1//===-- llvm/ADT/Hashing.h - Utilities for hashing --------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the newly proposed standard C++ interfaces for hashing
10// arbitrary data and building hash functions for user-defined types. This
11// interface was originally proposed in N3333[1] and is currently under review
12// for inclusion in a future TR and/or standard.
13//
14// The primary interfaces provide are comprised of one type and three functions:
15//
16// -- 'hash_code' class is an opaque type representing the hash code for some
17// data. It is the intended product of hashing, and can be used to implement
18// hash tables, checksumming, and other common uses of hashes. It is not an
19// integer type (although it can be converted to one) because it is risky
20// to assume much about the internals of a hash_code. In particular, each
21// execution of the program has a high probability of producing a different
22// hash_code for a given input. Thus their values are not stable to save or
23// persist, and should only be used during the execution for the
24// construction of hashing datastructures.
25//
26// -- 'hash_value' is a function designed to be overloaded for each
27// user-defined type which wishes to be used within a hashing context. It
28// should be overloaded within the user-defined type's namespace and found
29// via ADL. Overloads for primitive types are provided by this library.
30//
31// -- 'hash_combine' and 'hash_combine_range' are functions designed to aid
32// programmers in easily and intuitively combining a set of data into
33// a single hash_code for their object. They should only logically be used
34// within the implementation of a 'hash_value' routine or similar context.
35//
36// Note that 'hash_combine_range' contains very special logic for hashing
37// a contiguous array of integers or pointers. This logic is *extremely* fast,
38// on a modern Intel "Gainestown" Xeon (Nehalem uarch) @2.2 GHz, these were
39// benchmarked at over 6.5 GiB/s for large keys, and <20 cycles/hash for keys
40// under 32-bytes.
41//
42//===----------------------------------------------------------------------===//
43
44#ifndef LLVM_ADT_HASHING_H
45#define LLVM_ADT_HASHING_H
46
47#include "llvm/Support/DataTypes.h"
48#include "llvm/Support/ErrorHandling.h"
49#include "llvm/Support/SwapByteOrder.h"
50#include "llvm/Support/type_traits.h"
51#include <algorithm>
52#include <cassert>
53#include <cstring>
54#include <optional>
55#include <string>
56#include <tuple>
57#include <utility>
58
59namespace llvm {
60template <typename T, typename Enable> struct DenseMapInfo;
61
62/// An opaque object representing a hash code.
63///
64/// This object represents the result of hashing some entity. It is intended to
65/// be used to implement hashtables or other hashing-based data structures.
66/// While it wraps and exposes a numeric value, this value should not be
67/// trusted to be stable or predictable across processes or executions.
68///
69/// In order to obtain the hash_code for an object 'x':
70/// \code
71/// using llvm::hash_value;
72/// llvm::hash_code code = hash_value(x);
73/// \endcode
74class hash_code {
75 size_t value;
76
77public:
78 /// Default construct a hash_code.
79 /// Note that this leaves the value uninitialized.
80 hash_code() = default;
81
82 /// Form a hash code directly from a numerical value.
83 hash_code(size_t value) : value(value) {}
84
85 /// Convert the hash code to its numerical value for use.
86 /*explicit*/ operator size_t() const { return value; }
87
88 friend bool operator==(const hash_code &lhs, const hash_code &rhs) {
89 return lhs.value == rhs.value;
90 }
91 friend bool operator!=(const hash_code &lhs, const hash_code &rhs) {
92 return lhs.value != rhs.value;
93 }
94
95 /// Allow a hash_code to be directly run through hash_value.
96 friend size_t hash_value(const hash_code &code) { return code.value; }
97};
98
99/// Compute a hash_code for any integer value.
100///
101/// Note that this function is intended to compute the same hash_code for
102/// a particular value without regard to the pre-promotion type. This is in
103/// contrast to hash_combine which may produce different hash_codes for
104/// differing argument types even if they would implicit promote to a common
105/// type without changing the value.
106template <typename T>
107std::enable_if_t<is_integral_or_enum<T>::value, hash_code> hash_value(T value);
108
109/// Compute a hash_code for a pointer's address.
