mirror of
https://github.com/matrix-construct/construct
synced 2024-12-25 06:53:58 +01:00
462 lines
13 KiB
C++
462 lines
13 KiB
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice is present in all copies. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_ALLOCATOR_H
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/// Suite of custom allocator templates for special behavior and optimization
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///
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/// These tools can be used as alternatives to the standard allocator. Most
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/// templates implement the std::allocator concept and can be used with
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/// std:: containers by specifying them in the container's template parameter.
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///
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namespace ircd::allocator
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{
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struct state;
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template<class T = char> struct dynamic;
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template<class T = char, size_t = 512> struct fixed;
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template<class T> struct node;
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};
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/// Internal state structure for some of these tools. This is a very small and
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/// simple interface to a bit array representing the availability of an element
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/// in a pool of elements. The actual array of the proper number of bits must
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/// be supplied by the user of the state. The allocator using this interface
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/// can use any strategy to flip these bits but the default next()/allocate()
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/// functions scan for the next available contiguous block of zero bits and
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/// then wrap around when reaching the end of the array. Once a full iteration
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/// of the array is made without finding satisfaction, an std::bad_alloc is
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/// thrown.
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///
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struct ircd::allocator::state
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{
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using word_t = unsigned long long;
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using size_type = std::size_t;
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size_t size { 0 };
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word_t *avail { nullptr };
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size_t last { 0 };
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static uint byte(const uint &i) { return i / (sizeof(word_t) * 8); }
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static uint bit(const uint &i) { return i % (sizeof(word_t) * 8); }
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static word_t mask(const uint &pos) { return word_t(1) << bit(pos); }
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bool test(const uint &pos) const { return avail[byte(pos)] & mask(pos); }
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void bts(const uint &pos) { avail[byte(pos)] |= mask(pos); }
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void btc(const uint &pos) { avail[byte(pos)] &= ~mask(pos); }
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uint next(const size_t &n) const;
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public:
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void deallocate(const uint &p, const size_t &n);
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uint allocate(const size_t &n, const uint &hint = -1);
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state(const size_t &size = 0,
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word_t *const &avail = nullptr)
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:size{size}
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,avail{avail}
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,last{0}
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{}
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};
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/// The fixed allocator creates a block of data with a size known at compile-
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/// time. This structure itself is the state object for the actual allocator
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/// instance used in the container. Create an instance of this structure,
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/// perhaps on your stack. Then specify the ircd::allocator::fixed::allocator
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/// in the template for the container. Then pass a reference to the state
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/// object as an argument to the container when constructing. STL containers
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/// have an overloaded constructor for this when specializing the allocator
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/// template as we are here.
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///
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template<class T,
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size_t max>
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struct ircd::allocator::fixed
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:state
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{
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struct allocator;
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using value = std::aligned_storage<sizeof(T), alignof(T)>;
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std::array<word_t, max / 8> avail {{0}};
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std::array<typename value::type, max> buf;
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public:
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allocator operator()();
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operator allocator();
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fixed()
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:state{max, avail.data()}
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{}
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};
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/// The actual allocator template as used by the container.
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///
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/// This has to be a very light, small and copyable object which cannot hold
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/// our actual memory or state (lest we just use dynamic allocation for that!)
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/// which means we have to pass this a reference to our ircd::allocator::fixed
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/// instance. We can do that through the container's custom-allocator overload
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/// at its construction.
