1use core::hash::Hash;
2cfg_if::cfg_if! {
3 if #[cfg(any(
4 all(any(target_arch = "x86", target_arch = "x86_64"), target_feature = "aes", not(miri)),
5 all(feature = "nightly-arm-aes", target_arch = "aarch64", target_feature = "aes", not(miri)),
6 all(feature = "nightly-arm-aes", target_arch = "arm", target_feature = "aes", not(miri)),
7 ))] {
8 use crate::aes_hash::*;
9 } else {
10 use crate::fallback_hash::*;
11 }
12}
13cfg_if::cfg_if! {
14 if #[cfg(feature = "specialize")]{
15 use crate::BuildHasherExt;
16 }
17}
18cfg_if::cfg_if! {
19 if #[cfg(feature = "std")] {
20 extern crate std as alloc;
21 } else {
22 extern crate alloc;
23 }
24}
25
26#[cfg(feature = "atomic-polyfill")]
27use atomic_polyfill as atomic;
28#[cfg(not(feature = "atomic-polyfill"))]
29use core::sync::atomic;
30
31use alloc::boxed::Box;
32use atomic::{AtomicUsize, Ordering};
33use core::any::{Any, TypeId};
34use core::fmt;
35use core::hash::BuildHasher;
36use core::hash::Hasher;
37
38pub(crate) const PI: [u64; 4] = [
39 0x243f_6a88_85a3_08d3,
40 0x1319_8a2e_0370_7344,
41 0xa409_3822_299f_31d0,
42 0x082e_fa98_ec4e_6c89,
43];
44
45pub(crate) const PI2: [u64; 4] = [
46 0x4528_21e6_38d0_1377,
47 0xbe54_66cf_34e9_0c6c,
48 0xc0ac_29b7_c97c_50dd,
49 0x3f84_d5b5_b547_0917,
50];
51
52cfg_if::cfg_if! {
53 if #[cfg(all(feature = "compile-time-rng", any(test, fuzzing)))] {
54 #[inline]
55 fn get_fixed_seeds() -> &'static [[u64; 4]; 2] {
56 use const_random::const_random;
57
58 const RAND: [[u64; 4]; 2] = [
59 [
60 const_random!(u64),
61 const_random!(u64),
62 const_random!(u64),
63 const_random!(u64),
64 ], [
65 const_random!(u64),
66 const_random!(u64),
67 const_random!(u64),
68 const_random!(u64),
69 ]
70 ];
71 &RAND
72 }
73 } else if #[cfg(all(feature = "runtime-rng", not(fuzzing)))] {
74 #[inline]
75 fn get_fixed_seeds() -> &'static [[u64; 4]; 2] {
76 use crate::convert::Convert;
77
78 static SEEDS: OnceBox<[[u64; 4]; 2]> = OnceBox::new();
79
80 SEEDS.get_or_init(|| {
81 let mut result: [u8; 64] = [0; 64];
82 getrandom::getrandom(&mut result).expect("getrandom::getrandom() failed.");
83 Box::new(result.convert())
84 })
85 }
86 } else if #[cfg(feature = "compile-time-rng")] {
87 #[inline]
88 fn get_fixed_seeds() -> &'static [[u64; 4]; 2] {
89 use const_random::const_random;
90
91 const RAND: [[u64; 4]; 2] = [
92 [
93 const_random!(u64),
94 const_random!(u64),
95 const_random!(u64),
96 const_random!(u64),
97 ], [
98 const_random!(u64),
99 const_random!(u64),
100 const_random!(u64),
101 const_random!(u64),
102 ]
103 ];
104 &RAND
105 }
106 } else {
107 #[inline]
108 fn get_fixed_seeds() -> &'static [[u64; 4]; 2] {
109 &[PI, PI2]
110 }
111 }
112}
113
114cfg_if::cfg_if! {
115 if #[cfg(not(all(target_arch = "arm", target_os = "none")))] {
116 use once_cell::race::OnceBox;
117
118 static RAND_SOURCE: OnceBox<Box<dyn RandomSource + Send + Sync>> = OnceBox::new();
119 }
120}
121/// A supplier of Randomness used for different hashers.