110///
111/// N.B.: This hashes the *address*. Not the value and not the type.
112template <typename T> hash_code hash_value(const T *ptr);
113
114/// Compute a hash_code for a pair of objects.
115template <typename T, typename U>
116hash_code hash_value(const std::pair<T, U> &arg);
117
118/// Compute a hash_code for a tuple.
119template <typename... Ts>
120hash_code hash_value(const std::tuple<Ts...> &arg);
121
122/// Compute a hash_code for a standard string.
123template <typename T>
124hash_code hash_value(const std::basic_string<T> &arg);
125
126/// Compute a hash_code for a standard string.
127template <typename T> hash_code hash_value(const std::optional<T> &arg);
128
129/// Override the execution seed with a fixed value.
130///
131/// This hashing library uses a per-execution seed designed to change on each
132/// run with high probability in order to ensure that the hash codes are not
133/// attackable and to ensure that output which is intended to be stable does
134/// not rely on the particulars of the hash codes produced.
135///
136/// That said, there are use cases where it is important to be able to
137/// reproduce *exactly* a specific behavior. To that end, we provide a function
138/// which will forcibly set the seed to a fixed value. This must be done at the
139/// start of the program, before any hashes are computed. Also, it cannot be
140/// undone. This makes it thread-hostile and very hard to use outside of
141/// immediately on start of a simple program designed for reproducible
142/// behavior.
143void set_fixed_execution_hash_seed(uint64_t fixed_value);
144
145
146// All of the implementation details of actually computing the various hash
147// code values are held within this namespace. These routines are included in
148// the header file mainly to allow inlining and constant propagation.
149namespace hashing {
150namespace detail {
151
152inline uint64_t fetch64(const char *p) {
153 uint64_t result;
154 memcpy(dest: &result, src: p, n: sizeof(result));
155 if (sys::IsBigEndianHost)
156 sys::swapByteOrder(Value&: result);
157 return result;
158}
159
160inline uint32_t fetch32(const char *p) {
161 uint32_t result;
162 memcpy(dest: &result, src: p, n: sizeof(result));
163 if (sys::IsBigEndianHost)
164 sys::swapByteOrder(Value&: result);
165 return result;
166}
167
168/// Some primes between 2^63 and 2^64 for various uses.
169static constexpr uint64_t k0 = 0xc3a5c85c97cb3127ULL;
170static constexpr uint64_t k1 = 0xb492b66fbe98f273ULL;
171static constexpr uint64_t k2 = 0x9ae16a3b2f90404fULL;
172static constexpr uint64_t k3 = 0xc949d7c7509e6557ULL;
173
174/// Bitwise right rotate.
175/// Normally this will compile to a single instruction, especially if the
176/// shift is a manifest constant.
177inline uint64_t rotate(uint64_t val, size_t shift) {
178 // Avoid shifting by 64: doing so yields an undefined result.
179 return shift == 0 ? val : ((val >> shift) | (val << (64 - shift)));
180}
181
182inline uint64_t shift_mix(uint64_t val) {
183 return val ^ (val >> 47);
184}
185
186inline uint64_t hash_16_bytes(uint64_t low, uint64_t high) {
187 // Murmur-inspired hashing.
