Hashing.h revision 360784
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 <utility> 56 57namespace llvm { 58 59/// An opaque object representing a hash code. 60/// 61/// This object represents the result of hashing some entity. It is intended to 62/// be used to implement hashtables or other hashing-based data structures. 63/// While it wraps and exposes a numeric value, this value should not be 64/// trusted to be stable or predictable across processes or executions. 65/// 66/// In order to obtain the hash_code for an object 'x': 67/// \code 68/// using llvm::hash_value; 69/// llvm::hash_code code = hash_value(x); 70/// \endcode 71class hash_code { 72 size_t value; 73 74public: 75 /// Default construct a hash_code. 76 /// Note that this leaves the value uninitialized. 77 hash_code() = default; 78 79 /// Form a hash code directly from a numerical value. 80 hash_code(size_t value) : value(value) {} 81 82 /// Convert the hash code to its numerical value for use. 83 /*explicit*/ operator size_t() const { return value; } 84 85 friend bool operator==(const hash_code &lhs, const hash_code &rhs) { 86 return lhs.value == rhs.value; 87 } 88 friend bool operator!=(const hash_code &lhs, const hash_code &rhs) { 89 return lhs.value != rhs.value; 90 } 91 92 /// Allow a hash_code to be directly run through hash_value. 93 friend size_t hash_value(const hash_code &code) { return code.value; } 94}; 95 96/// Compute a hash_code for any integer value. 97/// 98/// Note that this function is intended to compute the same hash_code for 99/// a particular value without regard to the pre-promotion type. This is in 100/// contrast to hash_combine which may produce different hash_codes for 101/// differing argument types even if they would implicit promote to a common 102/// type without changing the value. 103template <typename T> 104typename std::enable_if<is_integral_or_enum<T>::value, hash_code>::type 105hash_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 standard string. 117template <typename T> 118hash_code hash_value(const std::basic_string<T> &arg); 119 120 121/// Override the execution seed with a fixed value. 122/// 123/// This hashing library uses a per-execution seed designed to change on each 124/// run with high probability in order to ensure that the hash codes are not 125/// attackable and to ensure that output which is intended to be stable does 126/// not rely on the particulars of the hash codes produced. 127/// 128/// That said, there are use cases where it is important to be able to 129/// reproduce *exactly* a specific behavior. To that end, we provide a function 130/// which will forcibly set the seed to a fixed value. This must be done at the 131/// start of the program, before any hashes are computed. Also, it cannot be 132/// undone. This makes it thread-hostile and very hard to use outside of 133/// immediately on start of a simple program designed for reproducible 134/// behavior. 135void set_fixed_execution_hash_seed(uint64_t fixed_value); 136 137 138// All of the implementation details of actually computing the various hash 139// code values are held within this namespace. These routines are included in 140// the header file mainly to allow inlining and constant propagation. 141namespace hashing { 142namespace detail { 143 144inline uint64_t fetch64(const char *p) { 145 uint64_t result; 146 memcpy(&result, p, sizeof(result)); 147 if (sys::IsBigEndianHost) 148 sys::swapByteOrder(result); 149 return result; 150} 151 152inline uint32_t fetch32(const char *p) { 153 uint32_t result; 154 memcpy(&result, p, sizeof(result)); 155 if (sys::IsBigEndianHost) 156 sys::swapByteOrder(result); 157 return result; 158} 159 160/// Some primes between 2^63 and 2^64 for various uses. 161static const uint64_t k0 = 0xc3a5c85c97cb3127ULL; 162static const uint64_t k1 = 0xb492b66fbe98f273ULL; 163static const uint64_t k2 = 0x9ae16a3b2f90404fULL; 164static const uint64_t k3 = 0xc949d7c7509e6557ULL; 165 166/// Bitwise right rotate. 