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///
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template<class T,
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size_t size>
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struct ircd::allocator::fixed<T, size>::allocator
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{
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using value_type = T;
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using pointer = T *;
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using const_pointer = const T *;
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using reference = T &;
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using const_reference = const T &;
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using size_type = std::size_t;
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using difference_type = std::ptrdiff_t;
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fixed *s;
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public:
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template<class U, size_t S> struct rebind
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{
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using other = typename fixed<U, S>::allocator;
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};
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size_type max_size() const { return size; }
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auto address(reference x) const { return &x; }
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auto address(const_reference x) const { return &x; }
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pointer allocate(const size_type &n, const const_pointer &hint = nullptr)
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{
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const auto base(reinterpret_cast<pointer>(s->buf.data()));
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const uint hintpos(hint? hint - base : -1);
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return base + s->state::allocate(n, hintpos);
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}
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void deallocate(const pointer &p, const size_type &n)
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{
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const auto base(reinterpret_cast<pointer>(s->buf.data()));
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s->state::deallocate(p - base, n);
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}
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template<class U, size_t S>
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allocator(const typename fixed<U, S>::allocator &) noexcept
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:s{reinterpret_cast<fixed *>(s.s)}
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{}
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allocator(fixed &s) noexcept
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:s{&s}
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{}
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allocator(allocator &&) = default;
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allocator(const allocator &) = default;
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friend bool operator==(const allocator &a, const allocator &b)
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{
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return &a == &b;
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}
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friend bool operator!=(const allocator &a, const allocator &b)
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{
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return &a == &b;
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}
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};
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template<class T,
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size_t size>
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typename ircd::allocator::fixed<T, size>::allocator
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ircd::allocator::fixed<T, size>::operator()()
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{
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return { *this };
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}
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template<class T,
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size_t size>
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ircd::allocator::fixed<T, size>::operator
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allocator()
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{
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return { *this };
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}
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/// The dynamic allocator provides a pool of a fixed size known at runtime.
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///
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/// This allocator conducts a single new and delete for a pool allowing an STL
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/// container to operate without interacting with the rest of the system and
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/// without fragmentation. This is not as useful as the allocator::fixed in
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/// practice as the standard allocator is as good as this in many cases. This
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/// is still available as an analog to the fixed allocator in this suite.
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///
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template<class T>
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struct ircd::allocator::dynamic
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:state
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{
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struct allocator;
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size_t head_size, data_size;
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std::unique_ptr<uint8_t[]> arena;
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T *buf;
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public:
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allocator operator()();
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operator allocator();
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dynamic(const size_t &size)
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:state{size}
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,head_size{size / 8}
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,data_size{sizeof(T) * size + 16}
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,arena
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{
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new __attribute__((aligned(16))) uint8_t[head_size + data_size]
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}
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,buf
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{
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reinterpret_cast<T *>(arena.get() + head_size + (head_size % 16))
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}
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{
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state::avail = reinterpret_cast<word_t *>(arena.get());
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}
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};
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/// The actual template passed to containers for using the dynamic allocator.
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///
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/// See the notes for ircd::allocator::fixed::allocator for details.
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///
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template<class T>
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struct ircd::allocator::dynamic<T>::allocator
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{
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using value_type = T;
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using pointer = T *;
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using const_pointer = const T *;
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using reference = T &;
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using const_reference = const T &;
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using size_type = std::size_t;
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using difference_type = std::ptrdiff_t;
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dynamic *s;
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public:
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template<class U> struct rebind
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{
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using other = typename dynamic<U>::allocator;
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};
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size_type max_size() const { return s->size; }
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auto address(reference x) const { return &x; }
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auto address(const_reference x) const { return &x; }
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pointer allocate(const size_type &n, const const_pointer &hint = nullptr)
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{
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const uint hintpos(hint? hint - s->buf : -1);
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return s->buf + s->state::allocate(n, hintpos);
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}
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void deallocate(const pointer &p, const size_type &n)
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{
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const uint pos(p - s->buf);
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s->state::deallocate(pos, n);
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}
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template<class U>
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allocator(const typename dynamic<U>::allocator &) noexcept
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:s{reinterpret_cast<dynamic *>(s.s)}
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{}
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allocator(dynamic &s) noexcept
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:s{&s}
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{}
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allocator(allocator &&) = default;
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allocator(const allocator &) = default;
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friend bool operator==(const allocator &a, const allocator &b)
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{
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return &a == &b;
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}
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friend bool operator!=(const allocator &a, const allocator &b)
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{
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return &a == &b;
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}
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};
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template<class T>
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typename ircd::allocator::dynamic<T>::allocator
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ircd::allocator::dynamic<T>::operator()()
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{
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return { *this };
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}
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template<class T>
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ircd::allocator::dynamic<T>::operator
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allocator()
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{
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return { *this };
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}
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/// Allows elements of an STL container to be manually handled by the user.