188 const uint64_t kMul = 0x9ddfea08eb382d69ULL;
189 uint64_t a = (low ^ high) * kMul;
190 a ^= (a >> 47);
191 uint64_t b = (high ^ a) * kMul;
192 b ^= (b >> 47);
193 b *= kMul;
194 return b;
195}
196
197inline uint64_t hash_1to3_bytes(const char *s, size_t len, uint64_t seed) {
198 uint8_t a = s[0];
199 uint8_t b = s[len >> 1];
200 uint8_t c = s[len - 1];
201 uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);
202 uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2);
203 return shift_mix(val: y * k2 ^ z * k3 ^ seed) * k2;
204}
205
206inline uint64_t hash_4to8_bytes(const char *s, size_t len, uint64_t seed) {
207 uint64_t a = fetch32(p: s);
208 return hash_16_bytes(low: len + (a << 3), high: seed ^ fetch32(p: s + len - 4));
209}
210
211inline uint64_t hash_9to16_bytes(const char *s, size_t len, uint64_t seed) {
212 uint64_t a = fetch64(p: s);
213 uint64_t b = fetch64(p: s + len - 8);
214 return hash_16_bytes(low: seed ^ a, high: rotate(val: b + len, shift: len)) ^ b;
215}
216
217inline uint64_t hash_17to32_bytes(const char *s, size_t len, uint64_t seed) {
218 uint64_t a = fetch64(p: s) * k1;
219 uint64_t b = fetch64(p: s + 8);
220 uint64_t c = fetch64(p: s + len - 8) * k2;
221 uint64_t d = fetch64(p: s + len - 16) * k0;
222 return hash_16_bytes(low: llvm::rotr<uint64_t>(V: a - b, R: 43) +
223 llvm::rotr<uint64_t>(V: c ^ seed, R: 30) + d,
224 high: a + llvm::rotr<uint64_t>(V: b ^ k3, R: 20) - c + len + seed);
225}
226
227inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) {
228 uint64_t z = fetch64(p: s + 24);
229 uint64_t a = fetch64(p: s) + (len + fetch64(p: s + len - 16)) * k0;
230 uint64_t b = llvm::rotr<uint64_t>(V: a + z, R: 52);
231 uint64_t c = llvm::rotr<uint64_t>(V: a, R: 37);
232 a += fetch64(p: s + 8);
233 c += llvm::rotr<uint64_t>(V: a, R: 7);
234 a += fetch64(p: s + 16);
235 uint64_t vf = a + z;
236 uint64_t vs = b + llvm::rotr<uint64_t>(V: a, R: 31) + c;
237 a = fetch64(p: s + 16) + fetch64(p: s + len - 32);
238 z = fetch64(p: s + len - 8);
239 b = llvm::rotr<uint64_t>(V: a + z, R: 52);
240 c = llvm::rotr<uint64_t>(V: a, R: 37);
241 a += fetch64(p: s + len - 24);
242 c += llvm::rotr<uint64_t>(V: a, R: 7);
243 a += fetch64(p: s + len - 16);
244 uint64_t wf = a + z;
245 uint64_t ws = b + llvm::rotr<uint64_t>(V: a, R: 31) + c;
246 uint64_t r = shift_mix(val: (vf + ws) * k2 + (wf + vs) * k0);
247 return shift_mix(val: (seed ^ (r * k0)) + vs) * k2;
248}
249
250inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) {
251 if (length >= 4 && length <= 8)
252 return hash_4to8_bytes(s, len: length, seed);
253 if (length > 8 && length <= 16)
254 return hash_9to16_bytes(s, len: length, seed);
255 if (length > 16 && length <= 32)
256 return hash_17to32_bytes(s, len: length, seed);
257 if (length > 32)
258 return hash_33to64_bytes(s, len: length, seed);
259 if (length != 0)
260 return hash_1to3_bytes(s, len: length, seed);
261
262 return k2 ^ seed;
263}
264
265/// The intermediate state used during hashing.
266/// Currently, the algorithm for computing hash codes is based on CityHash and
267/// keeps 56 bytes of arbitrary state.
268struct hash_state {
269 uint64_t h0 = 0, h1 = 0, h2 = 0, h3 = 0, h4 = 0, h5 = 0, h6 = 0;
270
271 /// Create a new hash_state structure and initialize it based on the
272 /// seed and the first 64-byte chunk.
273 /// This effectively performs the initial mix.
274 static hash_state create(const char *s, uint64_t seed) {
275 hash_state state = {.h0: 0,
276 .h1: seed,
277 .h2: hash_16_bytes(low: seed, high: k1),
278 .h3: llvm::rotr<uint64_t>(V: seed ^ k1, R: 49),
279 .h4: seed * k1,
280 .h5: shift_mix(val: seed),
281 .h6: 0};
282 state.h6 = hash_16_bytes(low: state.h4, high: state.h5);
283 state.mix(s);
284 return state;
285 }
286
287 /// Mix 32-bytes from the input sequence into the 16-bytes of 'a'
288 /// and 'b', including whatever is already in 'a' and 'b'.
