1 //===-- llvm/ADT/Hashing.h - Utilities for hashing --------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the newly proposed standard C++ interfaces for hashing
11 // arbitrary data and building hash functions for user-defined types. This
12 // interface was originally proposed in N3333[1] and is currently under review
13 // for inclusion in a future TR and/or standard.
15 // The primary interfaces provide are comprised of one type and three functions:
17 // -- 'hash_code' class is an opaque type representing the hash code for some
18 // data. It is the intended product of hashing, and can be used to implement
19 // hash tables, checksumming, and other common uses of hashes. It is not an
20 // integer type (although it can be converted to one) because it is risky
21 // to assume much about the internals of a hash_code. In particular, each
22 // execution of the program has a high probability of producing a different
23 // hash_code for a given input. Thus their values are not stable to save or
24 // persist, and should only be used during the execution for the
25 // construction of hashing datastructures.
27 // -- 'hash_value' is a function designed to be overloaded for each
28 // user-defined type which wishes to be used within a hashing context. It
29 // should be overloaded within the user-defined type's namespace and found
30 // via ADL. Overloads for primitive types are provided by this library.
32 // -- 'hash_combine' and 'hash_combine_range' are functions designed to aid
33 // programmers in easily and intuitively combining a set of data into
34 // a single hash_code for their object. They should only logically be used
35 // within the implementation of a 'hash_value' routine or similar context.
37 // Note that 'hash_combine_range' contains very special logic for hashing
38 // a contiguous array of integers or pointers. This logic is *extremely* fast,
39 // on a modern Intel "Gainestown" Xeon (Nehalem uarch) @2.2 GHz, these were
40 // benchmarked at over 6.5 GiB/s for large keys, and <20 cycles/hash for keys
43 //===----------------------------------------------------------------------===//
45 #ifndef LLVM_ADT_HASHING_H
46 #define LLVM_ADT_HASHING_H
48 #include "llvm/ADT/STLExtras.h"
49 #include "llvm/Support/DataTypes.h"
50 #include "llvm/Support/Host.h"
51 #include "llvm/Support/SwapByteOrder.h"
52 #include "llvm/Support/type_traits.h"
59 // Allow detecting C++11 feature availability when building with Clang without
60 // breaking other compilers.
62 # define __has_feature(x) 0
67 /// \brief An opaque object representing a hash code.
69 /// This object represents the result of hashing some entity. It is intended to
70 /// be used to implement hashtables or other hashing-based data structures.
71 /// While it wraps and exposes a numeric value, this value should not be
72 /// trusted to be stable or predictable across processes or executions.
74 /// In order to obtain the hash_code for an object 'x':
76 /// using llvm::hash_value;
77 /// llvm::hash_code code = hash_value(x);
80 /// Also note that there are two numerical values which are reserved, and the
81 /// implementation ensures will never be produced for real hash_codes. These
82 /// can be used as sentinels within hashing data structures.
87 /// \brief Default construct a hash_code.
88 /// Note that this leaves the value uninitialized.
91 /// \brief Form a hash code directly from a numerical value.
92 hash_code(size_t value) : value(value) {}
94 /// \brief Convert the hash code to its numerical value for use.
95 /*explicit*/ operator size_t() const { return value; }
97 friend bool operator==(const hash_code &lhs, const hash_code &rhs) {
98 return lhs.value == rhs.value;
100 friend bool operator!=(const hash_code &lhs, const hash_code &rhs) {
101 return lhs.value != rhs.value;
104 /// \brief Allow a hash_code to be directly run through hash_value.
105 friend size_t hash_value(const hash_code &code) { return code.value; }
108 /// \brief Compute a hash_code for any integer value.
110 /// Note that this function is intended to compute the same hash_code for
111 /// a particular value without regard to the pre-promotion type. This is in
112 /// contrast to hash_combine which may produce different hash_codes for
113 /// differing argument types even if they would implicit promote to a common
114 /// type without changing the value.
115 template <typename T>
116 typename enable_if<is_integral<T>, hash_code>::type hash_value(T value);
118 /// \brief Compute a hash_code for a pointer's address.
120 /// N.B.: This hashes the *address*. Not the value and not the type.
121 template <typename T> hash_code hash_value(const T *ptr);
123 /// \brief Compute a hash_code for a pair of objects.
124 template <typename T, typename U>
125 hash_code hash_value(const std::pair<T, U> &arg);
127 /// \brief Compute a hash_code for a standard string.
