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/*
* Copyright (c) 2016-2017, Intel Corporation
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Intel Corporation nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/**
* \file
* \brief Hashing utility functions.
*/
#ifndef UTIL_HASH_H
#define UTIL_HASH_H
#include <functional>
#include <string>
#include <type_traits>
#include <utility>
namespace ue2 {
namespace hash_detail {
inline
void hash_combine_impl(size_t &seed, size_t value) {
// Note: constants explicitly truncated on 32-bit platforms.
const size_t a = (size_t)0x0b4e0ef37bc32127ULL;
const size_t b = (size_t)0x318f07b0c8eb9be9ULL;
seed ^= value * a;
seed += b;
}
/** \brief Helper that determines whether std::begin() exists for T. */
template<typename T>
struct is_container_check {
private:
template<typename C>
static auto has_begin_function(const C &obj) -> decltype(std::begin(obj)) {
return std::begin(obj);
}
static void has_begin_function(...) {
return;
}
using has_begin_type = decltype(has_begin_function(std::declval<T>()));
public:
static const bool value = !std::is_void<has_begin_type>::value;
};
/** \brief Type trait to enable on whether T is a container. */
template<typename T>
struct is_container
: public ::std::integral_constant<bool, is_container_check<T>::value> {};
/** \brief Helper that determines whether T::hash() exists. */
template<typename T>
struct has_hash_member_check {
private:
template<typename C>
static auto has_hash_member_function(const C &obj) -> decltype(obj.hash()) {
return obj.hash();
}
static void has_hash_member_function(...) {
return;
}
using has_hash = decltype(has_hash_member_function(std::declval<T>()));
public:
static const bool value = !std::is_void<has_hash>::value;
};
/** \brief Type trait to enable on whether T::hash() exists. */
template<typename T>
struct has_hash_member
: public ::std::integral_constant<bool, has_hash_member_check<T>::value> {};
/** \brief Default hash: falls back to std::hash. */
template<typename T, typename Enable = void>
struct ue2_hash {
using decayed_type = typename std::decay<T>::type;
size_t operator()(const T &obj) const {
return std::hash<decayed_type>()(obj);
}
};
/** \brief Hash for std::pair. */
template<typename A, typename B>
struct ue2_hash<std::pair<A, B>, void> {
size_t operator()(const std::pair<A, B> &p) const {
size_t v = 0;
hash_combine_impl(v, ue2_hash<A>()(p.first));
hash_combine_impl(v, ue2_hash<B>()(p.second));
return v;
}
};
/** \brief Hash for any type that has a hash() member function. */
template<typename T>
struct ue2_hash<T, typename std::enable_if<has_hash_member<T>::value>::type> {
size_t operator()(const T &obj) const {
return obj.hash();
}
};
/**
* \brief Hash for any container type that supports std::begin().
*
* We exempt std::string as std::hash<std:string> is provided and quicker.
*/
template<typename T>
struct ue2_hash<T, typename std::enable_if<
is_container<T>::value &&
!std::is_same<typename std::decay<T>::type, std::string>::value &&
!has_hash_member<T>::value>::type> {
size_t operator()(const T &obj) const {
size_t v = 0;
for (const auto &elem : obj) {
using element_type = typename std::decay<decltype(elem)>::type;
hash_combine_impl(v, ue2_hash<element_type>()(elem));
}
return v;
}
};
/** \brief Hash for enum types. */
template<typename T>
struct ue2_hash<T, typename std::enable_if<std::is_enum<T>::value>::type> {
size_t operator()(const T &obj) const {
using utype = typename std::underlying_type<T>::type;
return ue2_hash<utype>()(static_cast<utype>(obj));
}
};
template<typename T>
void hash_combine(size_t &seed, const T &obj) {
hash_combine_impl(seed, ue2_hash<T>()(obj));
}
template<typename T>
void hash_build(size_t &v, const T &obj) {
hash_combine(v, obj);
}
template<typename T, typename... Args>
void hash_build(size_t &v, const T &obj, Args&&... args) {
hash_build(v, obj);
hash_build(v, args...); // recursive
}
} // namespace hash_detail
using hash_detail::hash_combine;
/**
* \brief Hasher for general use.
*
* Provides operators for most standard containers and falls back to
* std::hash<T>.
*/
struct ue2_hasher {
template<typename T>
size_t operator()(const T &obj) const {
return hash_detail::ue2_hash<T>()(obj);
}
};
/**
* \brief Computes the combined hash of all its arguments.
*
* Simply use:
*
* size_t hash = hash_all(a, b, c, d);
*
* Where a, b, c and d are hashable.
*/
template<typename... Args>
size_t hash_all(Args&&... args) {
size_t v = 0;
hash_detail::hash_build(v, args...);
return v;
}
} // namespace ue2
#endif // UTIL_HASH_H
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