289 static void mix_32_bytes(const char *s, uint64_t &a, uint64_t &b) {
290 a += fetch64(p: s);
291 uint64_t c = fetch64(p: s + 24);
292 b = llvm::rotr<uint64_t>(V: b + a + c, R: 21);
293 uint64_t d = a;
294 a += fetch64(p: s + 8) + fetch64(p: s + 16);
295 b += llvm::rotr<uint64_t>(V: a, R: 44) + d;
296 a += c;
297 }
298
299 /// Mix in a 64-byte buffer of data.
300 /// We mix all 64 bytes even when the chunk length is smaller, but we
301 /// record the actual length.
302 void mix(const char *s) {
303 h0 = llvm::rotr<uint64_t>(V: h0 + h1 + h3 + fetch64(p: s + 8), R: 37) * k1;
304 h1 = llvm::rotr<uint64_t>(V: h1 + h4 + fetch64(p: s + 48), R: 42) * k1;
305 h0 ^= h6;
306 h1 += h3 + fetch64(p: s + 40);
307 h2 = llvm::rotr<uint64_t>(V: h2 + h5, R: 33) * k1;
308 h3 = h4 * k1;
309 h4 = h0 + h5;
310 mix_32_bytes(s, a&: h3, b&: h4);
311 h5 = h2 + h6;
312 h6 = h1 + fetch64(p: s + 16);
313 mix_32_bytes(s: s + 32, a&: h5, b&: h6);
314 std::swap(a&: h2, b&: h0);
315 }
316
317 /// Compute the final 64-bit hash code value based on the current
318 /// state and the length of bytes hashed.
319 uint64_t finalize(size_t length) {
320 return hash_16_bytes(low: hash_16_bytes(low: h3, high: h5) + shift_mix(val: h1) * k1 + h2,
321 high: hash_16_bytes(low: h4, high: h6) + shift_mix(val: length) * k1 + h0);
322 }
323};
324
325
326/// A global, fixed seed-override variable.
327///
328/// This variable can be set using the \see llvm::set_fixed_execution_seed
329/// function. See that function for details. Do not, under any circumstances,
330/// set or read this variable.
331extern uint64_t fixed_seed_override;
332
333inline uint64_t get_execution_seed() {
334 // FIXME: This needs to be a per-execution seed. This is just a placeholder
335 // implementation. Switching to a per-execution seed is likely to flush out
336 // instability bugs and so will happen as its own commit.
337 //
338 // However, if there is a fixed seed override set the first time this is
339 // called, return that instead of the per-execution seed.
340 const uint64_t seed_prime = 0xff51afd7ed558ccdULL;
341 static uint64_t seed = fixed_seed_override ? fixed_seed_override : seed_prime;
342 return seed;
343}
344
345
346/// Trait to indicate whether a type's bits can be hashed directly.
347///
348/// A type trait which is true if we want to combine values for hashing by
349/// reading the underlying data. It is false if values of this type must
350/// first be passed to hash_value, and the resulting hash_codes combined.
351//
352// FIXME: We want to replace is_integral_or_enum and is_pointer here with
353// a predicate which asserts that comparing the underlying storage of two
354// values of the type for equality is equivalent to comparing the two values
355// for equality. For all the platforms we care about, this holds for integers
356// and pointers, but there are platforms where it doesn't and we would like to
357// support user-defined types which happen to satisfy this property.
358template <typename T> struct is_hashable_data
359 : std::integral_constant<bool, ((is_integral_or_enum<T>::value ||
360 std::is_pointer<T>::value) &&
361 64 % sizeof(T) == 0)> {};
362
363// Special case std::pair to detect when both types are viable and when there
364// is no alignment-derived padding in the pair. This is a bit of a lie because
365// std::pair isn't truly POD, but it's close enough in all reasonable
366// implementations for our use case of hashing the underlying data.
367template <typename T, typename U> struct is_hashable_data<std::pair<T, U> >
368 : std::integral_constant<bool, (is_hashable_data<T>::value &&
369 is_hashable_data<U>::value &&
370 (sizeof(T) + sizeof(U)) ==
371 sizeof(std::pair<T, U>))> {};
372
373/// Helper to get the hashable data representation for a type.