167/// Normally this will compile to a single instruction, especially if the 168/// shift is a manifest constant. 169inline uint64_t rotate(uint64_t val, size_t shift) { 170 // Avoid shifting by 64: doing so yields an undefined result. 171 return shift == 0 ? val : ((val >> shift) | (val << (64 - shift))); 172} 173 174inline uint64_t shift_mix(uint64_t val) { 175 return val ^ (val >> 47); 176} 177 178inline uint64_t hash_16_bytes(uint64_t low, uint64_t high) { 179 // Murmur-inspired hashing. 180 const uint64_t kMul = 0x9ddfea08eb382d69ULL; 181 uint64_t a = (low ^ high) * kMul; 182 a ^= (a >> 47); 183 uint64_t b = (high ^ a) * kMul; 184 b ^= (b >> 47); 185 b *= kMul; 186 return b; 187} 188 189inline uint64_t hash_1to3_bytes(const char *s, size_t len, uint64_t seed) { 190 uint8_t a = s[0]; 191 uint8_t b = s[len >> 1]; 192 uint8_t c = s[len - 1]; 193 uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8); 194 uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2); 195 return shift_mix(y * k2 ^ z * k3 ^ seed) * k2; 196} 197 198inline uint64_t hash_4to8_bytes(const char *s, size_t len, uint64_t seed) { 199 uint64_t a = fetch32(s); 200 return hash_16_bytes(len + (a << 3), seed ^ fetch32(s + len - 4)); 201} 202 203inline uint64_t hash_9to16_bytes(const char *s, size_t len, uint64_t seed) { 204 uint64_t a = fetch64(s); 205 uint64_t b = fetch64(s + len - 8); 206 return hash_16_bytes(seed ^ a, rotate(b + len, len)) ^ b; 207} 208 209inline uint64_t hash_17to32_bytes(const char *s, size_t len, uint64_t seed) { 210 uint64_t a = fetch64(s) * k1; 211 uint64_t b = fetch64(s + 8); 212 uint64_t c = fetch64(s + len - 8) * k2; 213 uint64_t d = fetch64(s + len - 16) * k0; 214 return hash_16_bytes(rotate(a - b, 43) + rotate(c ^ seed, 30) + d, 215 a + rotate(b ^ k3, 20) - c + len + seed); 216} 217 218inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) { 219 uint64_t z = fetch64(s + 24); 220 uint64_t a = fetch64(s) + (len + fetch64(s + len - 16)) * k0; 221 uint64_t b = rotate(a + z, 52); 222 uint64_t c = rotate(a, 37); 223 a += fetch64(s + 8); 224 c += rotate(a, 7); 225 a += fetch64(s + 16); 226 uint64_t vf = a + z; 227 uint64_t vs = b + rotate(a, 31) + c; 228 a = fetch64(s + 16) + fetch64(s + len - 32); 229 z = fetch64(s + len - 8); 230 b = rotate(a + z, 52); 231 c = rotate(a, 37); 232 a += fetch64(s + len - 24); 233 c += rotate(a, 7); 234 a += fetch64(s + len - 16); 235 uint64_t wf = a + z; 236 uint64_t ws = b + rotate(a, 31) + c; 237 uint64_t r = shift_mix((vf + ws) * k2 + (wf + vs) * k0); 238 return shift_mix((seed ^ (r * k0)) + vs) * k2; 239} 240 241inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) { 242 if (length >= 4 && length <= 8) 243 return hash_4to8_bytes(s, length, seed); 244 if (length > 8 && length <= 16) 245 return hash_9to16_bytes(s, length, seed); 246 if (length > 16 && length <= 32) 247 return hash_17to32_bytes(s, length, seed); 248 if (length > 32) 249 return hash_33to64_bytes(s, length, seed); 250 if (length != 0) 251 return hash_1to3_bytes(s, length, seed); 252 253 return k2 ^ seed; 254} 255 256/// The intermediate state used during hashing. 257/// Currently, the algorithm for computing hash codes is based on CityHash and 258/// keeps 56 bytes of arbitrary state. 259struct hash_state { 260 uint64_t h0 = 0, h1 = 0, h2 = 0, h3 = 0, h4 = 0, h5 = 0, h6 = 0; 261 262 /// Create a new hash_state structure and initialize it based on the 263 /// seed and the first 64-byte chunk. 264 /// This effectively performs the initial mix. 265 static hash_state create(const char *s, uint64_t seed) { 266 hash_state state = { 267 0, seed, hash_16_bytes(seed, k1), rotate(seed ^ k1, 49), 268 seed * k1, shift_mix(seed), 0 }; 269 state.h6 = hash_16_bytes(state.h4, state.h5); 270 state.mix(s); 271 return state; 272 } 273 274 /// Mix 32-bytes from the input sequence into the 16-bytes of 'a' 275 /// and 'b', including whatever is already in 'a' and 'b'. 