128 template <typename T>
129 hash_code hash_value(const std::basic_string<T> &arg);
132 /// \brief Override the execution seed with a fixed value.
134 /// This hashing library uses a per-execution seed designed to change on each
135 /// run with high probability in order to ensure that the hash codes are not
136 /// attackable and to ensure that output which is intended to be stable does
137 /// not rely on the particulars of the hash codes produced.
139 /// That said, there are use cases where it is important to be able to
140 /// reproduce *exactly* a specific behavior. To that end, we provide a function
141 /// which will forcibly set the seed to a fixed value. This must be done at the
142 /// start of the program, before any hashes are computed. Also, it cannot be
143 /// undone. This makes it thread-hostile and very hard to use outside of
144 /// immediately on start of a simple program designed for reproducible
146 void set_fixed_execution_hash_seed(size_t fixed_value);
149 // All of the implementation details of actually computing the various hash
150 // code values are held within this namespace. These routines are included in
151 // the header file mainly to allow inlining and constant propagation.
155 inline uint64_t fetch64(const char *p) {
157 memcpy(&result, p, sizeof(result));
158 if (sys::isBigEndianHost())
159 return sys::SwapByteOrder(result);
163 inline uint32_t fetch32(const char *p) {
165 memcpy(&result, p, sizeof(result));
166 if (sys::isBigEndianHost())
167 return sys::SwapByteOrder(result);
171 /// Some primes between 2^63 and 2^64 for various uses.
172 static const uint64_t k0 = 0xc3a5c85c97cb3127ULL;
173 static const uint64_t k1 = 0xb492b66fbe98f273ULL;
174 static const uint64_t k2 = 0x9ae16a3b2f90404fULL;
175 static const uint64_t k3 = 0xc949d7c7509e6557ULL;
177 /// \brief Bitwise right rotate.
178 /// Normally this will compile to a single instruction, especially if the
179 /// shift is a manifest constant.
180 inline uint64_t rotate(uint64_t val, size_t shift) {
181 // Avoid shifting by 64: doing so yields an undefined result.
182 return shift == 0 ? val : ((val >> shift) | (val << (64 - shift)));
185 inline uint64_t shift_mix(uint64_t val) {
186 return val ^ (val >> 47);
189 inline uint64_t hash_16_bytes(uint64_t low, uint64_t high) {
190 // Murmur-inspired hashing.
191 const uint64_t kMul = 0x9ddfea08eb382d69ULL;
192 uint64_t a = (low ^ high) * kMul;
194 uint64_t b = (high ^ a) * kMul;
200 inline uint64_t hash_1to3_bytes(const char *s, size_t len, uint64_t seed) {
202 uint8_t b = s[len >> 1];
203 uint8_t c = s[len - 1];
204 uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);
205 uint32_t z = len + (static_cast<uint32_t>(c) << 2);
206 return shift_mix(y * k2 ^ z * k3 ^ seed) * k2;
209 inline uint64_t hash_4to8_bytes(const char *s, size_t len, uint64_t seed) {
210 uint64_t a = fetch32(s);
211 return hash_16_bytes(len + (a << 3), seed ^ fetch32(s + len - 4));
214 inline uint64_t hash_9to16_bytes(const char *s, size_t len, uint64_t seed) {
215 uint64_t a = fetch64(s);
216 uint64_t b = fetch64(s + len - 8);
217 return hash_16_bytes(seed ^ a, rotate(b + len, len)) ^ b;
220 inline uint64_t hash_17to32_bytes(const char *s, size_t len, uint64_t seed) {
221 uint64_t a = fetch64(s) * k1;
222 uint64_t b = fetch64(s + 8);
223 uint64_t c = fetch64(s + len - 8) * k2;
224 uint64_t d = fetch64(s + len - 16) * k0;
225 return hash_16_bytes(rotate(a - b, 43) + rotate(c ^ seed, 30) + d,
226 a + rotate(b ^ k3, 20) - c + len + seed);
229 inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) {
230 uint64_t z = fetch64(s + 24);
231 uint64_t a = fetch64(s) + (len + fetch64(s + len - 16)) * k0;
232 uint64_t b = rotate(a + z, 52);
233 uint64_t c = rotate(a, 37);
236 a += fetch64(s + 16);
238 uint64_t vs = b + rotate(a, 31) + c;
239 a = fetch64(s + 16) + fetch64(s + len - 32);
240 z = fetch64(s + len - 8);
241 b = rotate(a + z, 52);
243 a += fetch64(s + len - 24);
245 a += fetch64(s + len - 16);
247 uint64_t ws = b + rotate(a, 31) + c;
248 uint64_t r = shift_mix((vf + ws) * k2 + (wf + vs) * k0);
249 return shift_mix((seed ^ (r * k0)) + vs) * k2;
252 inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) {
253 if (length >= 4 && length <= 8)
254 return hash_4to8_bytes(s, length, seed);
255 if (length > 8 && length <= 16)
256 return hash_9to16_bytes(s, length, seed);
257 if (length > 16 && length <= 32)
258 return hash_17to32_bytes(s, length, seed);
260 return hash_33to64_bytes(s, length, seed);
262 return hash_1to3_bytes(s, length, seed);
267 /// \brief The intermediate state used during hashing.
