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AK: Implement FlyString for the new String class

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This implements a FlyString that will de-duplicate String instances. The
FlyString will store the raw encoded data of the String instance: If the
String is a short string, FlyString holds the String::ShortString bytes;
otherwise FlyString holds a pointer to the Detail::StringData.

FlyString itself does not know about String's storage or how to refcount
its Detail::StringData. It defers to String to implement these details.
This commit is contained in:
Timothy Flynn 2023-01-11 08:26:49 -05:00 • committed by Andreas Kling
parent f49a65cb28
commit 1d4f287582
8 changed files with 445 additions and 1 deletions
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65
AK/String.cpp
View file

@ -5,6 +5,7 @@
*/
#include <AK/Checked.h>
#include <AK/FlyString.h>
#include <AK/Format.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>
@ -59,6 +60,9 @@ public:
return m_hash;
}
bool is_fly_string() const { return m_is_fly_string; }
void set_fly_string(bool is_fly_string) { m_is_fly_string = is_fly_string; }
private:
explicit StringData(size_t byte_count);
StringData(StringData const& superstring, size_t start, size_t byte_count);
@ -69,6 +73,7 @@ private:
mutable unsigned m_hash { 0 };
mutable bool m_has_hash { false };
bool m_substring { false };
bool m_is_fly_string { false };
u8 m_bytes_or_substring_data[0];
};
@ -95,6 +100,8 @@ StringData::StringData(StringData const& superstring, size_t start, size_t byte_
StringData::~StringData()
{
if (m_is_fly_string)
FlyString::did_destroy_fly_string_data({}, bytes_as_string_view());
if (m_substring)
substring_data().superstring->unref();
}
@ -255,6 +262,13 @@ bool String::operator==(String const& other) const
return bytes_as_string_view() == other.bytes_as_string_view();
}
bool String::operator==(FlyString const& other) const
{
if (reinterpret_cast<uintptr_t>(m_data) == other.data({}))
return true;
return bytes_as_string_view() == other.bytes_as_string_view();
}
bool String::operator==(StringView other) const
{
return bytes_as_string_view() == other;
@ -307,7 +321,7 @@ ErrorOr<String> String::replace(StringView needle, StringView replacement, Repla
bool String::is_short_string() const
{
return reinterpret_cast<uintptr_t>(m_data) & SHORT_STRING_FLAG;
return has_short_string_bit(reinterpret_cast<uintptr_t>(m_data));
}
ReadonlyBytes String::ShortString::bytes() const
@ -325,6 +339,55 @@ unsigned Traits<String>::hash(String const& string)
return string.hash();
}
String String::fly_string_data_to_string(Badge<FlyString>, uintptr_t const& data)
{
if (has_short_string_bit(data))
return String { *reinterpret_cast<ShortString const*>(&data) };
auto const* string_data = reinterpret_cast<Detail::StringData const*>(data);
return String { NonnullRefPtr<Detail::StringData>(*string_data) };
}
StringView String::fly_string_data_to_string_view(Badge<FlyString>, uintptr_t const& data)
{
if (has_short_string_bit(data)) {
auto const* short_string = reinterpret_cast<ShortString const*>(&data);
return short_string->bytes();
}
auto const* string_data = reinterpret_cast<Detail::StringData const*>(data);
return string_data->bytes_as_string_view();
}
uintptr_t String::to_fly_string_data(Badge<FlyString>) const
{
return reinterpret_cast<uintptr_t>(m_data);
}
void String::ref_fly_string_data(Badge<FlyString>, uintptr_t data)
{
if (has_short_string_bit(data))
return;
auto const* string_data = reinterpret_cast<Detail::StringData const*>(data);
string_data->ref();
}
void String::unref_fly_string_data(Badge<FlyString>, uintptr_t data)
{
if (has_short_string_bit(data))
return;
auto const* string_data = reinterpret_cast<Detail::StringData const*>(data);
string_data->unref();
}
void String::did_create_fly_string(Badge<FlyString>) const
{
VERIFY(!is_short_string());
m_data->set_fly_string(true);
}
DeprecatedString String::to_deprecated_string() const
{
return DeprecatedString(bytes_as_string_view());