122/// See [set_random_source].
123///
124/// If [set_random_source] aHash will default to the best available source of randomness.
125/// In order this is:
126/// 1. OS provided random number generator (available if the `runtime-rng` flag is enabled which it is by default) - This should be very strong.
127/// 2. Strong compile time random numbers used to permute a static "counter". (available if `compile-time-rng` is enabled.
128/// __Enabling this is recommended if `runtime-rng` is not possible__)
129/// 3. A static counter that adds the memory address of each [RandomState] created permuted with fixed constants.
130/// (Similar to above but with fixed keys) - This is the weakest option. The strength of this heavily depends on whether or not ASLR is enabled.
131/// (Rust enables ASLR by default)
132pub trait RandomSource {
133 fn gen_hasher_seed(&self) -> usize;
134}
135
136struct DefaultRandomSource {
137 counter: AtomicUsize,
138}
139
140impl DefaultRandomSource {
141 fn new() -> DefaultRandomSource {
142 DefaultRandomSource {
143 counter: AtomicUsize::new(&PI as *const _ as usize),
144 }
145 }
146
147 #[cfg(all(target_arch = "arm", target_os = "none"))]
148 const fn default() -> DefaultRandomSource {
149 DefaultRandomSource {
150 counter: AtomicUsize::new(PI[3] as usize),
151 }
152 }
153}
154
155impl RandomSource for DefaultRandomSource {
156 cfg_if::cfg_if! {
157 if #[cfg(all(target_arch = "arm", target_os = "none"))] {
158 fn gen_hasher_seed(&self) -> usize {
159 let stack = self as *const _ as usize;
160 let previous = self.counter.load(Ordering::Relaxed);
161 let new = previous.wrapping_add(stack);
162 self.counter.store(new, Ordering::Relaxed);
163 new
164 }
165 } else {
166 fn gen_hasher_seed(&self) -> usize {
167 let stack = self as *const _ as usize;
168 self.counter.fetch_add(stack, Ordering::Relaxed)
169 }
170 }
171 }
172}
173
174cfg_if::cfg_if! {
175 if #[cfg(all(target_arch = "arm", target_os = "none"))] {
176 #[inline]
177 fn get_src() -> &'static dyn RandomSource {
178 static RAND_SOURCE: DefaultRandomSource = DefaultRandomSource::default();
179 &RAND_SOURCE
180 }
181 } else {
182 /// Provides an optional way to manually supply a source of randomness for Hasher keys.
183 ///
184 /// The provided [RandomSource] will be used to be used as a source of randomness by [RandomState] to generate new states.
185 /// If this method is not invoked the standard source of randomness is used as described in the Readme.
186 ///
187 /// The source of randomness can only be set once, and must be set before the first RandomState is created.
188 /// If the source has already been specified `Err` is returned with a `bool` indicating if the set failed because
189 /// method was previously invoked (true) or if the default source is already being used (false).
190 #[cfg(not(all(target_arch = "arm", target_os = "none")))]
191 pub fn set_random_source(source: impl RandomSource + Send + Sync + 'static) -> Result<(), bool> {
192 RAND_SOURCE.set(Box::new(Box::new(source))).map_err(|s| s.as_ref().type_id() != TypeId::of::<&DefaultRandomSource>())
193 }
194
195 #[inline]
196 fn get_src() -> &'static dyn RandomSource {
197 RAND_SOURCE.get_or_init(|| Box::new(Box::new(DefaultRandomSource::new()))).as_ref()
198 }
199 }
200}
201
202/// Provides a [Hasher] factory. This is typically used (e.g. by [HashMap]) to create
203/// [AHasher]s in order to hash the keys of the map. See `build_hasher` below.