268 /// Currently, the algorithm for computing hash codes is based on CityHash and
269 /// keeps 56 bytes of arbitrary state.
271 uint64_t h0, h1, h2, h3, h4, h5, h6;
274 /// \brief Create a new hash_state structure and initialize it based on the
275 /// seed and the first 64-byte chunk.
276 /// This effectively performs the initial mix.
277 static hash_state create(const char *s, uint64_t seed) {
279 0, seed, hash_16_bytes(seed, k1), rotate(seed ^ k1, 49),
280 seed * k1, shift_mix(seed), 0, seed };
281 state.h6 = hash_16_bytes(state.h4, state.h5);
286 /// \brief Mix 32-bytes from the input sequence into the 16-bytes of 'a'
287 /// and 'b', including whatever is already in 'a' and 'b'.
288 static void mix_32_bytes(const char *s, uint64_t &a, uint64_t &b) {
290 uint64_t c = fetch64(s + 24);
291 b = rotate(b + a + c, 21);
293 a += fetch64(s + 8) + fetch64(s + 16);
294 b += rotate(a, 44) + d;
298 /// \brief Mix in a 64-byte buffer of data.
299 /// We mix all 64 bytes even when the chunk length is smaller, but we
300 /// record the actual length.
301 void mix(const char *s) {
302 h0 = rotate(h0 + h1 + h3 + fetch64(s + 8), 37) * k1;
303 h1 = rotate(h1 + h4 + fetch64(s + 48), 42) * k1;
305 h1 += h3 + fetch64(s + 40);
306 h2 = rotate(h2 + h5, 33) * k1;
309 mix_32_bytes(s, h3, h4);
311 h6 = h1 + fetch64(s + 16);
312 mix_32_bytes(s + 32, h5, h6);
316 /// \brief Compute the final 64-bit hash code value based on the current
317 /// state and the length of bytes hashed.
318 uint64_t finalize(size_t length) {
319 return hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2,
320 hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0);
325 /// \brief A global, fixed seed-override variable.
327 /// This variable can be set using the \see llvm::set_fixed_execution_seed
328 /// function. See that function for details. Do not, under any circumstances,
329 /// set or read this variable.
330 extern size_t fixed_seed_override;
332 inline size_t get_execution_seed() {
333 // FIXME: This needs to be a per-execution seed. This is just a placeholder
334 // implementation. Switching to a per-execution seed is likely to flush out
335 // instability bugs and so will happen as its own commit.
337 // However, if there is a fixed seed override set the first time this is
338 // called, return that instead of the per-execution seed.
339 const uint64_t seed_prime = 0xff51afd7ed558ccdULL;
340 static size_t seed = fixed_seed_override ? fixed_seed_override
341 : static_cast<size_t>(seed_prime);
346 /// \brief Trait to indicate whether a type's bits can be hashed directly.
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.
352 // FIXME: We want to replace is_integral and is_pointer here with a predicate
353 // which asserts that comparing the underlying storage of two values of the
354 // type for equality is equivalent to comparing the two values for equality.
355 // For all the platforms we care about, this holds for integers and pointers,
356 // but there are platforms where it doesn't and we would like to support
357 // user-defined types which happen to satisfy this property.
358 template <typename T> struct is_hashable_data
359 : integral_constant<bool, ((is_integral<T>::value || is_pointer<T>::value) &&
360 64 % sizeof(T) == 0)> {};
362 // Special case std::pair to detect when both types are viable and when there
363 // is no alignment-derived padding in the pair. This is a bit of a lie because
364 // std::pair isn't truly POD, but it's close enough in all reasonable
365 // implementations for our use case of hashing the underlying data.
