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AK: Implement a flyweight string for Utf16String

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Utf16FlyString more or less works exactly the same as FlyString. It will
store the raw encoded data of the string instance. If the string is a
short ASCII string, Utf16FlyString holds the ShortString bytes; else,
Utf16FlyString holds a pointer to the Utf16StringData.
This commit is contained in:
Timothy Flynn
2025-06-20 11:52:35 -04:00
committed by Tim Flynn
parent 2803d66d87
commit 7f069efbc4
Notes: github-actions[bot] 2025-07-18 16:47:19 +00:00 
Author: https://github.com/trflynn89
Commit: https://github.com/LadybirdBrowser/ladybird/commit/7f069efbc4a
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5388
Reviewed-by: https://github.com/shannonbooth ✅
9 changed files with 423 additions and 4 deletions
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15
AK/Utf16StringData.h
View File

@@ -16,6 +16,8 @@
namespace AK::Detail {
void did_destroy_utf16_fly_string_data(Badge<Detail::Utf16StringData>, Detail::Utf16StringData const&);
class Utf16StringData final : public RefCounted<Utf16StringData> {
public:
enum class StorageType : u8 {
@@ -33,7 +35,11 @@ public:
static NonnullRefPtr<Utf16StringData> from_utf32(Utf32View const&);
static NonnullRefPtr<Utf16StringData> from_string_builder(StringBuilder&);
~Utf16StringData() = default;
~Utf16StringData()
{
if (is_fly_string())
did_destroy_utf16_fly_string_data({}, *this);
}
[[nodiscard]] static constexpr size_t offset_of_string_storage()
{
@@ -47,6 +53,8 @@ public:
[[nodiscard]] ALWAYS_INLINE bool operator==(Utf16StringData const& other) const
{
if (is_fly_string() && other.is_fly_string())
return this == &other;
return utf16_view() == other.utf16_view();
}
@@ -99,6 +107,9 @@ public:
return view;
}
ALWAYS_INLINE void mark_as_fly_string(Badge<Utf16FlyString>) const { m_is_fly_string = true; }
[[nodiscard]] ALWAYS_INLINE bool is_fly_string() const { return m_is_fly_string; }
private:
ALWAYS_INLINE Utf16StringData(StorageType storage_type, size_t code_unit_length)
: m_length_in_code_units(code_unit_length)
@@ -130,6 +141,8 @@ private:
mutable u32 m_hash { 0 };
mutable bool m_has_hash { false };
mutable bool m_is_fly_string { false };
union {
char m_ascii_data[0];
char16_t m_utf16_data[0];