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AK: Initialize StringBuilder buffer in place

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Before this change, we'd construct a ByteBuffer for the internal buffer,
and then move-construct StringBuilder::m_buffer from it.

Due to ByteBuffer's inline capacity, this meant we had to memmove the
inline buffer an extra time for every StringBuilder created.
This commit is contained in:
Andreas Kling 2025-10-04 10:38:38 +02:00 committed by Andreas Kling
parent 1ec72de0a6
commit 72ea158f16
2 changed files with 11 additions and 13 deletions
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22
AK/StringBuilder.cpp
View file

@ -34,16 +34,12 @@ static constexpr size_t string_builder_prefix_size(StringBuilder::Mode mode)
VERIFY_NOT_REACHED();
}
static ErrorOr<StringBuilder::Buffer> create_buffer(StringBuilder::Mode mode, size_t capacity)
void StringBuilder::initialize_buffer(Mode mode, size_t capacity)
{
StringBuilder::Buffer buffer;
auto prefix_size = string_builder_prefix_size(mode);
if (capacity > StringBuilder::inline_capacity)
TRY(buffer.try_ensure_capacity(prefix_size + capacity));
TRY(buffer.try_resize(prefix_size));
return buffer;
m_buffer.ensure_capacity(prefix_size + capacity);
m_buffer.resize(prefix_size);
}
StringBuilder::StringBuilder()
@ -51,24 +47,24 @@ StringBuilder::StringBuilder()
static constexpr auto prefix_size = string_builder_prefix_size(DEFAULT_MODE);
static_assert(inline_capacity > prefix_size);
m_buffer.resize(prefix_size);
initialize_buffer(m_mode, inline_capacity);
}
StringBuilder::StringBuilder(size_t initial_capacity)
: m_buffer(MUST(create_buffer(DEFAULT_MODE, initial_capacity)))
{
initialize_buffer(m_mode, initial_capacity);
}
StringBuilder::StringBuilder(Mode mode)
: m_buffer(MUST(create_buffer(mode, inline_capacity)))
, m_mode(mode)
: m_mode(mode)
{
initialize_buffer(m_mode, inline_capacity);
}
StringBuilder::StringBuilder(Mode mode, size_t initial_capacity_in_code_units)
: m_buffer(MUST(create_buffer(mode, initial_capacity_in_code_units * (mode == Mode::UTF8 ? 1 : 2))))
, m_mode(mode)
: m_mode(mode)
{
initialize_buffer(mode, initial_capacity_in_code_units * (mode == Mode::UTF8 ? 1 : 2));
}
inline ErrorOr<void> StringBuilder::will_append(size_t size_in_bytes)

2
AK/StringBuilder.h
View file

@ -119,6 +119,8 @@ public:
Optional<Buffer::OutlineBuffer> leak_buffer_for_string_construction(Badge<Detail::Utf16StringData>) { return leak_buffer_for_string_construction(); }
private:
void initialize_buffer(Mode, size_t capacity);
Optional<Buffer::OutlineBuffer> leak_buffer_for_string_construction();
ErrorOr<void> will_append(size_t);