204///
205/// [build_hasher]: ahash::
206/// [Hasher]: std::hash::Hasher
207/// [BuildHasher]: std::hash::BuildHasher
208/// [HashMap]: std::collections::HashMap
209///
210/// There are multiple constructors each is documented in more detail below:
211///
212/// | Constructor | Dynamically random? | Seed |
213/// |---------------|---------------------|------|
214/// |`new` | Each instance unique|_[RandomSource]_|
215/// |`generate_with`| Each instance unique|`u64` x 4 + [RandomSource]|
216/// |`with_seed` | Fixed per process |`u64` + static random number|
217/// |`with_seeds` | Fixed |`u64` x 4|
218///
219#[derive(Clone)]
220pub struct RandomState {
221 pub(crate) k0: u64,
222 pub(crate) k1: u64,
223 pub(crate) k2: u64,
224 pub(crate) k3: u64,
225}
226
227impl fmt::Debug for RandomState {
228 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
229 f.pad("RandomState { .. }")
230 }
231}
232
233impl RandomState {
234 /// Create a new `RandomState` `BuildHasher` using random keys.
235 ///
236 /// Each instance will have a unique set of keys derived from [RandomSource].
237 ///
238 #[inline]
239 pub fn new() -> RandomState {
240 let src = get_src();
241 let fixed = get_fixed_seeds();
242 Self::from_keys(&fixed[0], &fixed[1], src.gen_hasher_seed())
243 }
244
245 /// Create a new `RandomState` `BuildHasher` based on the provided seeds, but in such a way
246 /// that each time it is called the resulting state will be different and of high quality.
247 /// This allows fixed constant or poor quality seeds to be provided without the problem of different
248 /// `BuildHasher`s being identical or weak.
249 ///
250 /// This is done via permuting the provided values with the value of a static counter and memory address.
251 /// (This makes this method somewhat more expensive than `with_seeds` below which does not do this).
252 ///
253 /// The provided values (k0-k3) do not need to be of high quality but they should not all be the same value.
254 #[inline]
255 pub fn generate_with(k0: u64, k1: u64, k2: u64, k3: u64) -> RandomState {
256 let src = get_src();
257 let fixed = get_fixed_seeds();
258 RandomState::from_keys(&fixed[0], &[k0, k1, k2, k3], src.gen_hasher_seed())
259 }
260
261 fn from_keys(a: &[u64; 4], b: &[u64; 4], c: usize) -> RandomState {
262 let &[k0, k1, k2, k3] = a;
263 let mut hasher = AHasher::from_random_state(&RandomState { k0, k1, k2, k3 });
264 hasher.write_usize(c);
265 let mix = |l: u64, r: u64| {
266 let mut h = hasher.clone();
267 h.write_u64(l);
268 h.write_u64(r);
269 h.finish()
270 };
271 RandomState {
272 k0: mix(b[0], b[2]),
273 k1: mix(b[1], b[3]),
274 k2: mix(b[2], b[1]),
275 k3: mix(b[3], b[0]),
276 }
277 }
278
279 /// Internal. Used by Default.
280 #[inline]
281 pub(crate) fn with_fixed_keys() -> RandomState {
282 let [k0, k1, k2, k3] = get_fixed_seeds()[0];
283 RandomState { k0, k1, k2, k3 }
284 }
285
286 /// Build a `RandomState` from a single key. The provided key does not need to be of high quality,
287 /// but all `RandomState`s created from the same key will produce identical hashers.
288 /// (In contrast to `generate_with` above)
289 ///
290 /// This allows for explicitly setting the seed to be used.
291 ///
292 /// Note: This method does not require the provided seed to be strong.
293 #[inline]
294 pub fn with_seed(key: usize) -> RandomState {
295 let fixed = get_fixed_seeds();
296 RandomState::from_keys(&fixed[0], &fixed[1], key)
297 }
298
299 /// Allows for explicitly setting the seeds to used.
300 /// All `RandomState`s created with the same set of keys key will produce identical hashers.
301 /// (In contrast to `generate_with` above)
302 ///
303 /// Note: If DOS resistance is desired one of these should be a decent quality random number.
304 /// If 4 high quality random number are not cheaply available this method is robust against 0s being passed for
305 /// one or more of the parameters or the same value being passed for more than one parameter.
306 /// It is recommended to pass numbers in order from highest to lowest quality (if there is any difference).
