| //===-- llvm/ADT/Hashing.h - Utilities for hashing --------------*- C++ -*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements the newly proposed standard C++ interfaces for hashing |
| // arbitrary data and building hash functions for user-defined types. This |
| // interface was originally proposed in N3333[1] and is currently under review |
| // for inclusion in a future TR and/or standard. |
| // |
| // The primary interfaces provide are comprised of one type and three functions: |
| // |
| // -- 'hash_code' class is an opaque type representing the hash code for some |
| // data. It is the intended product of hashing, and can be used to implement |
| // hash tables, checksumming, and other common uses of hashes. It is not an |
| // integer type (although it can be converted to one) because it is risky |
| // to assume much about the internals of a hash_code. In particular, each |
| // execution of the program has a high probability of producing a different |
| // hash_code for a given input. Thus their values are not stable to save or |
| // persist, and should only be used during the execution for the |
| // construction of hashing datastructures. |
| // |
| // -- 'hash_value' is a function designed to be overloaded for each |
| // user-defined type which wishes to be used within a hashing context. It |
| // should be overloaded within the user-defined type's namespace and found |
| // via ADL. Overloads for primitive types are provided by this library. |
| // |
| // -- 'hash_combine' and 'hash_combine_range' are functions designed to aid |
| // programmers in easily and intuitively combining a set of data into |
| // a single hash_code for their object. They should only logically be used |
| // within the implementation of a 'hash_value' routine or similar context. |
| // |
| // Note that 'hash_combine_range' contains very special logic for hashing |
| // a contiguous array of integers or pointers. This logic is *extremely* fast, |
| // on a modern Intel "Gainestown" Xeon (Nehalem uarch) @2.2 GHz, these were |
| // benchmarked at over 6.5 GiB/s for large keys, and <20 cycles/hash for keys |
| // under 32-bytes. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_ADT_HASHING_H |
| #define LLVM_ADT_HASHING_H |
| |
| #include "llvm/Support/DataTypes.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/SwapByteOrder.h" |
| #include "llvm/Support/type_traits.h" |
| #include <algorithm> |
| #include <cassert> |
| #include <cstring> |
| #include <string> |
| #include <utility> |
| |
| namespace llvm { |
| |
| /// An opaque object representing a hash code. |
| /// |
| /// This object represents the result of hashing some entity. It is intended to |
| /// be used to implement hashtables or other hashing-based data structures. |
| /// While it wraps and exposes a numeric value, this value should not be |
| /// trusted to be stable or predictable across processes or executions. |
| /// |
| /// In order to obtain the hash_code for an object 'x': |
| /// \code |
| /// using llvm::hash_value; |
| /// llvm::hash_code code = hash_value(x); |
| /// \endcode |
| class hash_code { |
| size_t value; |
| |
| public: |
| /// Default construct a hash_code. |
| /// Note that this leaves the value uninitialized. |
| hash_code() = default; |
| |
| /// Form a hash code directly from a numerical value. |
| hash_code(size_t value) : value(value) {} |
| |
| /// Convert the hash code to its numerical value for use. |
| /*explicit*/ operator size_t() const { return value; } |
| |
| friend bool operator==(const hash_code &lhs, const hash_code &rhs) { |
| return lhs.value == rhs.value; |
| } |
| friend bool operator!=(const hash_code &lhs, const hash_code &rhs) { |
| return lhs.value != rhs.value; |
| } |
| |