276 static void mix_32_bytes(const char *s, uint64_t &a, uint64_t &b) { 277 a += fetch64(s); 278 uint64_t c = fetch64(s + 24); 279 b = rotate(b + a + c, 21); 280 uint64_t d = a; 281 a += fetch64(s + 8) + fetch64(s + 16); 282 b += rotate(a, 44) + d; 283 a += c; 284 } 285 286 /// Mix in a 64-byte buffer of data. 287 /// We mix all 64 bytes even when the chunk length is smaller, but we 288 /// record the actual length. 289 void mix(const char *s) { 290 h0 = rotate(h0 + h1 + h3 + fetch64(s + 8), 37) * k1; 291 h1 = rotate(h1 + h4 + fetch64(s + 48), 42) * k1; 292 h0 ^= h6; 293 h1 += h3 + fetch64(s + 40); 294 h2 = rotate(h2 + h5, 33) * k1; 295 h3 = h4 * k1; 296 h4 = h0 + h5; 297 mix_32_bytes(s, h3, h4); 298 h5 = h2 + h6; 299 h6 = h1 + fetch64(s + 16); 300 mix_32_bytes(s + 32, h5, h6); 301 std::swap(h2, h0); 302 } 303 304 /// Compute the final 64-bit hash code value based on the current 305 /// state and the length of bytes hashed. 306 uint64_t finalize(size_t length) { 307 return hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2, 308 hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0); 309 } 310}; 311 312 313/// A global, fixed seed-override variable. 314/// 315/// This variable can be set using the \see llvm::set_fixed_execution_seed 316/// function. See that function for details. Do not, under any circumstances, 317/// set or read this variable. 318extern uint64_t fixed_seed_override; 319 320inline uint64_t get_execution_seed() { 321 // FIXME: This needs to be a per-execution seed. This is just a placeholder 322 // implementation. Switching to a per-execution seed is likely to flush out 323 // instability bugs and so will happen as its own commit. 324 // 325 // However, if there is a fixed seed override set the first time this is 326 // called, return that instead of the per-execution seed. 327 const uint64_t seed_prime = 0xff51afd7ed558ccdULL; 328 static uint64_t seed = fixed_seed_override ? fixed_seed_override : seed_prime; 329 return seed; 330} 331 332 333/// Trait to indicate whether a type's bits can be hashed directly. 334/// 335/// A type trait which is true if we want to combine values for hashing by 336/// reading the underlying data. It is false if values of this type must 337/// first be passed to hash_value, and the resulting hash_codes combined. 338// 339// FIXME: We want to replace is_integral_or_enum and is_pointer here with 340// a predicate which asserts that comparing the underlying storage of two 341// values of the type for equality is equivalent to comparing the two values 342// for equality. For all the platforms we care about, this holds for integers 343// and pointers, but there are platforms where it doesn't and we would like to 344// support user-defined types which happen to satisfy this property. 345template <typename T> struct is_hashable_data 346 : std::integral_constant<bool, ((is_integral_or_enum<T>::value || 347 std::is_pointer<T>::value) && 348 64 % sizeof(T) == 0)> {}; 349 350// Special case std::pair to detect when both types are viable and when there 351// is no alignment-derived padding in the pair. This is a bit of a lie because 352// std::pair isn't truly POD, but it's close enough in all reasonable 353// implementations for our use case of hashing the underlying data. 354template <typename T, typename U> struct is_hashable_data<std::pair<T, U> > 355 : std::integral_constant<bool, (is_hashable_data<T>::value && 356 is_hashable_data<U>::value && 357 (sizeof(T) + sizeof(U)) == 358 sizeof(std::pair<T, U>))> {}; 359 360/// Helper to get the hashable data representation for a type. 361/// This variant is enabled when the type itself can be used. 362template <typename T> 363typename std::enable_if<is_hashable_data<T>::value, T>::type 364get_hashable_data(const T &value) { 365 return value; 366} 367/// Helper to get the hashable data representation for a type. 368/// This variant is enabled when we must first call hash_value and use the 369/// result as our data. 370template <typename T> 371typename std::enable_if<!is_hashable_data<T>::value, size_t>::type 372get_hashable_data(const T &value) { 373 using ::llvm::hash_value; 374 return hash_value(value); 375} 376 377/// Helper to store data from a value into a buffer and advance the 378/// pointer into that buffer. 