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///
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/// C library containers usually allow the user to manually construct a node
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/// and then insert it and remove it from the container. With STL containers
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/// we can use devices like allocator::fixed, but what if we don't want to have
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/// a bound on the allocator's size either at compile time or at runtime? What
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/// if we simply want to manually handle the container's elements, like on the
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/// stack, and in different frames, and then manipulate the container -- or
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/// even better and safer: have the elements add and remove themselves while
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/// storing the container's node data too?
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///
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/// This device helps the user achieve that by simply providing a variable
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/// set by the user indicating where the 'next' block of memory is when the
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/// container requests it. Whether the container is requesting memory which
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/// should be fulfilled by that 'next' block must be ensured and asserted by
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/// the user, but this is likely the case.
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///
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template<class T>
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struct ircd::allocator::node
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{
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struct allocator;
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struct monotonic;
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T *next {nullptr};
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node() = default;
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};
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/// The actual template passed to containers for using the allocator.
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///
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/// See the notes for ircd::allocator::fixed::allocator for details.
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///
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template<class T>
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struct ircd::allocator::node<T>::allocator
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{
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using value_type = T;
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using pointer = T *;
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using const_pointer = const T *;
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using reference = T &;
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using const_reference = const T &;
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using size_type = std::size_t;
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using difference_type = std::ptrdiff_t;
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node *s;
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public:
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template<class U> struct rebind
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{
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using other = typename node<U>::allocator;
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};
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size_type max_size() const { return std::numeric_limits<size_t>::max(); }
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auto address(reference x) const { return &x; }
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auto address(const_reference x) const { return &x; }
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template<class U, class... args>
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void construct(U *p, args&&... a)
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{
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new (p) U(std::forward<args>(a)...);
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}
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void construct(pointer p, const_reference val)
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{
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new (p) T(val);
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}
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pointer allocate(const size_type &n, const const_pointer &hint = nullptr)
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{
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assert(n == 1);
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assert(hint == nullptr);
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assert(s->next != nullptr);
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return s->next;
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}
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void deallocate(const pointer &p, const size_type &n)
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{
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assert(n == 1);
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}
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template<class U>
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allocator(const typename node<U>::allocator &s) noexcept
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:s{reinterpret_cast<node *>(s.s)}
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{
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}
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template<class U>
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allocator(const U &s) noexcept
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:s{reinterpret_cast<node *>(s.s)}
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{
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}
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allocator(node &s) noexcept
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:s{&s}
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{
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}
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allocator() = default;
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allocator(allocator &&) noexcept = default;
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allocator(const allocator &) = default;
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friend bool operator==(const allocator &a, const allocator &b)
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{
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return &a == &b;
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}
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friend bool operator!=(const allocator &a, const allocator &b)
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{
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return &a == &b;
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}
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};
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inline void
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ircd::allocator::state::deallocate(const uint &pos,
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const size_type &n)
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{
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for(size_t i(0); i < n; ++i)
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{
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assert(test(pos + i));
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btc(pos + i);
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}
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last = pos;
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}
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inline uint
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ircd::allocator::state::allocate(const size_type &n,
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const uint &hint)
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{
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const auto next(this->next(n));
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if(unlikely(next >= size)) // No block of n was found anywhere (next is past-the-end)
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throw std::bad_alloc();
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for(size_t i(0); i < n; ++i)
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{
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assert(!test(next + i));
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bts(next + i);
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}
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last = next + n;
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return next;
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}
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inline uint
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ircd::allocator::state::next(const size_t &n)
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const
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{
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uint ret(last), rem(n);
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for(; ret < size && rem; ++ret)
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if(test(ret))
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rem = n;
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else
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--rem;
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if(likely(!rem))
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return ret - n;
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for(ret = 0, rem = n; ret < last && rem; ++ret)
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if(test(ret))
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rem = n;
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else
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--rem;
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if(unlikely(rem)) // The allocator should throw std::bad_alloc if !rem
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return size;
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return ret - n;
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}
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