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Before this change, the global FlyString table looked like this: HashMap<StringView, Detail::StringBase> After this change, we have: HashTable<Detail::StringData const*, FlyStringTableHashTraits> The custom hash traits are used to extract the stored hash from StringData which avoids having to rehash the StringView repeatedly like we did before. This necessitated a handful of smaller changes to make it work.
133 lines
3.8 KiB
C++
133 lines
3.8 KiB
C++
/*
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* Copyright (c) 2023, Dan Klishch <danilklishch@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/RefCounted.h>
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#include <AK/kmalloc.h>
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namespace AK::Detail {
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class StringData final : public RefCounted<StringData> {
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public:
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static ErrorOr<NonnullRefPtr<StringData>> create_uninitialized(size_t byte_count, u8*& buffer)
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{
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VERIFY(byte_count);
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void* slot = malloc(allocation_size_for_string_data(byte_count));
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if (!slot) {
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return Error::from_errno(ENOMEM);
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}
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auto new_string_data = adopt_ref(*new (slot) StringData(byte_count));
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buffer = const_cast<u8*>(new_string_data->bytes().data());
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return new_string_data;
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}
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static ErrorOr<NonnullRefPtr<StringData>> create_substring(StringData const& superstring, size_t start, size_t byte_count)
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{
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// Strings of MAX_SHORT_STRING_BYTE_COUNT bytes or less should be handled by the String short string optimization.
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VERIFY(byte_count > MAX_SHORT_STRING_BYTE_COUNT);
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void* slot = malloc(sizeof(StringData) + sizeof(StringData::SubstringData));
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if (!slot) {
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return Error::from_errno(ENOMEM);
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}
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return adopt_ref(*new (slot) StringData(superstring, start, byte_count));
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}
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struct SubstringData {
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StringData const* superstring { nullptr };
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u32 start_offset { 0 };
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};
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void operator delete(void* ptr)
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{
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kfree_sized(ptr, allocation_size_for_string_data(static_cast<StringData const*>(ptr)->m_byte_count));
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}
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~StringData()
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{
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if (m_substring)
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substring_data().superstring->unref();
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if (m_is_fly_string)
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FlyString::did_destroy_fly_string_data({}, *this);
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}
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SubstringData const& substring_data() const
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{
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return *reinterpret_cast<SubstringData const*>(m_bytes_or_substring_data);
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}
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// NOTE: There is no guarantee about null-termination.
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ReadonlyBytes bytes() const
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{
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if (m_substring) {
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auto const& data = substring_data();
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return data.superstring->bytes().slice(data.start_offset, m_byte_count);
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}
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return { &m_bytes_or_substring_data[0], m_byte_count };
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}
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StringView bytes_as_string_view() const { return { bytes() }; }
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bool operator==(StringData const& other) const
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{
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return bytes_as_string_view() == other.bytes_as_string_view();
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}
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unsigned hash() const
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{
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if (!m_has_hash)
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compute_hash();
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return m_hash;
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}
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bool is_fly_string() const { return m_is_fly_string; }
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void set_fly_string(bool is_fly_string) const { m_is_fly_string = is_fly_string; }
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size_t byte_count() const { return m_byte_count; }
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private:
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static constexpr size_t allocation_size_for_string_data(size_t length)
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{
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return sizeof(StringData) + (sizeof(char) * length);
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}
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explicit StringData(size_t byte_count)
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: m_byte_count(byte_count)
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{
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}
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StringData(StringData const& superstring, size_t start, size_t byte_count)
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: m_byte_count(byte_count)
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, m_substring(true)
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{
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auto& data = const_cast<SubstringData&>(substring_data());
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data.start_offset = start;
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data.superstring = &superstring;
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superstring.ref();
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}
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void compute_hash() const
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{
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auto bytes = this->bytes();
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if (bytes.size() == 0)
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m_hash = 0;
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else
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m_hash = string_hash(reinterpret_cast<char const*>(bytes.data()), bytes.size());
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m_has_hash = true;
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}
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u32 m_byte_count { 0 };
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mutable unsigned m_hash { 0 };
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mutable bool m_has_hash { false };
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bool m_substring { false };
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mutable bool m_is_fly_string { false };
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alignas(SubstringData) u8 m_bytes_or_substring_data[0];
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};
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}
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