307 #[inline]
308 pub const fn with_seeds(k0: u64, k1: u64, k2: u64, k3: u64) -> RandomState {
309 RandomState {
310 k0: k0 ^ PI2[0],
311 k1: k1 ^ PI2[1],
312 k2: k2 ^ PI2[2],
313 k3: k3 ^ PI2[3],
314 }
315 }
316
317 /// Calculates the hash of a single value. This provides a more convenient (and faster) way to obtain a hash:
318 /// For example:
319 #[cfg_attr(
320 feature = "std",
321 doc = r##" # Examples
322```
323 use std::hash::BuildHasher;
324 use ahash::RandomState;
325
326 let hash_builder = RandomState::new();
327 let hash = hash_builder.hash_one("Some Data");
328```
329 "##
330 )]
331 /// This is similar to:
332 #[cfg_attr(
333 feature = "std",
334 doc = r##" # Examples
335```
336 use std::hash::{BuildHasher, Hash, Hasher};
337 use ahash::RandomState;
338
339 let hash_builder = RandomState::new();
340 let mut hasher = hash_builder.build_hasher();
341 "Some Data".hash(&mut hasher);
342 let hash = hasher.finish();
343```
344 "##
345 )]
346 /// (Note that these two ways to get a hash may not produce the same value for the same data)
347 ///
348 /// This is intended as a convenience for code which *consumes* hashes, such
349 /// as the implementation of a hash table or in unit tests that check
350 /// whether a custom [`Hash`] implementation behaves as expected.
351 ///
352 /// This must not be used in any code which *creates* hashes, such as in an
353 /// implementation of [`Hash`]. The way to create a combined hash of
354 /// multiple values is to call [`Hash::hash`] multiple times using the same
355 /// [`Hasher`], not to call this method repeatedly and combine the results.
356 #[inline]
357 pub fn hash_one<T: Hash>(&self, x: T) -> u64
358 where
359 Self: Sized,
360 {
361 use crate::specialize::CallHasher;
362 T::get_hash(&x, self)
363 }
364}
365
366/// Creates an instance of RandomState using keys obtained from the random number generator.
367/// Each instance created in this way will have a unique set of keys. (But the resulting instance
368/// can be used to create many hashers each or which will have the same keys.)
369///
370/// This is the same as [RandomState::new()]
371///
372/// NOTE: For safety this trait impl is only available available if either of the flags `runtime-rng` (on by default) or
373/// `compile-time-rng` are enabled. This is to prevent weakly keyed maps from being accidentally created. Instead one of
374/// constructors for [RandomState] must be used.
375#[cfg(any(feature = "compile-time-rng", feature = "runtime-rng", feature = "no-rng"))]
376impl Default for RandomState {
377 #[inline]
378 fn default() -> Self {
379 Self::new()
380 }
381}
382
383impl BuildHasher for RandomState {
384 type Hasher = AHasher;
385
386 /// Constructs a new [AHasher] with keys based on this [RandomState] object.
387 /// This means that two different [RandomState]s will will generate
388 /// [AHasher]s that will return different hashcodes, but [Hasher]s created from the same [BuildHasher]
389 /// will generate the same hashes for the same input data.
