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construct/include/ircd/allocator/fixed.h
2023-02-05 12:06:42 -08:00

168 lines
4.4 KiB
C++

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2023 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.
#pragma once
#define HAVE_IRCD_ALLOCATOR_FIXED_H
namespace ircd::allocator
{
template<class T = char,
size_t = 512>
struct fixed;
}
/// The fixed allocator creates a block of data with a size known at compile-
/// time. This structure itself is the state object for the actual allocator
/// instance used in the container. Create an instance of this structure,
/// perhaps on your stack. Then specify the ircd::allocator::fixed::allocator
/// in the template for the container. Then pass a reference to the state
/// object as an argument to the container when constructing. STL containers
/// have an overloaded constructor for this when specializing the allocator
/// template as we are here.
///
template<class T,
size_t MAX>
struct ircd::allocator::fixed
:state
{
struct allocator;
using value = std::aligned_storage<sizeof(T), alignof(T)>;
std::array<word_t, MAX / 8> avail {{0}};
std::array<typename value::type, MAX> buf;
public:
bool in_range(const T *const &ptr) const
{
const auto base(reinterpret_cast<const T *>(buf.data()));
return ptr >= base && ptr < base + MAX;
}
allocator operator()();
operator allocator();
fixed()
{
static_cast<state &>(*this) =
{
MAX, avail.data()
};
}
};
/// The actual allocator template as used by the container.
///
/// This has to be a very light, small and copyable object which cannot hold
/// our actual memory or state (lest we just use dynamic allocation for that!)
/// which means we have to pass this a reference to our ircd::allocator::fixed
/// instance. We can do that through the container's custom-allocator overload
/// at its construction.
///
template<class T,
size_t SIZE>
struct ircd::allocator::fixed<T, SIZE>::allocator
{
using value_type = T;
using pointer = T *;
using const_pointer = const T *;
using reference = T &;
using const_reference = const T &;
using size_type = std::size_t;
using difference_type = std::ptrdiff_t;
fixed *s;
public:
template<class U> struct rebind
{
using other = typename fixed<U, SIZE>::allocator;
};
size_type max_size() const
{
return SIZE;
}
auto address(reference x) const
{
return &x;
}
auto address(const_reference x) const
{
return &x;
}
pointer
__attribute__((malloc, warn_unused_result))
allocate(std::nothrow_t, const size_type &n, const const_pointer &hint = nullptr)
{
const auto base(reinterpret_cast<pointer>(s->buf.data()));
const uint hintpos(hint? uint(hint - base) : uint(-1));
const pointer ret(base + s->state::allocate(std::nothrow, n, hintpos));
return s->in_range(ret)? ret : nullptr;
}
pointer
__attribute__((malloc, returns_nonnull, warn_unused_result))
allocate(const size_type &n, const const_pointer &hint = nullptr)
{
const auto base(reinterpret_cast<pointer>(s->buf.data()));
const uint hintpos(hint? uint(hint - base) : uint(-1));
return base + s->state::allocate(n, hintpos);
}
void deallocate(const pointer &p, const size_type &n)
{
const auto base(reinterpret_cast<pointer>(s->buf.data()));
s->state::deallocate(p - base, n);
}
template<class U,
size_t OTHER_SIZE = SIZE>
allocator(const typename fixed<U, OTHER_SIZE>::allocator &s) noexcept
:s{reinterpret_cast<fixed<T, SIZE> *>(s.s)}
{
static_assert(OTHER_SIZE == SIZE);
}
allocator(fixed &s) noexcept
:s{&s}
{}
allocator(allocator &&) = default;
allocator(const allocator &) = default;
friend bool operator==(const allocator &a, const allocator &b)
{
return &a == &b;
}
friend bool operator!=(const allocator &a, const allocator &b)
{
return &a == &b;
}
};
template<class T,
size_t SIZE>
inline typename ircd::allocator::fixed<T, SIZE>::allocator
ircd::allocator::fixed<T, SIZE>::operator()()
{
return ircd::allocator::fixed<T, SIZE>::allocator(*this);
}
template<class T,
size_t SIZE>
inline ircd::allocator::fixed<T, SIZE>::operator
allocator()
{
return ircd::allocator::fixed<T, SIZE>::allocator(*this);
}