| /// Allow a hash_code to be directly run through hash_value. |
| friend size_t hash_value(const hash_code &code) { return code.value; } |
| }; |
| |
| /// Compute a hash_code for any integer value. |
| /// |
| /// Note that this function is intended to compute the same hash_code for |
| /// a particular value without regard to the pre-promotion type. This is in |
| /// contrast to hash_combine which may produce different hash_codes for |
| /// differing argument types even if they would implicit promote to a common |
| /// type without changing the value. |
| template <typename T> |
| typename std::enable_if<is_integral_or_enum<T>::value, hash_code>::type |
| hash_value(T value); |
| |
| /// Compute a hash_code for a pointer's address. |
| /// |
| /// N.B.: This hashes the *address*. Not the value and not the type. |
| template <typename T> hash_code hash_value(const T *ptr); |
| |
| /// Compute a hash_code for a pair of objects. |
| template <typename T, typename U> |
| hash_code hash_value(const std::pair<T, U> &arg); |
| |
| /// Compute a hash_code for a standard string. |
| template <typename T> |
| hash_code hash_value(const std::basic_string<T> &arg); |
| |
| |
| /// Override the execution seed with a fixed value. |
| /// |
| /// This hashing library uses a per-execution seed designed to change on each |
| /// run with high probability in order to ensure that the hash codes are not |
| /// attackable and to ensure that output which is intended to be stable does |
| /// not rely on the particulars of the hash codes produced. |
| /// |
| /// That said, there are use cases where it is important to be able to |
| /// reproduce *exactly* a specific behavior. To that end, we provide a function |
| /// which will forcibly set the seed to a fixed value. This must be done at the |
| /// start of the program, before any hashes are computed. Also, it cannot be |
| /// undone. This makes it thread-hostile and very hard to use outside of |
| /// immediately on start of a simple program designed for reproducible |
| /// behavior. |
| void set_fixed_execution_hash_seed(uint64_t fixed_value); |
| |
| |
| // All of the implementation details of actually computing the various hash |
| // code values are held within this namespace. These routines are included in |
| // the header file mainly to allow inlining and constant propagation. |
| namespace hashing { |
| namespace detail { |
| |
| inline uint64_t fetch64(const char *p) { |
| uint64_t result; |
| memcpy(&result, p, sizeof(result)); |
| if (sys::IsBigEndianHost) |
| sys::swapByteOrder(result); |
| return result; |
| } |
| |
| inline uint32_t fetch32(const char *p) { |
| uint32_t result; |
| memcpy(&result, p, sizeof(result)); |
| if (sys::IsBigEndianHost) |
| sys::swapByteOrder(result); |
| return result; |
| } |
| |
| /// Some primes between 2^63 and 2^64 for various uses. |
| static const uint64_t k0 = 0xc3a5c85c97cb3127ULL; |
| static const uint64_t k1 = 0xb492b66fbe98f273ULL; |
| static const uint64_t k2 = 0x9ae16a3b2f90404fULL; |
| static const uint64_t k3 = 0xc949d7c7509e6557ULL; |
| |
| /// Bitwise right rotate. |
| /// Normally this will compile to a single instruction, especially if the |
| /// shift is a manifest constant. |
| inline uint64_t rotate(uint64_t val, size_t shift) { |
| // Avoid shifting by 64: doing so yields an undefined result. |
| return shift == 0 ? val : ((val >> shift) | (val << (64 - shift))); |
| } |
| |
| inline uint64_t shift_mix(uint64_t val) { |
| return val ^ (val >> 47); |
| } |
| |
| inline uint64_t hash_16_bytes(uint64_t low, uint64_t high) { |
| // Murmur-inspired hashing. |
| const uint64_t kMul = 0x9ddfea08eb382d69ULL; |
| uint64_t a = (low ^ high) * kMul; |
| a ^= (a >> 47); |
| uint64_t b = (high ^ a) * kMul; |
| b ^= (b >> 47); |
| b *= kMul; |
| return b; |
| } |
