!(state);
 394         compress!(state);
 395         compress!(state);
 396     }
 397 }
 398
 399 #[derive(Debug, Clone, Default)]
 400 struct Sip24Rounds;
 401
 402 impl Sip for Sip24Rounds {
 403     #[inline]
 404     fn c_rounds(state: &mut State) {
 405         compress!(state);
 406         compress!(state);
 407     }
 408
 409     #[inline]
 410     fn d_rounds(state: &mut State) {
 411         compress!(state);
 412         compress!(state);
 413         compress!(state);
 414         compress!(state);
 415     }
 416 }