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