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AK: Don't put element count next to heap-allocated data in FixedArray

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This not only makes code easier to follow but also makes it faster.
This commit is contained in:
Dan Klishch 2024-05-18 09:56:04 -04:00 committed by Andreas Kling
parent a0401b0d86
commit be36dbce7d
Notes: sideshowbarker 2024-07-17 05:13:53 +09:00 
Author: https://github.com/DanShaders
Commit: https://github.com/SerenityOS/serenity/commit/be36dbce7d
Pull-request: https://github.com/SerenityOS/serenity/pull/24360
1 changed files with 44 additions and 45 deletions
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89
AK/FixedArray.h
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@ -37,13 +37,12 @@ public:
{
if (size == 0)
return FixedArray<T>();
auto* new_storage = static_cast<Storage*>(kmalloc(storage_allocation_size(size)));
if (!new_storage)
auto* elements = reinterpret_cast<T*>(kmalloc(storage_allocation_size(size)));
if (!elements)
return Error::from_errno(ENOMEM);
new_storage->size = size;
for (size_t i = 0; i < size; ++i)
new (&new_storage->elements[i]) T();
return FixedArray<T>(new_storage);
new (&elements[i]) T();
return FixedArray<T>(size, elements);
}
static FixedArray<T> must_create_but_fixme_should_propagate_errors(size_t size)
@ -62,13 +61,12 @@ public:
{
if (span.size() == 0)
return FixedArray<T>();
auto* new_storage = static_cast<Storage*>(kmalloc(storage_allocation_size(span.size())));
if (!new_storage)
auto* elements = reinterpret_cast<T*>(kmalloc(storage_allocation_size(span.size())));
if (!elements)
return Error::from_errno(ENOMEM);
new_storage->size = span.size();
for (size_t i = 0; i < span.size(); ++i)
new (&new_storage->elements[i]) T(span[i]);
return FixedArray<T>(new_storage);
new (&elements[i]) T(span[i]);
return FixedArray<T>(span.size(), elements);
}
ErrorOr<FixedArray<T>> clone() const
@ -76,57 +74,55 @@ public:
return create(span());
}
static size_t storage_allocation_size(size_t size)
{
return sizeof(Storage) + size * sizeof(T);
}
// Nobody can ever use these functions, since it would be impossible to make them OOM-safe due to their signatures. We just explicitly delete them.
FixedArray(FixedArray<T> const&) = delete;
FixedArray<T>& operator=(FixedArray<T> const&) = delete;
FixedArray(FixedArray<T>&& other)
: m_storage(exchange(other.m_storage, nullptr))
: m_size(exchange(other.m_size, 0))
, m_elements(exchange(other.m_elements, nullptr))
{
}
FixedArray<T>& operator=(FixedArray<T>&& other)
{
m_storage = other.m_storage;
other.m_storage = nullptr;
if (this != &other) {
this->~FixedArray();
new (this) FixedArray<T>(move(other));
}
return *this;
}
~FixedArray()
{
if (!m_storage)
if (!m_elements)
return;
for (size_t i = 0; i < m_storage->size; ++i)
m_storage->elements[i].~T();
kfree_sized(m_storage, storage_allocation_size(m_storage->size));
m_storage = nullptr;
for (size_t i = 0; i < m_size; ++i)
m_elements[i].~T();
kfree_sized(m_elements, storage_allocation_size(m_size));
m_elements = nullptr;
}
size_t size() const { return m_storage ? m_storage->size : 0; }
size_t size() const { return m_size; }
bool is_empty() const { return size() == 0; }
T* data() { return m_storage ? m_storage->elements : nullptr; }
T const* data() const { return m_storage ? m_storage->elements : nullptr; }
T* data() { return m_elements; }
T const* data() const { return m_elements; }
T& at(size_t index)
{
VERIFY(index < m_storage->size);
return m_storage->elements[index];
VERIFY(index < m_size);
return m_elements[index];
}
T& unchecked_at(size_t index)
{
return m_storage->elements[index];
return m_elements[index];
}
T const& at(size_t index) const
{
VERIFY(index < m_storage->size);
return m_storage->elements[index];
VERIFY(index < m_size);
return m_elements[index];
}
T& operator[](size_t index)
@ -141,10 +137,10 @@ public:
bool contains_slow(T const& value) const
{
if (!m_storage)
if (!m_elements)
return false;
for (size_t i = 0; i < m_storage->size; ++i) {
if (m_storage->elements[i] == value)
for (size_t i = 0; i < m_size; ++i) {
if (m_elements[i] == value)
return true;
}
return false;
@ -152,15 +148,16 @@ public:
void swap(FixedArray<T>& other)
{
AK::swap(m_storage, other.m_storage);
AK::swap(m_size, other.m_size);
AK::swap(m_elements, other.m_elements);
}
void fill_with(T const& value)
{
if (!m_storage)
if (!m_elements)
return;
for (size_t i = 0; i < m_storage->size; ++i)
m_storage->elements[i] = value;
for (size_t i = 0; i < m_size; ++i)
m_elements[i] = value;
}
using Iterator = SimpleIterator<FixedArray, T>;
@ -176,17 +173,19 @@ public:
ReadonlySpan<T> span() const { return { data(), size() }; }
private:
struct Storage {
size_t size { 0 };
T elements[0];
};
static size_t storage_allocation_size(size_t size)
{
return size * sizeof(T);
}
FixedArray(Storage* storage)
: m_storage(storage)
FixedArray(size_t size, T* elements)
: m_size(size)
, m_elements(elements)
{
}
Storage* m_storage { nullptr };
size_t m_size { 0 };
T* m_elements { nullptr };
};
}