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