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 58 namespace 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 72 class hash_code { 73 size_t value; 74 75 public: 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. 104 template <typename T> 105 std::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. 110 template <typename T> hash_code hash_value(const T *ptr); 111 112 /// Compute a hash_code for a pair of objects. 113 template <typename T, typename U> 114 hash_code hash_value(const std::pair<T, U> &arg); 115 116 /// Compute a hash_code for a tuple. 117 template <typename... Ts> 118 hash_code hash_value(const std::tuple<Ts...> &arg); 119 120 /// Compute a hash_code for a standard string. 121 template <typename T> 122 hash_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. 139 void 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. 145 namespace hashing { 146 namespace detail { 147 148 inline 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 } 155 156 inline 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. 165 static constexpr uint64_t k0 = 0xc3a5c85c97cb3127ULL; 166 static constexpr uint64_t k1 = 0xb492b66fbe98f273ULL; 167 static constexpr uint64_t k2 = 0x9ae16a3b2f90404fULL; 168 static 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. 173 inline 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 } 177 178 inline uint64_t shift_mix(uint64_t val) { 179 return val ^ (val >> 47); 180 } 181 182 inline 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 } 192 193 inline 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 } 201 202 inline 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 } 206 207 inline 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 } 212 213 inline 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 } 221 222 inline 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 } 244 245 inline 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. 263 struct 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. 322 extern uint64_t fixed_seed_override; 323 324 inline 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. 349 template <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. 358 template <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. 366 template <typename T> 367 std::enable_if_t<is_hashable_data<T>::value, T> 368 get_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. 374 template <typename T> 375 std::enable_if_t<!is_hashable_data<T>::value, size_t> 376 get_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. 388 template <typename T> 389 bool 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. 405 template <typename InputIteratorT> 406 hash_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. 448 template <typename ValueT> 449 std::enable_if_t<is_hashable_data<ValueT>::value, hash_code> 450 hash_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. 481 template <typename InputIteratorT> 482 hash_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. 488 namespace hashing { 489 namespace 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. 498 struct hash_combine_recursive_helper { 499 char buffer[64] = {}; 500 hash_state state; 501 const uint64_t seed; 502 503 public: 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'. 604 template <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. 612 namespace hashing { 613 namespace 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. 620 inline 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. 633 template <typename T> 634 std::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. 641 template <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. 648 template <typename T, typename U> 649 hash_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<...>(...). 654 namespace hashing { 655 namespace detail { 656 657 template <typename... Ts, std::size_t... Indices> 658 hash_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 665 666 template <typename... Ts> 667 hash_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. 675 template <typename T> 676 hash_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