390 ///
391 #[cfg_attr(
392 feature = "std",
393 doc = r##" # Examples
394```
395 use ahash::{AHasher, RandomState};
396 use std::hash::{Hasher, BuildHasher};
397
398 let build_hasher = RandomState::new();
399 let mut hasher_1 = build_hasher.build_hasher();
400 let mut hasher_2 = build_hasher.build_hasher();
401
402 hasher_1.write_u32(1234);
403 hasher_2.write_u32(1234);
404
405 assert_eq!(hasher_1.finish(), hasher_2.finish());
406
407 let other_build_hasher = RandomState::new();
408 let mut different_hasher = other_build_hasher.build_hasher();
409 different_hasher.write_u32(1234);
410 assert_ne!(different_hasher.finish(), hasher_1.finish());
411```
412 "##
413 )]
414 /// [Hasher]: std::hash::Hasher
415 /// [BuildHasher]: std::hash::BuildHasher
416 /// [HashMap]: std::collections::HashMap
417 #[inline]
418 fn build_hasher(&self) -> AHasher {
419 AHasher::from_random_state(self)
420 }
421
422 /// Calculates the hash of a single value. This provides a more convenient (and faster) way to obtain a hash:
423 /// For example:
424 #[cfg_attr(
425 feature = "std",
426 doc = r##" # Examples
427```
428 use std::hash::BuildHasher;
429 use ahash::RandomState;
430
431 let hash_builder = RandomState::new();
432 let hash = hash_builder.hash_one("Some Data");
433```
434 "##
435 )]
436 /// This is similar to:
437 #[cfg_attr(
438 feature = "std",
439 doc = r##" # Examples
440```
441 use std::hash::{BuildHasher, Hash, Hasher};
442 use ahash::RandomState;
443
444 let hash_builder = RandomState::new();
445 let mut hasher = hash_builder.build_hasher();
446 "Some Data".hash(&mut hasher);
447 let hash = hasher.finish();
448```
449 "##
450 )]
451 /// (Note that these two ways to get a hash may not produce the same value for the same data)
452 ///
453 /// This is intended as a convenience for code which *consumes* hashes, such
454 /// as the implementation of a hash table or in unit tests that check
455 /// whether a custom [`Hash`] implementation behaves as expected.
456 ///
457 /// This must not be used in any code which *creates* hashes, such as in an
458 /// implementation of [`Hash`]. The way to create a combined hash of
459 /// multiple values is to call [`Hash::hash`] multiple times using the same
460 /// [`Hasher`], not to call this method repeatedly and combine the results.
461 #[cfg(feature = "specialize")]
462 #[inline]
463 fn hash_one<T: Hash>(&self, x: T) -> u64 {
464 RandomState::hash_one(self, x)
465 }
466}
467
468#[cfg(feature = "specialize")]
469impl BuildHasherExt for RandomState {
470 #[inline]
471 fn hash_as_u64<T: Hash + ?Sized>(&self, value: &T) -> u64 {
472 let mut hasher = AHasherU64 {
473 buffer: self.k1,
474 pad: self.k0,
475 };
476 value.hash(&mut hasher);
477 hasher.finish()
478 }
479
480 #[inline]
481 fn hash_as_fixed_length<T: Hash + ?Sized>(&self, value: &T) -> u64 {
482 let mut hasher = AHasherFixed(self.build_hasher());
483 value.hash(&mut hasher);
484 hasher.finish()
485 }
486
487 #[inline]
488 fn hash_as_str<T: Hash + ?Sized>(&self, value: &T) -> u64 {
489 let mut hasher = AHasherStr(self.build_hasher());
490 value.hash(&mut hasher);
491 hasher.finish()
492 }
493}
494
495#[cfg(test)]
496mod test {
497 use super::*;
498
499 #[test]
500 fn test_unique() {
501 let a = RandomState::generate_with(1, 2, 3, 4);
502 let b = RandomState::generate_with(1, 2, 3, 4);
503 assert_ne!(a.build_hasher().finish(), b.build_hasher().finish());
504 }
505
506 #[cfg(all(feature = "runtime-rng", not(all(feature = "compile-time-rng", test))))]
507 #[test]
508 fn test_not_pi() {
509 assert_ne!(PI, get_fixed_seeds()[0]);
510 }
511
512 #[cfg(all(feature = "compile-time-rng", any(not(feature = "runtime-rng"), test)))]
513 #[test]
514 fn test_not_pi_const() {
515 assert_ne!(PI, get_fixed_seeds()[0]);
516 }
517
518 #[cfg(all(not(feature = "runtime-rng"), not(feature = "compile-time-rng")))]
519 #[test]
520 fn test_pi() {
521 assert_eq!(PI, get_fixed_seeds()[0]);
522 }
523
524 #[test]
525 fn test_with_seeds_const() {
526 const _CONST_RANDOM_STATE: RandomState = RandomState::with_seeds(17, 19, 21, 23);
527 }
528}
529