374/// This variant is enabled when the type itself can be used.
375template <typename T>
376std::enable_if_t<is_hashable_data<T>::value, T>
377get_hashable_data(const T &value) {
378 return value;
379}
380/// Helper to get the hashable data representation for a type.
381/// This variant is enabled when we must first call hash_value and use the
382/// result as our data.
383template <typename T>
384std::enable_if_t<!is_hashable_data<T>::value, size_t>
385get_hashable_data(const T &value) {
386 using ::llvm::hash_value;
387 return hash_value(value);
388}
389
390/// Helper to store data from a value into a buffer and advance the
391/// pointer into that buffer.
392///
393/// This routine first checks whether there is enough space in the provided
394/// buffer, and if not immediately returns false. If there is space, it
395/// copies the underlying bytes of value into the buffer, advances the
396/// buffer_ptr past the copied bytes, and returns true.
397template <typename T>
398bool store_and_advance(char *&buffer_ptr, char *buffer_end, const T& value,
399 size_t offset = 0) {
400 size_t store_size = sizeof(value) - offset;
401 if (buffer_ptr + store_size > buffer_end)
402 return false;
403 const char *value_data = reinterpret_cast<const char *>(&value);
404 memcpy(dest: buffer_ptr, src: value_data + offset, n: store_size);
405 buffer_ptr += store_size;
406 return true;
407}
408
409/// Implement the combining of integral values into a hash_code.
410///
411/// This overload is selected when the value type of the iterator is
412/// integral. Rather than computing a hash_code for each object and then
413/// combining them, this (as an optimization) directly combines the integers.
414template <typename InputIteratorT>
415hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) {
416 const uint64_t seed = get_execution_seed();
417 char buffer[64], *buffer_ptr = buffer;
418 char *const buffer_end = std::end(arr&: buffer);
419 while (first != last && store_and_advance(buffer_ptr, buffer_end,
420 get_hashable_data(*first)))
421 ++first;
422 if (first == last)
423 return hash_short(s: buffer, length: buffer_ptr - buffer, seed);
424 assert(buffer_ptr == buffer_end);
425
426 hash_state state = state.create(s: buffer, seed);
427 size_t length = 64;
428 while (first != last) {
429 // Fill up the buffer. We don't clear it, which re-mixes the last round
430 // when only a partial 64-byte chunk is left.
431 buffer_ptr = buffer;
432 while (first != last && store_and_advance(buffer_ptr, buffer_end,
433 get_hashable_data(*first)))
434 ++first;
435
436 // Rotate the buffer if we did a partial fill in order to simulate doing
437 // a mix of the last 64-bytes. That is how the algorithm works when we
438 // have a contiguous byte sequence, and we want to emulate that here.
439 std::rotate(first: buffer, middle: buffer_ptr, last: buffer_end);
440
441 // Mix this chunk into the current state.
442 state.mix(s: buffer);
443 length += buffer_ptr - buffer;
444 };
445
446 return state.finalize(length);
447}
448
449/// Implement the combining of integral values into a hash_code.
450///
451/// This overload is selected when the value type of the iterator is integral
452/// and when the input iterator is actually a pointer. Rather than computing
453/// a hash_code for each object and then combining them, this (as an
454/// optimization) directly combines the integers. Also, because the integers
455/// are stored in contiguous memory, this routine avoids copying each value
456/// and directly reads from the underlying memory.
457template <typename ValueT>
458std::enable_if_t<is_hashable_data<ValueT>::value, hash_code>
459hash_combine_range_impl(ValueT *first, ValueT *last) {
460 const uint64_t seed = get_execution_seed();
461 const char *s_begin = reinterpret_cast<const char *>(first);
462 const char *s_end = reinterpret_cast<const char *>(last);
463 const size_t length = std::distance(first: s_begin, last: s_end);
464 if (length <= 64)
465 return hash_short(s: s_begin, length, seed);
466
467 const char *s_aligned_end = s_begin + (length & ~63);
468 hash_state state = state.create(s: s_begin, seed);
469 s_begin += 64;
470 while (s_begin != s_aligned_end) {
471 state.mix(s: s_begin);
472 s_begin += 64;
473 }
474 if (length & 63)
475 state.mix(s: s_end - 64);
476
477 return state.finalize(length);
478}
479
480} // namespace detail
481} // namespace hashing
482
483
484/// Compute a hash_code for a sequence of values.
