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#pragma once
#include <util/generic/vector.h>
#include <util/ysaveload.h>
#include <type_traits>
// A vector preallocated on the stack.
// After exceeding the preconfigured stack space falls back to the heap.
// Publicly inherits TVector, but disallows swap (and hence shrink_to_fit, also operator= is reimplemented via copying).
//
// Inspired by: http://qt-project.org/doc/qt-4.8/qvarlengtharray.html#details
template <typename T, size_t CountOnStack = 256, bool UseFallbackAlloc = true, class Alloc = std::allocator<T>>
class TStackVec;
template <typename T, class Alloc = std::allocator<T>>
using TSmallVec = TStackVec<T, 16, true, Alloc>;
template <typename T, size_t CountOnStack = 256>
using TStackOnlyVec = TStackVec<T, CountOnStack, false>;
namespace NPrivate {
template <class Alloc, class StackAlloc, typename T, typename U>
struct TRebind {
typedef TReboundAllocator<Alloc, U> other;
};
template <class Alloc, class StackAlloc, typename T>
struct TRebind<Alloc, StackAlloc, T, T> {
typedef StackAlloc other;
};
template <typename T, size_t CountOnStack, bool UseFallbackAlloc, class Alloc = std::allocator<T>>
class TStackBasedAllocator: public Alloc {
public:
typedef TStackBasedAllocator<T, CountOnStack, UseFallbackAlloc, Alloc> TSelf;
using typename Alloc::difference_type;
using typename Alloc::size_type;
using typename Alloc::value_type;
template <class U>
struct rebind: public ::NPrivate::TRebind<Alloc, TSelf, T, U> {
};
public:
//NOTE: it is important to make this syntax; using =default will lead to memset https://godbolt.org/z/vTqzK9aWr
TStackBasedAllocator() noexcept {}
template <
typename... TArgs,
typename = std::enable_if_t<
std::is_constructible_v<Alloc, TArgs...>
>
>
TStackBasedAllocator(TArgs&&... args)
: Alloc(std::forward<TArgs>(args)...)
{}
T* allocate(size_type n) {
if (!IsStorageUsed && CountOnStack >= n) {
IsStorageUsed = true;
return reinterpret_cast<T*>(&StackBasedStorage[0]);
} else {
if constexpr (!UseFallbackAlloc) {
Y_FAIL(
"Stack storage overflow. Capacity: %d, requested: %d", (int)CountOnStack, int(n));
}
return FallbackAllocator().allocate(n);
}
}
void deallocate(T* p, size_type n) {
if (p >= reinterpret_cast<T*>(&StackBasedStorage[0]) &&
p < reinterpret_cast<T*>(&StackBasedStorage[CountOnStack])) {
Y_VERIFY(IsStorageUsed);
IsStorageUsed = false;
} else {
FallbackAllocator().deallocate(p, n);
}
}
private:
std::aligned_storage_t<sizeof(T), alignof(T)> StackBasedStorage[CountOnStack];
bool IsStorageUsed = false;
private:
Alloc& FallbackAllocator() noexcept {
return static_cast<Alloc&>(*this);
}
};
}
template <typename T, size_t CountOnStack, bool UseFallbackAlloc, class Alloc>
class TStackVec: public TVector<T, ::NPrivate::TStackBasedAllocator<T, CountOnStack, UseFallbackAlloc, TReboundAllocator<Alloc, T>>> {
private:
using TBase = TVector<T, ::NPrivate::TStackBasedAllocator<T, CountOnStack, UseFallbackAlloc, TReboundAllocator<Alloc, T>>>;
using TAllocator = typename TBase::allocator_type;
public:
using typename TBase::const_iterator;
using typename TBase::const_reverse_iterator;
using typename TBase::iterator;
using typename TBase::reverse_iterator;
using typename TBase::size_type;
using typename TBase::value_type;
public:
TStackVec(const TAllocator& alloc = TAllocator())
: TBase(alloc)
{
TBase::reserve(CountOnStack);
}
explicit TStackVec(size_type count, const TAllocator& alloc = TAllocator())
: TBase(alloc)
{
if (count <= CountOnStack) {
TBase::reserve(CountOnStack);
}
TBase::resize(count);
}
TStackVec(size_type count, const T& val, const TAllocator& alloc = TAllocator())
: TBase(alloc)
{
if (count <= CountOnStack) {
TBase::reserve(CountOnStack);
}
TBase::assign(count, val);
}
TStackVec(const TStackVec& src)
: TStackVec(src.begin(), src.end())
{
}
template <class A>
TStackVec(const TVector<T, A>& src)
: TStackVec(src.begin(), src.end())
{
}
TStackVec(std::initializer_list<T> il, const TAllocator& alloc = TAllocator())
: TStackVec(il.begin(), il.end(), alloc)
{
}
template <class TIter>
TStackVec(TIter first, TIter last, const TAllocator& alloc = TAllocator())
: TBase(alloc)
{
// NB(eeight) Since we want to call 'reserve' here, we cannot just delegate to TVector ctor.
// The best way to insert values afterwards is to call TVector::insert. However there is a caveat.
// In order to call this ctor of TVector, T needs to be just move-constructible. Insert however
// requires T to be move-assignable.
TBase::reserve(CountOnStack);
if constexpr (std::is_move_assignable_v<T>) {
// Fast path
TBase::insert(TBase::end(), first, last);
} else {
// Slow path.
for (; first != last; ++first) {
TBase::push_back(*first);
}
}
}
public:
void swap(TStackVec&) = delete;
void shrink_to_fit() = delete;
TStackVec& operator=(const TStackVec& src) {
TBase::assign(src.begin(), src.end());
return *this;
}
template <class A>
TStackVec& operator=(const TVector<T, A>& src) {
TBase::assign(src.begin(), src.end());
return *this;
}
TStackVec& operator=(std::initializer_list<T> il) {
TBase::assign(il.begin(), il.end());
return *this;
}
};
template <typename T, size_t CountOnStack, class Alloc>
class TSerializer<TStackVec<T, CountOnStack, true, Alloc>>: public TVectorSerializer<TStackVec<T, CountOnStack, true, Alloc>> {
};
template <typename T, size_t CountOnStack, class Alloc>
class TSerializer<TStackVec<T, CountOnStack, false, Alloc>> {
public:
static void Save(IOutputStream* rh, const TStackVec<T, CountOnStack, false, Alloc>& v) {
if constexpr (CountOnStack < 256) {
::Save(rh, (ui8)v.size());
} else {
::Save(rh, v.size());
}
::SaveArray(rh, v.data(), v.size());
}
static void Load(IInputStream* rh, TStackVec<T, CountOnStack, false, Alloc>& v) {
std::conditional_t<CountOnStack < 256, ui8, size_t> size;
::Load(rh, size);
v.resize(size);
::LoadPodArray(rh, v.data(), v.size());
}
};
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