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BAN: String now uses union for its sso storage 

This allows String to shrink by 8 bytes since Variant's 8 index is
no longer stored in here.

This required me to make Strings max size one bit less, but that
should still be fine. There should never be strings with size of
over half of the computer's address space.
This commit is contained in:
Bananymous 2023-10-30 11:13:16 +02:00
parent a63006afaf
commit d5e0900cbb
2 changed files with 43 additions and 40 deletions
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69
BAN/BAN/String.cpp
View File

@ -1,6 +1,5 @@
#include <BAN/String.h>
#include <BAN/New.h>
#include <BAN/Variant.h>
namespace BAN
{
@ -32,8 +31,7 @@ namespace BAN
String& String::operator=(const String& other)
{
clear();
if (!other.fits_in_sso())
MUST(ensure_capacity(other.size()));
MUST(ensure_capacity(other.size()));
memcpy(data(), other.data(), other.size() + 1);
m_size = other.size();
return *this;
@ -43,14 +41,18 @@ namespace BAN
{
clear();
if (other.fits_in_sso())
if (other.has_sso())
memcpy(data(), other.data(), other.size() + 1);
else
m_storage = other.m_storage.get<GeneralStorage>();
{
m_storage.general_storage = other.m_storage.general_storage;
m_has_sso = false;
}
m_size = other.m_size;
other.m_size = 0;
other.m_storage = SSOStorage();
other.m_storage.sso_storage = SSOStorage();
other.m_has_sso = true;
return *this;
}
@ -58,8 +60,7 @@ namespace BAN
String& String::operator=(StringView other)
{
clear();
if (!fits_in_sso(other.size()))
MUST(ensure_capacity(other.size()));
MUST(ensure_capacity(other.size()));
memcpy(data(), other.data(), other.size());
m_size = other.size();
data()[m_size] = '\0';
@ -125,8 +126,9 @@ namespace BAN
{
if (!has_sso())
{
deallocator(m_storage.get<GeneralStorage>().data);
m_storage = SSOStorage();
deallocator(m_storage.general_storage.data);
m_storage.sso_storage = SSOStorage();
m_has_sso = true;
}
m_size = 0;
data()[m_size] = '\0';
@ -167,15 +169,6 @@ namespace BAN
return {};
}
// shrink general -> sso
if (!has_sso() && fits_in_sso(new_size))
{
char* data = m_storage.get<GeneralStorage>().data;
m_storage = SSOStorage();
memcpy(m_storage.get<SSOStorage>().storage, data, new_size);
deallocator(data);
}
m_size = new_size;
data()[m_size] = '\0';
return {};
@ -194,20 +187,21 @@ namespace BAN
if (fits_in_sso())
{
char* data = m_storage.get<GeneralStorage>().data;
m_storage = SSOStorage();
memcpy(m_storage.get<SSOStorage>().storage, data, m_size + 1);
char* data = m_storage.general_storage.data;
m_storage.sso_storage = SSOStorage();
m_has_sso = true;
memcpy(this->data(), data, m_size + 1);
deallocator(data);
return {};
}
GeneralStorage& storage = m_storage.get<GeneralStorage>();
GeneralStorage& storage = m_storage.general_storage;
if (storage.capacity == m_size)
return {};
char* new_data = (char*)allocator(m_size + 1);
if (new_data == nullptr)
return BAN::Error::from_errno(ENOMEM);
return Error::from_errno(ENOMEM);
memcpy(new_data, storage.data, m_size);
deallocator(storage.data);
@ -222,40 +216,45 @@ namespace BAN
{
if (has_sso())
return sso_capacity;
return m_storage.get<GeneralStorage>().capacity;
return m_storage.general_storage.capacity;
}
char* String::data()
{
if (has_sso())
return m_storage.get<SSOStorage>().storage;
return m_storage.get<GeneralStorage>().data;
return m_storage.sso_storage.data;
return m_storage.general_storage.data;
}
const char* String::data() const
{
if (has_sso())
return m_storage.get<SSOStorage>().storage;
return m_storage.get<GeneralStorage>().data;
return m_storage.sso_storage.data;
return m_storage.general_storage.data;
}
ErrorOr<void> String::ensure_capacity(size_type new_size)
{
if (m_size >= new_size || fits_in_sso(new_size))
if (m_size >= new_size)
return {};
if (has_sso() && fits_in_sso(new_size))
return {};
char* new_data = (char*)allocator(new_size + 1);
if (new_data == nullptr)
return BAN::Error::from_errno(ENOMEM);
return Error::from_errno(ENOMEM);
memcpy(new_data, data(), m_size + 1);
if (has_sso())
m_storage = GeneralStorage();
{
m_storage.general_storage = GeneralStorage();
m_has_sso = false;
}
else
deallocator(m_storage.get<GeneralStorage>().data);
deallocator(m_storage.general_storage.data);
auto& storage = m_storage.get<GeneralStorage>();
auto& storage = m_storage.general_storage;
storage.capacity = new_size;
storage.data = new_data;
@ -264,7 +263,7 @@ namespace BAN
bool String::has_sso() const
{
return m_storage.has<SSOStorage>();
return m_has_sso;
}
}

14
BAN/include/BAN/String.h
View File

@ -82,17 +82,21 @@ namespace BAN
private:
struct SSOStorage
{
char storage[sso_capacity + 1] {};
char data[sso_capacity + 1] {};
};
struct GeneralStorage
{
size_type capacity { 0 };
char* data;
size_type capacity { 0 };
char* data { nullptr };
};
private:
Variant<SSOStorage, GeneralStorage> m_storage { SSOStorage() };
size_type m_size { 0 };
union {
SSOStorage sso_storage;
GeneralStorage general_storage;
} m_storage { .sso_storage = SSOStorage() };
size_type m_size : sizeof(size_type) * 8 - 1 { 0 };
size_type m_has_sso : 1 { true };
};
template<typename... Args>