485///
486/// This hashes a sequence of values. It produces the same hash_code as
487/// 'hash_combine(a, b, c, ...)', but can run over arbitrary sized sequences
488/// and is significantly faster given pointers and types which can be hashed as
489/// a sequence of bytes.
490template <typename InputIteratorT>
491hash_code hash_combine_range(InputIteratorT first, InputIteratorT last) {
492 return ::llvm::hashing::detail::hash_combine_range_impl(first, last);
493}
494
495
496// Implementation details for hash_combine.
497namespace hashing {
498namespace detail {
499
500/// Helper class to manage the recursive combining of hash_combine
501/// arguments.
502///
503/// This class exists to manage the state and various calls involved in the
504/// recursive combining of arguments used in hash_combine. It is particularly
505/// useful at minimizing the code in the recursive calls to ease the pain
506/// caused by a lack of variadic functions.
507struct hash_combine_recursive_helper {
508 char buffer[64] = {};
509 hash_state state;
510 const uint64_t seed;
511
512public:
513 /// Construct a recursive hash combining helper.
514 ///
515 /// This sets up the state for a recursive hash combine, including getting
516 /// the seed and buffer setup.
517 hash_combine_recursive_helper()
518 : seed(get_execution_seed()) {}
519
520 /// Combine one chunk of data into the current in-flight hash.
521 ///
522 /// This merges one chunk of data into the hash. First it tries to buffer
523 /// the data. If the buffer is full, it hashes the buffer into its
524 /// hash_state, empties it, and then merges the new chunk in. This also
525 /// handles cases where the data straddles the end of the buffer.
526 template <typename T>
527 char *combine_data(size_t &length, char *buffer_ptr, char *buffer_end, T data) {
528 if (!store_and_advance(buffer_ptr, buffer_end, data)) {
529 // Check for skew which prevents the buffer from being packed, and do
530 // a partial store into the buffer to fill it. This is only a concern
531 // with the variadic combine because that formation can have varying
532 // argument types.
533 size_t partial_store_size = buffer_end - buffer_ptr;
534 memcpy(buffer_ptr, &data, partial_store_size);
535
536 // If the store fails, our buffer is full and ready to hash. We have to
537 // either initialize the hash state (on the first full buffer) or mix
538 // this buffer into the existing hash state. Length tracks the *hashed*
539 // length, not the buffered length.
540 if (length == 0) {
541 state = state.create(s: buffer, seed);
542 length = 64;
543 } else {
544 // Mix this chunk into the current state and bump length up by 64.
545 state.mix(s: buffer);
546 length += 64;
547 }
548 // Reset the buffer_ptr to the head of the buffer for the next chunk of
549 // data.
550 buffer_ptr = buffer;
551
552 // Try again to store into the buffer -- this cannot fail as we only
553 // store types smaller than the buffer.
554 if (!store_and_advance(buffer_ptr, buffer_end, data,
555 partial_store_size))
556 llvm_unreachable("buffer smaller than stored type");
557 }
558 return buffer_ptr;
559 }
560
561 /// Recursive, variadic combining method.
562 ///
563 /// This function recurses through each argument, combining that argument
564 /// into a single hash.
565 template <typename T, typename ...Ts>
566 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
567 const T &arg, const Ts &...args) {
568 buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg));
569
570 // Recurse to the next argument.
571 return combine(length, buffer_ptr, buffer_end, args...);
572 }
573
574 /// Base case for recursive, variadic combining.
575 ///
576 /// The base case when combining arguments recursively is reached when all
577 /// arguments have been handled. It flushes the remaining buffer and
578 /// constructs a hash_code.
579 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end) {
580 // Check whether the entire set of values fit in the buffer. If so, we'll
581 // use the optimized short hashing routine and skip state entirely.