366 template <typename T, typename U> struct is_hashable_data<std::pair<T, U> >
367 : integral_constant<bool, (is_hashable_data<T>::value &&
368 is_hashable_data<U>::value &&
369 (sizeof(T) + sizeof(U)) ==
370 sizeof(std::pair<T, U>))> {};
372 /// \brief Helper to get the hashable data representation for a type.
373 /// This variant is enabled when the type itself can be used.
374 template <typename T>
375 typename enable_if<is_hashable_data<T>, T>::type
376 get_hashable_data(const T &value) {
379 /// \brief Helper to get the hashable data representation for a type.
380 /// This variant is enabled when we must first call hash_value and use the
381 /// result as our data.
382 template <typename T>
383 typename enable_if_c<!is_hashable_data<T>::value, size_t>::type
384 get_hashable_data(const T &value) {
385 using ::llvm::hash_value;
386 return hash_value(value);
389 /// \brief Helper to store data from a value into a buffer and advance the
390 /// pointer into that buffer.
392 /// This routine first checks whether there is enough space in the provided
393 /// buffer, and if not immediately returns false. If there is space, it
394 /// copies the underlying bytes of value into the buffer, advances the
395 /// buffer_ptr past the copied bytes, and returns true.
396 template <typename T>
397 bool store_and_advance(char *&buffer_ptr, char *buffer_end, const T& value,
399 size_t store_size = sizeof(value) - offset;
400 if (buffer_ptr + store_size > buffer_end)
402 const char *value_data = reinterpret_cast<const char *>(&value);
403 memcpy(buffer_ptr, value_data + offset, store_size);
404 buffer_ptr += store_size;
408 /// \brief Implement the combining of integral values into a hash_code.
410 /// This overload is selected when the value type of the iterator is
411 /// integral. Rather than computing a hash_code for each object and then
412 /// combining them, this (as an optimization) directly combines the integers.
413 template <typename InputIteratorT>
414 hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) {
415 typedef typename std::iterator_traits<InputIteratorT>::value_type ValueT;
416 const size_t seed = get_execution_seed();
417 char buffer[64], *buffer_ptr = buffer;
418 char *const buffer_end = buffer_ptr + array_lengthof(buffer);
419 while (first != last && store_and_advance(buffer_ptr, buffer_end,
420 get_hashable_data(*first)))
422 /// \brief Metafunction that determines whether the given type is an integral
425 return hash_short(buffer, buffer_ptr - buffer, seed);
426 assert(buffer_ptr == buffer_end);
428 hash_state state = state.create(buffer, seed);
430 while (first != last) {
431 // Fill up the buffer. We don't clear it, which re-mixes the last round
432 // when only a partial 64-byte chunk is left.
434 while (first != last && store_and_advance(buffer_ptr, buffer_end,
435 get_hashable_data(*first)))
438 // Rotate the buffer if we did a partial fill in order to simulate doing
439 // a mix of the last 64-bytes. That is how the algorithm works when we
440 // have a contiguous byte sequence, and we want to emulate that here.
441 std::rotate(buffer, buffer_ptr, buffer_end);
443 // Mix this chunk into the current state.
445 length += buffer_ptr - buffer;
448 return state.finalize(length);
451 /// \brief Implement the combining of integral values into a hash_code.
453 /// This overload is selected when the value type of the iterator is integral
454 /// and when the input iterator is actually a pointer. Rather than computing
455 /// a hash_code for each object and then combining them, this (as an
456 /// optimization) directly combines the integers. Also, because the integers
457 /// are stored in contiguous memory, this routine avoids copying each value
458 /// and directly reads from the underlying memory.
459 template <typename ValueT>
460 typename enable_if<is_hashable_data<ValueT>, hash_code>::type
461 hash_combine_range_impl(const ValueT *first, const ValueT *last) {
462 const size_t seed = get_execution_seed();
463 const char *s_begin = reinterpret_cast<const char *>(first);
464 const char *s_end = reinterpret_cast<const char *>(last);
465 const size_t length = std::distance(s_begin, s_end);
467 return hash_short(s_begin, length, seed);
469 const char *s_aligned_end = s_begin + (length & ~63);
470 hash_state state = state.create(s_begin, seed);
472 while (s_begin != s_aligned_end) {
477 state.mix(s_end - 64);
479 return state.finalize(length);
482 } // namespace detail
483 } // namespace hashing
486 /// \brief Compute a hash_code for a sequence of values.