| |
| inline uint64_t hash_1to3_bytes(const char *s, size_t len, uint64_t seed) { |
| uint8_t a = s[0]; |
| uint8_t b = s[len >> 1]; |
| uint8_t c = s[len - 1]; |
| uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8); |
| uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2); |
| return shift_mix(y * k2 ^ z * k3 ^ seed) * k2; |
| } |
| |
| inline uint64_t hash_4to8_bytes(const char *s, size_t len, uint64_t seed) { |
| uint64_t a = fetch32(s); |
| return hash_16_bytes(len + (a << 3), seed ^ fetch32(s + len - 4)); |
| } |
| |
| inline uint64_t hash_9to16_bytes(const char *s, size_t len, uint64_t seed) { |
| uint64_t a = fetch64(s); |
| uint64_t b = fetch64(s + len - 8); |
| return hash_16_bytes(seed ^ a, rotate(b + len, len)) ^ b; |
| } |
| |
| inline uint64_t hash_17to32_bytes(const char *s, size_t len, uint64_t seed) { |
| uint64_t a = fetch64(s) * k1; |
| uint64_t b = fetch64(s + 8); |
| uint64_t c = fetch64(s + len - 8) * k2; |
| uint64_t d = fetch64(s + len - 16) * k0; |
| return hash_16_bytes(rotate(a - b, 43) + rotate(c ^ seed, 30) + d, |
| a + rotate(b ^ k3, 20) - c + len + seed); |
| } |
| |
| inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) { |
| uint64_t z = fetch64(s + 24); |
| uint64_t a = fetch64(s) + (len + fetch64(s + len - 16)) * k0; |
| uint64_t b = rotate(a + z, 52); |
| uint64_t c = rotate(a, 37); |
| a += fetch64(s + 8); |
| c += rotate(a, 7); |
| a += fetch64(s + 16); |
| uint64_t vf = a + z; |
| uint64_t vs = b + rotate(a, 31) + c; |
| a = fetch64(s + 16) + fetch64(s + len - 32); |
| z = fetch64(s + len - 8); |
| b = rotate(a + z, 52); |
| c = rotate(a, 37); |
| a += fetch64(s + len - 24); |
| c += rotate(a, 7); |
| a += fetch64(s + len - 16); |
| uint64_t wf = a + z; |
| uint64_t ws = b + rotate(a, 31) + c; |
| uint64_t r = shift_mix((vf + ws) * k2 + (wf + vs) * k0); |
| return shift_mix((seed ^ (r * k0)) + vs) * k2; |
| } |
| |
| inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) { |
| if (length >= 4 && length <= 8) |
| return hash_4to8_bytes(s, length, seed); |
| if (length > 8 && length <= 16) |
| return hash_9to16_bytes(s, length, seed); |
| if (length > 16 && length <= 32) |
| return hash_17to32_bytes(s, length, seed); |
| if (length > 32) |
| return hash_33to64_bytes(s, length, seed); |
| if (length != 0) |
| return hash_1to3_bytes(s, length, seed); |
| |
| return k2 ^ seed; |
| } |
| |
| /// The intermediate state used during hashing. |
| /// Currently, the algorithm for computing hash codes is based on CityHash and |
| /// keeps 56 bytes of arbitrary state. |
| struct hash_state { |
| uint64_t h0 = 0, h1 = 0, h2 = 0, h3 = 0, h4 = 0, h5 = 0, h6 = 0; |
| |
| /// Create a new hash_state structure and initialize it based on the |
| /// seed and the first 64-byte chunk. |
| /// This effectively performs the initial mix. |
| static hash_state create(const char *s, uint64_t seed) { |
| hash_state state = { |
| 0, seed, hash_16_bytes(seed, k1), rotate(seed ^ k1, 49), |
| seed * k1, shift_mix(seed), 0 }; |
| state.h6 = hash_16_bytes(state.h4, state.h5); |
| state.mix(s); |
| return state; |
| } |
| |
| /// Mix 32-bytes from the input sequence into the 16-bytes of 'a' |
| /// and 'b', including whatever is already in 'a' and 'b'. |
| static void mix_32_bytes(const char *s, uint64_t &a, uint64_t &b) { |
| a += fetch64(s); |
| uint64_t c = fetch64(s + 24); |
| b = rotate(b + a + c, 21); |
| uint64_t d = a; |
| a += fetch64(s + 8) + fetch64(s + 16); |
| b += rotate(a, 44) + d; |
| a += c; |
| } |
| |
| /// Mix in a 64-byte buffer of data. |
| /// We mix all 64 bytes even when the chunk length is smaller, but we |
| /// record the actual length. |
| void mix(const char *s) { |
| h0 = rotate(h0 + h1 + h3 + fetch64(s + 8), 37) * k1; |
| h1 = rotate(h1 + h4 + fetch64(s + 48), 42) * k1; |
