mirror of https://github.com/bsnes-emu/bsnes.git
124 lines
2.8 KiB
C++
124 lines
2.8 KiB
C++
#pragma once
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/*****
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adaptive allocator
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sizeof(string) == SSO + 8
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aggressively tries to avoid heap allocations
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small strings are stored on the stack
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large strings are shared via copy-on-write
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SSO alone is very slow on large strings due to copying
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SSO alone is very slightly faster than this allocator on small strings
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COW alone is very slow on small strings due to heap allocations
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COW alone is very slightly faster than this allocator on large strings
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adaptive is thus very fast for all string sizes
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*****/
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namespace nall {
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string::string() : _data(nullptr), _capacity(SSO - 1), _size(0) {
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}
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template<typename T>
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auto string::get() -> T* {
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if(_capacity < SSO) return (T*)_text;
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if(*_refs > 1) _copy();
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return (T*)_data;
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}
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template<typename T>
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auto string::data() const -> const T* {
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if(_capacity < SSO) return (const T*)_text;
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return (const T*)_data;
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}
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auto string::reset() -> type& {
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if(_capacity >= SSO && !--*_refs) memory::free(_data);
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_data = nullptr;
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_capacity = SSO - 1;
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_size = 0;
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return *this;
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}
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auto string::reserve(uint capacity) -> type& {
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if(capacity <= _capacity) return *this;
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capacity = bit::round(capacity + 1) - 1;
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if(_capacity < SSO) {
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_capacity = capacity;
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_allocate();
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} else if(*_refs > 1) {
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_capacity = capacity;
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_copy();
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} else {
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_capacity = capacity;
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_resize();
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}
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return *this;
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}
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auto string::resize(uint size) -> type& {
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reserve(size);
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get()[_size = size] = 0;
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return *this;
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}
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auto string::operator=(const string& source) -> type& {
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if(&source == this) return *this;
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reset();
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if(source._capacity >= SSO) {
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_data = source._data;
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_refs = source._refs;
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_capacity = source._capacity;
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_size = source._size;
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++*_refs;
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} else {
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memory::copy(_text, source._text, SSO);
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_capacity = source._capacity;
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_size = source._size;
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}
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return *this;
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}
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auto string::operator=(string&& source) -> type& {
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if(&source == this) return *this;
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reset();
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memory::copy(this, &source, sizeof(string));
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source._data = nullptr;
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source._capacity = SSO - 1;
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source._size = 0;
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return *this;
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}
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//SSO -> COW
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auto string::_allocate() -> void {
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char _temp[SSO];
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memory::copy(_temp, _text, SSO);
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_data = (char*)memory::allocate(_capacity + 1 + sizeof(uint));
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memory::copy(_data, _temp, SSO);
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_refs = (uint*)(_data + _capacity + 1); //always aligned by 32 via reserve()
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*_refs = 1;
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}
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//COW -> Unique
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auto string::_copy() -> void {
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auto _temp = (char*)memory::allocate(_capacity + 1 + sizeof(uint));
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memory::copy(_temp, _data, _size = min(_capacity, _size));
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_temp[_size] = 0;
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--*_refs;
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_data = _temp;
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_refs = (uint*)(_data + _capacity + 1);
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*_refs = 1;
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}
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//COW -> Resize
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auto string::_resize() -> void {
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_data = (char*)memory::resize(_data, _capacity + 1 + sizeof(uint));
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_refs = (uint*)(_data + _capacity + 1);
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*_refs = 1;
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}
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}
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