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/*
* Copyright 2019-2021 Diligent Graphics LLC
* Copyright 2015-2019 Egor Yusov
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* In no event and under no legal theory, whether in tort (including negligence),
* contract, or otherwise, unless required by applicable law (such as deliberate
* and grossly negligent acts) or agreed to in writing, shall any Contributor be
* liable for any damages, including any direct, indirect, special, incidental,
* or consequential damages of any character arising as a result of this License or
* out of the use or inability to use the software (including but not limited to damages
* for loss of goodwill, work stoppage, computer failure or malfunction, or any and
* all other commercial damages or losses), even if such Contributor has been advised
* of the possibility of such damages.
*/
#pragma once
#include <functional>
#include <memory>
#include <cstring>
#include "../../Primitives/interface/Errors.hpp"
#include "../../Platforms/Basic/interface/DebugUtilities.hpp"
#define LOG_HASH_CONFLICTS 1
namespace Diligent
{
// http://www.boost.org/doc/libs/1_35_0/doc/html/hash/combine.html
template <typename T>
void HashCombine(std::size_t& Seed, const T& Val)
{
Seed ^= std::hash<T>{}(Val) + 0x9e3779b9 + (Seed << 6) + (Seed >> 2);
}
template <typename FirstArgType, typename... RestArgsType>
void HashCombine(std::size_t& Seed, const FirstArgType& FirstArg, const RestArgsType&... RestArgs)
{
HashCombine(Seed, FirstArg);
HashCombine(Seed, RestArgs...); // recursive call using pack expansion syntax
}
template <typename... ArgsType>
std::size_t ComputeHash(const ArgsType&... Args)
{
std::size_t Seed = 0;
HashCombine(Seed, Args...);
return Seed;
}
template <typename CharType>
struct CStringHash
{
size_t operator()(const CharType* str) const
{
// http://www.cse.yorku.ca/~oz/hash.html
std::size_t Seed = 0;
while (size_t Ch = *(str++))
Seed = Seed * 65599 + Ch;
return Seed;
}
};
template <typename CharType>
struct CStringCompare
{
bool operator()(const CharType* str1, const CharType* str2) const
{
UNSUPPORTED("Template specialization is not implemented");
return false;
}
};
template <>
struct CStringCompare<Char>
{
bool operator()(const Char* str1, const Char* str2) const
{
return strcmp(str1, str2) == 0;
}
};
/// This helper structure is intended to facilitate using strings as a
/// hash table key. It provides constructors that can make a copy of the
/// source string or just keep a pointer to it, which enables searching in
/// the hash using raw const Char* pointers.
struct HashMapStringKey
{
public:
// This constructor can perform implicit const Char* -> HashMapStringKey
// conversion without copying the string.
HashMapStringKey(const Char* _Str, bool bMakeCopy = false) :
Str{_Str}
{
VERIFY(Str, "String pointer must not be null");
Ownership_Hash = CStringHash<Char>{}.operator()(Str) & HashMask;
if (bMakeCopy)
{
auto LenWithZeroTerm = strlen(Str) + 1;
auto* StrCopy = new char[LenWithZeroTerm];
memcpy(StrCopy, Str, LenWithZeroTerm);
Str = StrCopy;
Ownership_Hash |= StrOwnershipMask;
}
}
// Make this constructor explicit to avoid unintentional string copies
explicit HashMapStringKey(const String& Str) :
HashMapStringKey{Str.c_str(), true}
{
}
HashMapStringKey(HashMapStringKey&& Key) noexcept :
// clang-format off
Str {Key.Str},
Ownership_Hash{Key.Ownership_Hash}
// clang-format on
{
Key.Str = nullptr;
Key.Ownership_Hash = 0;
}
~HashMapStringKey()
{
if (Str != nullptr && (Ownership_Hash & StrOwnershipMask) != 0)
delete[] Str;
}
// Disable copy constuctor and assignments. The struct is designed
// to be initialized at creation time only.
// clang-format off
HashMapStringKey (const HashMapStringKey&) = delete;
HashMapStringKey& operator=(const HashMapStringKey&) = delete;
HashMapStringKey& operator=(HashMapStringKey&&) = delete;
// clang-format on
bool operator==(const HashMapStringKey& RHS) const
{
if (Str == RHS.Str)
return true;
if (Str == nullptr)
{
VERIFY_EXPR(RHS.Str != nullptr);
return false;
}
else if (RHS.Str == nullptr)
{
VERIFY_EXPR(Str != nullptr);
return false;
}
auto Hash = GetHash();
auto RHSHash = RHS.GetHash();
if (Hash != RHSHash)
{
VERIFY_EXPR(strcmp(Str, RHS.Str) != 0);
return false;
}
bool IsEqual = strcmp(Str, RHS.Str) == 0;
#if LOG_HASH_CONFLICTS
if (!IsEqual && Hash == RHSHash)
{
LOG_WARNING_MESSAGE("Unequal strings \"", Str, "\" and \"", RHS.Str,
"\" have the same hash. You may want to use a better hash function. "
"You may disable this warning by defining LOG_HASH_CONFLICTS to 0");
}
#endif
return IsEqual;
}
bool operator!=(const HashMapStringKey& RHS) const
{
return !(*this == RHS);
}
size_t GetHash() const
{
return Ownership_Hash & HashMask;
}
const Char* GetStr() const
{
return Str;
}
struct Hasher
{
size_t operator()(const HashMapStringKey& Key) const
{
return Key.GetHash();
}
};
protected:
static constexpr size_t StrOwnershipBit = sizeof(size_t) * 8 - 1;
static constexpr size_t StrOwnershipMask = size_t{1} << StrOwnershipBit;
static constexpr size_t HashMask = ~StrOwnershipMask;
const Char* Str = nullptr;
// We will use top bit of the hash to indicate if we own the pointer
size_t Ownership_Hash = 0;
};
} // namespace Diligent
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