| h0 ^= h6; |
| h1 += h3 + fetch64(s + 40); |
| h2 = rotate(h2 + h5, 33) * k1; |
| h3 = h4 * k1; |
| h4 = h0 + h5; |
| mix_32_bytes(s, h3, h4); |
| h5 = h2 + h6; |
| h6 = h1 + fetch64(s + 16); |
| mix_32_bytes(s + 32, h5, h6); |
| std::swap(h2, h0); |
| } |
| |
| /// Compute the final 64-bit hash code value based on the current |
| /// state and the length of bytes hashed. |
| uint64_t finalize(size_t length) { |
| return hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2, |
| hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0); |
| } |
| }; |
| |
| |
| /// A global, fixed seed-override variable. |
| /// |
| /// This variable can be set using the \see llvm::set_fixed_execution_seed |
| /// function. See that function for details. Do not, under any circumstances, |
| /// set or read this variable. |
| extern uint64_t fixed_seed_override; |
| |
| inline uint64_t get_execution_seed() { |
| // FIXME: This needs to be a per-execution seed. This is just a placeholder |
| // implementation. Switching to a per-execution seed is likely to flush out |
| // instability bugs and so will happen as its own commit. |
| // |
| // However, if there is a fixed seed override set the first time this is |
| // called, return that instead of the per-execution seed. |
| const uint64_t seed_prime = 0xff51afd7ed558ccdULL; |
| static uint64_t seed = fixed_seed_override ? fixed_seed_override : seed_prime; |
| return seed; |
| } |
| |
| |
| /// Trait to indicate whether a type's bits can be hashed directly. |
| /// |
| /// A type trait which is true if we want to combine values for hashing by |
| /// reading the underlying data. It is false if values of this type must |
| /// first be passed to hash_value, and the resulting hash_codes combined. |
| // |
| // FIXME: We want to replace is_integral_or_enum and is_pointer here with |
| // a predicate which asserts that comparing the underlying storage of two |
| // values of the type for equality is equivalent to comparing the two values |
| // for equality. For all the platforms we care about, this holds for integers |
| // and pointers, but there are platforms where it doesn't and we would like to |
| // support user-defined types which happen to satisfy this property. |
| template <typename T> struct is_hashable_data |
| : std::integral_constant<bool, ((is_integral_or_enum<T>::value || |
| std::is_pointer<T>::value) && |
| 64 % sizeof(T) == 0)> {}; |
| |
| // Special case std::pair to detect when both types are viable and when there |
| // is no alignment-derived padding in the pair. This is a bit of a lie because |
| // std::pair isn't truly POD, but it's close enough in all reasonable |
| // implementations for our use case of hashing the underlying data. |
| template <typename T, typename U> struct is_hashable_data<std::pair<T, U> > |
| : std::integral_constant<bool, (is_hashable_data<T>::value && |
| is_hashable_data<U>::value && |
| (sizeof(T) + sizeof(U)) == |
| sizeof(std::pair<T, U>))> {}; |
| |
| /// Helper to get the hashable data representation for a type. |
| /// This variant is enabled when the type itself can be used. |
| template <typename T> |
| typename std::enable_if<is_hashable_data<T>::value, T>::type |
| get_hashable_data(const T &value) { |
| return value; |
| } |
| /// Helper to get the hashable data representation for a type. |
| /// This variant is enabled when we must first call hash_value and use the |
| /// result as our data. |
| template <typename T> |
| typename std::enable_if<!is_hashable_data<T>::value, size_t>::type |
| get_hashable_data(const T &value) { |
| using ::llvm::hash_value; |
| return hash_value(value); |
| } |
| |
| /// Helper to store data from a value into a buffer and advance the |
| /// pointer into that buffer. |
| /// |
