71 lines
2.5 KiB
C++
71 lines
2.5 KiB
C++
// Copyright 2015 Citra Emulator Project
|
|
// Licensed under GPLv2 or any later version
|
|
// Refer to the license.txt file included.
|
|
|
|
#pragma once
|
|
|
|
#include <cstddef>
|
|
#include <cstring>
|
|
#include "common/cityhash.h"
|
|
#include "common/common_types.h"
|
|
|
|
namespace Common {
|
|
|
|
/**
|
|
* Computes a 64-bit hash over the specified block of data
|
|
* @param data Block of data to compute hash over
|
|
* @param len Length of data (in bytes) to compute hash over
|
|
* @returns 64-bit hash value that was computed over the data block
|
|
*/
|
|
static inline u64 ComputeHash64(const void* data, size_t len) {
|
|
return CityHash64(static_cast<const char*>(data), len);
|
|
}
|
|
|
|
/**
|
|
* Computes a 64-bit hash of a struct. In addition to being trivially copyable, it is also critical
|
|
* that either the struct includes no padding, or that any padding is initialized to a known value
|
|
* by memsetting the struct to 0 before filling it in.
|
|
*/
|
|
template <typename T>
|
|
static inline u64 ComputeStructHash64(const T& data) {
|
|
static_assert(std::is_trivially_copyable<T>(),
|
|
"Type passed to ComputeStructHash64 must be trivially copyable");
|
|
return ComputeHash64(&data, sizeof(data));
|
|
}
|
|
|
|
/// A helper template that ensures the padding in a struct is initialized by memsetting to 0.
|
|
template <typename T>
|
|
struct HashableStruct {
|
|
// In addition to being trivially copyable, T must also have a trivial default constructor,
|
|
// because any member initialization would be overridden by memset
|
|
static_assert(std::is_trivial<T>(), "Type passed to HashableStruct must be trivial");
|
|
/*
|
|
* We use a union because "implicitly-defined copy/move constructor for a union X copies the
|
|
* object representation of X." and "implicitly-defined copy assignment operator for a union X
|
|
* copies the object representation (3.9) of X." = Bytewise copy instead of memberwise copy.
|
|
* This is important because the padding bytes are included in the hash and comparison between
|
|
* objects.
|
|
*/
|
|
union {
|
|
T state;
|
|
};
|
|
|
|
HashableStruct() {
|
|
// Memset structure to zero padding bits, so that they will be deterministic when hashing
|
|
std::memset(&state, 0, sizeof(T));
|
|
}
|
|
|
|
bool operator==(const HashableStruct<T>& o) const {
|
|
return std::memcmp(&state, &o.state, sizeof(T)) == 0;
|
|
};
|
|
|
|
bool operator!=(const HashableStruct<T>& o) const {
|
|
return !(*this == o);
|
|
};
|
|
|
|
size_t Hash() const {
|
|
return Common::ComputeStructHash64(state);
|
|
}
|
|
};
|
|
|
|
} // namespace Common
|