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