| /// This routine first checks whether there is enough space in the provided |
| /// buffer, and if not immediately returns false. If there is space, it |
| /// copies the underlying bytes of value into the buffer, advances the |
| /// buffer_ptr past the copied bytes, and returns true. |
| template <typename T> |
| bool store_and_advance(char *&buffer_ptr, char *buffer_end, const T& value, |
| size_t offset = 0) { |
| size_t store_size = sizeof(value) - offset; |
| if (buffer_ptr + store_size > buffer_end) |
| return false; |
| const char *value_data = reinterpret_cast<const char *>(&value); |
| memcpy(buffer_ptr, value_data + offset, store_size); |
| buffer_ptr += store_size; |
| return true; |
| } |
| |
| /// Implement the combining of integral values into a hash_code. |
| /// |
| /// This overload is selected when the value type of the iterator is |
| /// integral. Rather than computing a hash_code for each object and then |
| /// combining them, this (as an optimization) directly combines the integers. |
| template <typename InputIteratorT> |
| hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) { |
| const uint64_t seed = get_execution_seed(); |
| char buffer[64], *buffer_ptr = buffer; |
| char *const buffer_end = std::end(buffer); |
| while (first != last && store_and_advance(buffer_ptr, buffer_end, |
| get_hashable_data(*first))) |
| ++first; |
| if (first == last) |
| return hash_short(buffer, buffer_ptr - buffer, seed); |
| assert(buffer_ptr == buffer_end); |
| |
| hash_state state = state.create(buffer, seed); |
| size_t length = 64; |
| while (first != last) { |
| // Fill up the buffer. We don't clear it, which re-mixes the last round |
| // when only a partial 64-byte chunk is left. |
| buffer_ptr = buffer; |
| while (first != last && store_and_advance(buffer_ptr, buffer_end, |
| get_hashable_data(*first))) |
| ++first; |
| |
| // Rotate the buffer if we did a partial fill in order to simulate doing |
| // a mix of the last 64-bytes. That is how the algorithm works when we |
| // have a contiguous byte sequence, and we want to emulate that here. |
| std::rotate(buffer, buffer_ptr, buffer_end); |
| |
| // Mix this chunk into the current state. |
| state.mix(buffer); |
| length += buffer_ptr - buffer; |
| }; |
| |
| return state.finalize(length); |
| } |
| |
| /// Implement the combining of integral values into a hash_code. |
| /// |
| /// This overload is selected when the value type of the iterator is integral |
| /// and when the input iterator is actually a pointer. Rather than computing |
| /// a hash_code for each object and then combining them, this (as an |
| /// optimization) directly combines the integers. Also, because the integers |
| /// are stored in contiguous memory, this routine avoids copying each value |
| /// and directly reads from the underlying memory. |
| template <typename ValueT> |
| typename std::enable_if<is_hashable_data<ValueT>::value, hash_code>::type |
| hash_combine_range_impl(ValueT *first, ValueT *last) { |
| const uint64_t seed = get_execution_seed(); |
| const char *s_begin = reinterpret_cast<const char *>(first); |
| const char *s_end = reinterpret_cast<const char *>(last); |
| const size_t length = std::distance(s_begin, s_end); |
| if (length <= 64) |
| return hash_short(s_begin, length, seed); |
| |
| const char *s_aligned_end = s_begin + (length & ~63); |
| hash_state state = state.create(s_begin, seed); |
| s_begin += 64; |
| while (s_begin != s_aligned_end) { |
| state.mix(s_begin); |
| s_begin += 64; |
| } |
| if (length & 63) |
| state.mix(s_end - 64); |
| |
| return state.finalize(length); |
| } |
| |
| } // namespace detail |
| } // namespace hashing |
| |
| |
| /// Compute a hash_code for a sequence of values. |
| /// |
| /// This hashes a sequence of values. It produces the same hash_code as |