488 /// This hashes a sequence of values. It produces the same hash_code as
489 /// 'hash_combine(a, b, c, ...)', but can run over arbitrary sized sequences
490 /// and is significantly faster given pointers and types which can be hashed as
491 /// a sequence of bytes.
492 template <typename InputIteratorT>
493 hash_code hash_combine_range(InputIteratorT first, InputIteratorT last) {
494 return ::llvm::hashing::detail::hash_combine_range_impl(first, last);
498 // Implementation details for hash_combine.
502 /// \brief Helper class to manage the recursive combining of hash_combine
505 /// This class exists to manage the state and various calls involved in the
506 /// recursive combining of arguments used in hash_combine. It is particularly
507 /// useful at minimizing the code in the recursive calls to ease the pain
508 /// caused by a lack of variadic functions.
509 class hash_combine_recursive_helper {
512 char *const buffer_end;
518 /// \brief Construct a recursive hash combining helper.
520 /// This sets up the state for a recursive hash combine, including getting
521 /// the seed and buffer setup.
522 hash_combine_recursive_helper()
523 : seed(get_execution_seed()),
524 buffer_end(buffer + array_lengthof(buffer)),
528 /// \brief Combine one chunk of data into the current in-flight hash.
530 /// This merges one chunk of data into the hash. First it tries to buffer
531 /// the data. If the buffer is full, it hashes the buffer into its
532 /// hash_state, empties it, and then merges the new chunk in. This also
533 /// handles cases where the data straddles the end of the buffer.
534 template <typename T> void combine_data(T data) {
535 if (!store_and_advance(buffer_ptr, buffer_end, data)) {
536 // Check for skew which prevents the buffer from being packed, and do
537 // a partial store into the buffer to fill it. This is only a concern
538 // with the variadic combine because that formation can have varying
540 size_t partial_store_size = buffer_end - buffer_ptr;
541 memcpy(buffer_ptr, &data, partial_store_size);
543 // If the store fails, our buffer is full and ready to hash. We have to
544 // either initialize the hash state (on the first full buffer) or mix
545 // this buffer into the existing hash state. Length tracks the *hashed*
546 // length, not the buffered length.
548 state = state.create(buffer, seed);
551 // Mix this chunk into the current state and bump length up by 64.
555 // Reset the buffer_ptr to the head of the buffer for the next chunk of
559 // Try again to store into the buffer -- this cannot fail as we only
560 // store types smaller than the buffer.
561 if (!store_and_advance(buffer_ptr, buffer_end, data,
567 #if defined(__has_feature) && __has_feature(__cxx_variadic_templates__)
569 /// \brief Recursive, variadic combining method.
571 /// This function recurses through each argument, combining that argument
572 /// into a single hash.
573 template <typename T, typename ...Ts>
574 hash_code combine(const T &arg, const Ts &...args) {
575 combine_data( get_hashable_data(arg));
577 // Recurse to the next argument.
578 return combine(args...);
582 // Manually expanded recursive combining methods. See variadic above for
585 template <typename T1, typename T2, typename T3, typename T4, typename T5,
587 hash_code combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
588 const T4 &arg4, const T5 &arg5, const T6 &arg6) {
589 combine_data(get_hashable_data(arg1));
590 return combine(arg2, arg3, arg4, arg5, arg6);
592 template <typename T1, typename T2, typename T3, typename T4, typename T5>
593 hash_code combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
594 const T4 &arg4, const T5 &arg5) {
595 combine_data(get_hashable_data(arg1));
596 return combine(arg2, arg3, arg4, arg5);
598 template <typename T1, typename T2, typename T3, typename T4>
599 hash_code combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
601 combine_data(get_hashable_data(arg1));
602 return combine(arg2, arg3, arg4);
604 template <typename T1, typename T2, typename T3>
605 hash_code combine(const T1 &arg1, const T2 &arg2, const T3 &arg3) {
606 combine_data(get_hashable_data(arg1));
607 return combine(arg2, arg3);
609 template <typename T1, typename T2>
610 hash_code combine(const T1 &arg1, const T2 &arg2) {
611 combine_data(get_hashable_data(arg1));
612 return combine(arg2);
614 template <typename T1>
615 hash_code combine(const T1 &arg1) {
616 combine_data(get_hashable_data(arg1));
622 /// \brief Base case for recursive, variadic combining.
624 /// The base case when combining arguments recursively is reached when all
625 /// arguments have been handled. It flushes the remaining buffer and
626 /// constructs a hash_code.