379/// 380/// This routine first checks whether there is enough space in the provided 381/// buffer, and if not immediately returns false. If there is space, it 382/// copies the underlying bytes of value into the buffer, advances the 383/// buffer_ptr past the copied bytes, and returns true. 384template <typename T> 385bool store_and_advance(char *&buffer_ptr, char *buffer_end, const T& value, 386 size_t offset = 0) { 387 size_t store_size = sizeof(value) - offset; 388 if (buffer_ptr + store_size > buffer_end) 389 return false; 390 const char *value_data = reinterpret_cast<const char *>(&value); 391 memcpy(buffer_ptr, value_data + offset, store_size); 392 buffer_ptr += store_size; 393 return true; 394} 395 396/// Implement the combining of integral values into a hash_code. 397/// 398/// This overload is selected when the value type of the iterator is 399/// integral. Rather than computing a hash_code for each object and then 400/// combining them, this (as an optimization) directly combines the integers. 401template <typename InputIteratorT> 402hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) { 403 const uint64_t seed = get_execution_seed(); 404 char buffer[64], *buffer_ptr = buffer; 405 char *const buffer_end = std::end(buffer); 406 while (first != last && store_and_advance(buffer_ptr, buffer_end, 407 get_hashable_data(*first))) 408 ++first; 409 if (first == last) 410 return hash_short(buffer, buffer_ptr - buffer, seed); 411 assert(buffer_ptr == buffer_end); 412 413 hash_state state = state.create(buffer, seed); 414 size_t length = 64; 415 while (first != last) { 416 // Fill up the buffer. We don't clear it, which re-mixes the last round 417 // when only a partial 64-byte chunk is left. 418 buffer_ptr = buffer; 419 while (first != last && store_and_advance(buffer_ptr, buffer_end, 420 get_hashable_data(*first))) 421 ++first; 422 423 // Rotate the buffer if we did a partial fill in order to simulate doing 424 // a mix of the last 64-bytes. That is how the algorithm works when we 425 // have a contiguous byte sequence, and we want to emulate that here. 426 std::rotate(buffer, buffer_ptr, buffer_end); 427 428 // Mix this chunk into the current state. 429 state.mix(buffer); 430 length += buffer_ptr - buffer; 431 }; 432 433 return state.finalize(length); 434} 435 436/// Implement the combining of integral values into a hash_code. 437/// 438/// This overload is selected when the value type of the iterator is integral 439/// and when the input iterator is actually a pointer. Rather than computing 440/// a hash_code for each object and then combining them, this (as an 441/// optimization) directly combines the integers. Also, because the integers 442/// are stored in contiguous memory, this routine avoids copying each value 443/// and directly reads from the underlying memory. 444template <typename ValueT> 445typename std::enable_if<is_hashable_data<ValueT>::value, hash_code>::type 446hash_combine_range_impl(ValueT *first, ValueT *last) { 447 const uint64_t seed = get_execution_seed(); 448 const char *s_begin = reinterpret_cast<const char *>(first); 449 const char *s_end = reinterpret_cast<const char *>(last); 450 const size_t length = std::distance(s_begin, s_end); 451 if (length <= 64) 452 return hash_short(s_begin, length, seed); 453 454 const char *s_aligned_end = s_begin + (length & ~63); 455 hash_state state = state.create(s_begin, seed); 456 s_begin += 64; 457 while (s_begin != s_aligned_end) { 458 state.mix(s_begin); 459 s_begin += 64; 460 } 461 if (length & 63) 462 state.mix(s_end - 64); 463 464 return state.finalize(length); 465} 466 467} // namespace detail 468} // namespace hashing 469 470 471/// Compute a hash_code for a sequence of values. 