| /// 'hash_combine(a, b, c, ...)', but can run over arbitrary sized sequences |
| /// and is significantly faster given pointers and types which can be hashed as |
| /// a sequence of bytes. |
| template <typename InputIteratorT> |
| hash_code hash_combine_range(InputIteratorT first, InputIteratorT last) { |
| return ::llvm::hashing::detail::hash_combine_range_impl(first, last); |
| } |
| |
| |
| // Implementation details for hash_combine. |
| namespace hashing { |
| namespace detail { |
| |
| /// Helper class to manage the recursive combining of hash_combine |
| /// arguments. |
| /// |
| /// This class exists to manage the state and various calls involved in the |
| /// recursive combining of arguments used in hash_combine. It is particularly |
| /// useful at minimizing the code in the recursive calls to ease the pain |
| /// caused by a lack of variadic functions. |
| struct hash_combine_recursive_helper { |
| char buffer[64] = {}; |
| hash_state state; |
| const uint64_t seed; |
| |
| public: |
| /// Construct a recursive hash combining helper. |
| /// |
| /// This sets up the state for a recursive hash combine, including getting |
| /// the seed and buffer setup. |
| hash_combine_recursive_helper() |
| : seed(get_execution_seed()) {} |
| |
| /// Combine one chunk of data into the current in-flight hash. |
| /// |
| /// This merges one chunk of data into the hash. First it tries to buffer |
| /// the data. If the buffer is full, it hashes the buffer into its |
| /// hash_state, empties it, and then merges the new chunk in. This also |
| /// handles cases where the data straddles the end of the buffer. |
| template <typename T> |
| char *combine_data(size_t &length, char *buffer_ptr, char *buffer_end, T data) { |
| if (!store_and_advance(buffer_ptr, buffer_end, data)) { |
| // Check for skew which prevents the buffer from being packed, and do |
| // a partial store into the buffer to fill it. This is only a concern |
| // with the variadic combine because that formation can have varying |
| // argument types. |
| size_t partial_store_size = buffer_end - buffer_ptr; |
| memcpy(buffer_ptr, &data, partial_store_size); |
| |
| // If the store fails, our buffer is full and ready to hash. We have to |
| // either initialize the hash state (on the first full buffer) or mix |
| // this buffer into the existing hash state. Length tracks the *hashed* |
| // length, not the buffered length. |
| if (length == 0) { |
| state = state.create(buffer, seed); |
| length = 64; |
| } else { |
| // Mix this chunk into the current state and bump length up by 64. |
| state.mix(buffer); |
| length += 64; |
| } |
| // Reset the buffer_ptr to the head of the buffer for the next chunk of |
| // data. |
| buffer_ptr = buffer; |
| |
| // Try again to store into the buffer -- this cannot fail as we only |
| // store types smaller than the buffer. |
| if (!store_and_advance(buffer_ptr, buffer_end, data, |
| partial_store_size)) |
| llvm_unreachable("buffer smaller than stored type"); |
| } |
| return buffer_ptr; |
| } |
| |
| /// Recursive, variadic combining method. |
| /// |
| /// This function recurses through each argument, combining that argument |
| /// into a single hash. |
| template <typename T, typename ...Ts> |
| hash_code combine(size_t length, char *buffer_ptr, char *buffer_end, |
| const T &arg, const Ts &...args) { |
| buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg)); |
| |
| // Recurse to the next argument. |
| return combine(length, buffer_ptr, buffer_end, args...); |
| } |
| |
| /// Base case for recursive, variadic combining. |
| /// |
| /// The base case when combining arguments recursively is reached when all |
| /// arguments have been handled. It flushes the remaining buffer and |
| /// constructs a hash_code. |