582 if (length == 0)
583 return hash_short(s: buffer, length: buffer_ptr - buffer, seed);
584
585 // Mix the final buffer, rotating it if we did a partial fill in order to
586 // simulate doing a mix of the last 64-bytes. That is how the algorithm
587 // works when we have a contiguous byte sequence, and we want to emulate
588 // that here.
589 std::rotate(first: buffer, middle: buffer_ptr, last: buffer_end);
590
591 // Mix this chunk into the current state.
592 state.mix(s: buffer);
593 length += buffer_ptr - buffer;
594
595 return state.finalize(length);
596 }
597};
598
599} // namespace detail
600} // namespace hashing
601
602/// Combine values into a single hash_code.
603///
604/// This routine accepts a varying number of arguments of any type. It will
605/// attempt to combine them into a single hash_code. For user-defined types it
606/// attempts to call a \see hash_value overload (via ADL) for the type. For
607/// integer and pointer types it directly combines their data into the
608/// resulting hash_code.
609///
610/// The result is suitable for returning from a user's hash_value
611/// *implementation* for their user-defined type. Consumers of a type should
612/// *not* call this routine, they should instead call 'hash_value'.
613template <typename ...Ts> hash_code hash_combine(const Ts &...args) {
614 // Recursively hash each argument using a helper class.
615 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
616 return helper.combine(0, helper.buffer, helper.buffer + 64, args...);
617}
618
619// Implementation details for implementations of hash_value overloads provided
620// here.
621namespace hashing {
622namespace detail {
623
624/// Helper to hash the value of a single integer.
625///
626/// Overloads for smaller integer types are not provided to ensure consistent
627/// behavior in the presence of integral promotions. Essentially,
628/// "hash_value('4')" and "hash_value('0' + 4)" should be the same.
629inline hash_code hash_integer_value(uint64_t value) {
630 // Similar to hash_4to8_bytes but using a seed instead of length.
631 const uint64_t seed = get_execution_seed();
632 const char *s = reinterpret_cast<const char *>(&value);
633 const uint64_t a = fetch32(p: s);
634 return hash_16_bytes(low: seed + (a << 3), high: fetch32(p: s + 4));
635}
636
637} // namespace detail
638} // namespace hashing
639
640// Declared and documented above, but defined here so that any of the hashing
641// infrastructure is available.
642template <typename T>
643std::enable_if_t<is_integral_or_enum<T>::value, hash_code> hash_value(T value) {
644 return ::llvm::hashing::detail::hash_integer_value(
645 value: static_cast<uint64_t>(value));
646}
647
648// Declared and documented above, but defined here so that any of the hashing
649// infrastructure is available.
650template <typename T> hash_code hash_value(const T *ptr) {
651 return ::llvm::hashing::detail::hash_integer_value(
652 value: reinterpret_cast<uintptr_t>(ptr));
653}
654
655// Declared and documented above, but defined here so that any of the hashing
656// infrastructure is available.
657template <typename T, typename U>
658hash_code hash_value(const std::pair<T, U> &arg) {
659 return hash_combine(arg.first, arg.second);
660}
661
662template <typename... Ts> hash_code hash_value(const std::tuple<Ts...> &arg) {
663 return std::apply([](const auto &...xs) { return hash_combine(xs...); }, arg);
664}
665
666// Declared and documented above, but defined here so that any of the hashing
667// infrastructure is available.
668template <typename T>
669hash_code hash_value(const std::basic_string<T> &arg) {
670 return hash_combine_range(arg.begin(), arg.end());
671}
672
673template <typename T> hash_code hash_value(const std::optional<T> &arg) {
674 return arg ? hash_combine(true, *arg) : hash_value(value: false);
675}
676
677template <> struct DenseMapInfo<hash_code, void> {
678 static inline hash_code getEmptyKey() { return hash_code(-1); }
679 static inline hash_code getTombstoneKey() { return hash_code(-2); }
680 static unsigned getHashValue(hash_code val) { return val; }
681 static bool isEqual(hash_code LHS, hash_code RHS) { return LHS == RHS; }
682};
683
684} // namespace llvm
685
686#endif
687

source code of include/llvm-17/llvm/ADT/Hashing.h