472/// 473/// This hashes a sequence of values. It produces the same hash_code as 474/// 'hash_combine(a, b, c, ...)', but can run over arbitrary sized sequences 475/// and is significantly faster given pointers and types which can be hashed as 476/// a sequence of bytes. 477template <typename InputIteratorT> 478hash_code hash_combine_range(InputIteratorT first, InputIteratorT last) { 479 return ::llvm::hashing::detail::hash_combine_range_impl(first, last); 480} 481 482 483// Implementation details for hash_combine. 484namespace hashing { 485namespace detail { 486 487/// Helper class to manage the recursive combining of hash_combine 488/// arguments. 489/// 490/// This class exists to manage the state and various calls involved in the 491/// recursive combining of arguments used in hash_combine. It is particularly 492/// useful at minimizing the code in the recursive calls to ease the pain 493/// caused by a lack of variadic functions. 494struct hash_combine_recursive_helper { 495 char buffer[64] = {}; 496 hash_state state; 497 const uint64_t seed; 498 499public: 500 /// Construct a recursive hash combining helper. 501 /// 502 /// This sets up the state for a recursive hash combine, including getting 503 /// the seed and buffer setup. 504 hash_combine_recursive_helper() 505 : seed(get_execution_seed()) {} 506 507 /// Combine one chunk of data into the current in-flight hash. 508 /// 509 /// This merges one chunk of data into the hash. First it tries to buffer 510 /// the data. If the buffer is full, it hashes the buffer into its 511 /// hash_state, empties it, and then merges the new chunk in. This also 512 /// handles cases where the data straddles the end of the buffer. 513 template <typename T> 514 char *combine_data(size_t &length, char *buffer_ptr, char *buffer_end, T data) { 515 if (!store_and_advance(buffer_ptr, buffer_end, data)) { 516 // Check for skew which prevents the buffer from being packed, and do 517 // a partial store into the buffer to fill it. This is only a concern 518 // with the variadic combine because that formation can have varying 519 // argument types. 520 size_t partial_store_size = buffer_end - buffer_ptr; 521 memcpy(buffer_ptr, &data, partial_store_size); 522 523 // If the store fails, our buffer is full and ready to hash. We have to 524 // either initialize the hash state (on the first full buffer) or mix 525 // this buffer into the existing hash state. Length tracks the *hashed* 526 // length, not the buffered length. 527 if (length == 0) { 528 state = state.create(buffer, seed); 529 length = 64; 530 } else { 531 // Mix this chunk into the current state and bump length up by 64. 532 state.mix(buffer); 533 length += 64; 534 } 535 // Reset the buffer_ptr to the head of the buffer for the next chunk of 536 // data. 537 buffer_ptr = buffer; 538 539 // Try again to store into the buffer -- this cannot fail as we only 540 // store types smaller than the buffer. 541 if (!store_and_advance(buffer_ptr, buffer_end, data, 542 partial_store_size)) 543 llvm_unreachable("buffer smaller than stored type"); 544 } 545 return buffer_ptr; 546 } 547 548 /// Recursive, variadic combining method. 549 /// 550 /// This function recurses through each argument, combining that argument 551 /// into a single hash. 552 template <typename T, typename ...Ts> 553 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end, 554 const T &arg, const Ts &...args) { 555 buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg)); 556 557 // Recurse to the next argument. 558 return combine(length, buffer_ptr, buffer_end, args...); 559 } 560 561 /// Base case for recursive, variadic combining. 