| hash_code combine(size_t length, char *buffer_ptr, char *buffer_end) { |
| // Check whether the entire set of values fit in the buffer. If so, we'll |
| // use the optimized short hashing routine and skip state entirely. |
| if (length == 0) |
| return hash_short(buffer, buffer_ptr - buffer, seed); |
| |
| // Mix the final buffer, rotating it if we did a partial fill in order to |
| // simulate doing a mix of the last 64-bytes. That is how the algorithm |
| // works when we have a contiguous byte sequence, and we want to emulate |
| // that here. |
| std::rotate(buffer, buffer_ptr, buffer_end); |
| |
| // Mix this chunk into the current state. |
| state.mix(buffer); |
| length += buffer_ptr - buffer; |
| |
| return state.finalize(length); |
| } |
| }; |
| |
| } // namespace detail |
| } // namespace hashing |
| |
| /// Combine values into a single hash_code. |
| /// |
| /// This routine accepts a varying number of arguments of any type. It will |
| /// attempt to combine them into a single hash_code. For user-defined types it |
| /// attempts to call a \see hash_value overload (via ADL) for the type. For |
| /// integer and pointer types it directly combines their data into the |
| /// resulting hash_code. |
| /// |
| /// The result is suitable for returning from a user's hash_value |
| /// *implementation* for their user-defined type. Consumers of a type should |
| /// *not* call this routine, they should instead call 'hash_value'. |
| template <typename ...Ts> hash_code hash_combine(const Ts &...args) { |
| // Recursively hash each argument using a helper class. |
| ::llvm::hashing::detail::hash_combine_recursive_helper helper; |
| return helper.combine(0, helper.buffer, helper.buffer + 64, args...); |
| } |
| |
| // Implementation details for implementations of hash_value overloads provided |
| // here. |
| namespace hashing { |
| namespace detail { |
| |
| /// Helper to hash the value of a single integer. |
| /// |
| /// Overloads for smaller integer types are not provided to ensure consistent |
| /// behavior in the presence of integral promotions. Essentially, |
| /// "hash_value('4')" and "hash_value('0' + 4)" should be the same. |
| inline hash_code hash_integer_value(uint64_t value) { |
| // Similar to hash_4to8_bytes but using a seed instead of length. |
| const uint64_t seed = get_execution_seed(); |
| const char *s = reinterpret_cast<const char *>(&value); |
| const uint64_t a = fetch32(s); |
| return hash_16_bytes(seed + (a << 3), fetch32(s + 4)); |
| } |
| |
| } // namespace detail |
| } // namespace hashing |
| |
| // Declared and documented above, but defined here so that any of the hashing |
| // infrastructure is available. |
| template <typename T> |
| typename std::enable_if<is_integral_or_enum<T>::value, hash_code>::type |
| hash_value(T value) { |
| return ::llvm::hashing::detail::hash_integer_value( |
| static_cast<uint64_t>(value)); |
| } |
| |
| // Declared and documented above, but defined here so that any of the hashing |
| // infrastructure is available. |
| template <typename T> hash_code hash_value(const T *ptr) { |
| return ::llvm::hashing::detail::hash_integer_value( |
| reinterpret_cast<uintptr_t>(ptr)); |
| } |
| |
| // Declared and documented above, but defined here so that any of the hashing |
| // infrastructure is available. |
| template <typename T, typename U> |
| hash_code hash_value(const std::pair<T, U> &arg) { |
| return hash_combine(arg.first, arg.second); |
| } |
| |
| // Declared and documented above, but defined here so that any of the hashing |
| // infrastructure is available. |
| template <typename T> |
| hash_code hash_value(const std::basic_string<T> &arg) { |
| return hash_combine_range(arg.begin(), arg.end()); |
| } |
| |
| } // namespace llvm |
| |
| #endif |