627 hash_code combine() {
628 // Check whether the entire set of values fit in the buffer. If so, we'll
629 // use the optimized short hashing routine and skip state entirely.
631 return hash_short(buffer, buffer_ptr - buffer, seed);
633 // Mix the final buffer, rotating it if we did a partial fill in order to
634 // simulate doing a mix of the last 64-bytes. That is how the algorithm
635 // works when we have a contiguous byte sequence, and we want to emulate
637 std::rotate(buffer, buffer_ptr, buffer_end);
639 // Mix this chunk into the current state.
641 length += buffer_ptr - buffer;
643 return state.finalize(length);
647 } // namespace detail
648 } // namespace hashing
651 #if __has_feature(__cxx_variadic_templates__)
653 /// \brief Combine values into a single hash_code.
655 /// This routine accepts a varying number of arguments of any type. It will
656 /// attempt to combine them into a single hash_code. For user-defined types it
657 /// attempts to call a \see hash_value overload (via ADL) for the type. For
658 /// integer and pointer types it directly combines their data into the
659 /// resulting hash_code.
661 /// The result is suitable for returning from a user's hash_value
662 /// *implementation* for their user-defined type. Consumers of a type should
663 /// *not* call this routine, they should instead call 'hash_value'.
664 template <typename ...Ts> hash_code hash_combine(const Ts &...args) {
665 // Recursively hash each argument using a helper class.
666 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
667 return helper.combine(args...);
672 // What follows are manually exploded overloads for each argument width. See
673 // the above variadic definition for documentation and specification.
675 template <typename T1, typename T2, typename T3, typename T4, typename T5,
677 hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
678 const T4 &arg4, const T5 &arg5, const T6 &arg6) {
679 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
680 return helper.combine(arg1, arg2, arg3, arg4, arg5, arg6);
682 template <typename T1, typename T2, typename T3, typename T4, typename T5>
683 hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
684 const T4 &arg4, const T5 &arg5) {
685 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
686 return helper.combine(arg1, arg2, arg3, arg4, arg5);
688 template <typename T1, typename T2, typename T3, typename T4>
689 hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
691 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
692 return helper.combine(arg1, arg2, arg3, arg4);
694 template <typename T1, typename T2, typename T3>
695 hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3) {
696 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
697 return helper.combine(arg1, arg2, arg3);
699 template <typename T1, typename T2>
700 hash_code hash_combine(const T1 &arg1, const T2 &arg2) {
701 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
702 return helper.combine(arg1, arg2);
704 template <typename T1>
705 hash_code hash_combine(const T1 &arg1) {
706 ::llvm::hashing::detail::hash_combine_recursive_helper helper;
707 return helper.combine(arg1);
713 // Implementation details for implementatinos of hash_value overloads provided
718 /// \brief Helper to hash the value of a single integer.
720 /// Overloads for smaller integer types are not provided to ensure consistent
721 /// behavior in the presence of integral promotions. Essentially,
722 /// "hash_value('4')" and "hash_value('0' + 4)" should be the same.
723 inline hash_code hash_integer_value(uint64_t value) {
724 // Similar to hash_4to8_bytes but using a seed instead of length.
725 const uint64_t seed = get_execution_seed();
726 const char *s = reinterpret_cast<const char *>(&value);
727 const uint64_t a = fetch32(s);
728 return hash_16_bytes(seed + (a << 3), fetch32(s + 4));
731 } // namespace detail
732 } // namespace hashing
734 // Declared and documented above, but defined here so that any of the hashing
735 // infrastructure is available.
736 template <typename T>
737 typename enable_if<is_integral<T>, hash_code>::type hash_value(T value) {
738 return ::llvm::hashing::detail::hash_integer_value(value);
741 // Declared and documented above, but defined here so that any of the hashing
742 // infrastructure is available.
743 template <typename T> hash_code hash_value(const T *ptr) {
744 return ::llvm::hashing::detail::hash_integer_value(
745 reinterpret_cast<uintptr_t>(ptr));
748 // Declared and documented above, but defined here so that any of the hashing
749 // infrastructure is available.
750 template <typename T, typename U>
751 hash_code hash_value(const std::pair<T, U> &arg) {
752 return hash_combine(arg.first, arg.second);
755 // Declared and documented above, but defined here so that any of the hashing
756 // infrastructure is available.
757 template <typename T>
758 hash_code hash_value(const std::basic_string<T> &arg) {
759 return hash_combine_range(arg.begin(), arg.end());