562 /// 563 /// The base case when combining arguments recursively is reached when all 564 /// arguments have been handled. It flushes the remaining buffer and 565 /// constructs a hash_code. 566 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end) { 567 // Check whether the entire set of values fit in the buffer. If so, we'll 568 // use the optimized short hashing routine and skip state entirely. 569 if (length == 0) 570 return hash_short(buffer, buffer_ptr - buffer, seed); 571 572 // Mix the final buffer, rotating it if we did a partial fill in order to 573 // simulate doing a mix of the last 64-bytes. That is how the algorithm 574 // works when we have a contiguous byte sequence, and we want to emulate 575 // that here. 576 std::rotate(buffer, buffer_ptr, buffer_end); 577 578 // Mix this chunk into the current state. 579 state.mix(buffer); 580 length += buffer_ptr - buffer; 581 582 return state.finalize(length); 583 } 584}; 585 586} // namespace detail 587} // namespace hashing 588 589/// Combine values into a single hash_code. 590/// 591/// This routine accepts a varying number of arguments of any type. It will 592/// attempt to combine them into a single hash_code. For user-defined types it 593/// attempts to call a \see hash_value overload (via ADL) for the type. For 594/// integer and pointer types it directly combines their data into the 595/// resulting hash_code. 596/// 597/// The result is suitable for returning from a user's hash_value 598/// *implementation* for their user-defined type. Consumers of a type should 599/// *not* call this routine, they should instead call 'hash_value'. 600template <typename ...Ts> hash_code hash_combine(const Ts &...args) { 601 // Recursively hash each argument using a helper class. 602 ::llvm::hashing::detail::hash_combine_recursive_helper helper; 603 return helper.combine(0, helper.buffer, helper.buffer + 64, args...); 604} 605 606// Implementation details for implementations of hash_value overloads provided 607// here. 608namespace hashing { 609namespace detail { 610 611/// Helper to hash the value of a single integer. 612/// 613/// Overloads for smaller integer types are not provided to ensure consistent 614/// behavior in the presence of integral promotions. Essentially, 615/// "hash_value('4')" and "hash_value('0' + 4)" should be the same. 616inline hash_code hash_integer_value(uint64_t value) { 617 // Similar to hash_4to8_bytes but using a seed instead of length. 618 const uint64_t seed = get_execution_seed(); 619 const char *s = reinterpret_cast<const char *>(&value); 620 const uint64_t a = fetch32(s); 621 return hash_16_bytes(seed + (a << 3), fetch32(s + 4)); 622} 623 624} // namespace detail 625} // namespace hashing 626 627// Declared and documented above, but defined here so that any of the hashing 628// infrastructure is available. 629template <typename T> 630typename std::enable_if<is_integral_or_enum<T>::value, hash_code>::type 631hash_value(T value) { 632 return ::llvm::hashing::detail::hash_integer_value( 633 static_cast<uint64_t>(value)); 634} 635 636// Declared and documented above, but defined here so that any of the hashing 637// infrastructure is available. 638template <typename T> hash_code hash_value(const T *ptr) { 639 return ::llvm::hashing::detail::hash_integer_value( 640 reinterpret_cast<uintptr_t>(ptr)); 641} 642 643// Declared and documented above, but defined here so that any of the hashing 644// infrastructure is available. 645template <typename T, typename U> 646hash_code hash_value(const std::pair<T, U> &arg) { 647 return hash_combine(arg.first, arg.second); 648} 649 650// Declared and documented above, but defined here so that any of the hashing 651// infrastructure is available. 652template <typename T> 653hash_code hash_value(const std::basic_string<T> &arg) { 654 return hash_combine_range(arg.begin(), arg.end()); 655} 656 657} // namespace llvm 658 659#endif 660