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480 lines
11 KiB
480 lines
11 KiB
#pragma once
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#include "gp_config.hpp"
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#include "gp/algorithms/modifiers.hpp"
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#include "gp/algorithms/tmp_manip.hpp"
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#include "gp/utils/allocators/dummy.hpp"
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#include "gp/containers/array.hpp"
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#include "gp/containers/buffer.hpp"
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#include "gp/math/integral.hpp"
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#include "gp/utils/allocators/allocator.hpp"
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#include <type_traits>
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namespace gp{
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/**
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* @brief An allocator that uses the buddy algorithm to divide the space into allocatable memory.
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*
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* This is not resilient to memory fragmentation, but the smallest memory unit should always be allocatable unless the memory is actually full.
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*
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* @tparam max_msb The log2 rounded up of the maximum space you expect to address in bytes
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* @tparam align The smallest size of memory you expect the allocator to allocate
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*/
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template<size_t max_msb = 24, size_t align = 8>
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class buddy : public allocator {
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/**
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* @brief an allocation tree node, made into an easily packable struct
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*/
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struct twig {
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bool used : 1;
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bool used_children : 1;
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twig(uint8_t src) noexcept {
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used = 1 & src;
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used_children = 2 & src;
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}
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operator uint8_t() noexcept {
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return 1 * used + 2 * used_children;
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}
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};
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/**
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* @brief a structure to pack 4 twig within
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*/
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struct bundle {
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uint8_t a : 2;
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uint8_t b : 2;
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uint8_t c : 2;
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uint8_t d : 2;
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bundle() noexcept {
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a = 0; b = 0; c = 0; d = 0;
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}
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};
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/**
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* @brief a meta allocator to allocate the memory used and deallocate it later
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*/
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gp::optional<gp::reference_wrapper<allocator>> allocator_v;
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/**
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* @brief The actual buffer where data is stored
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*
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*/
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gp::buffer<char> data;
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const size_t max_depth;
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const size_t twig_explore_length;
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/**
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* @brief The depth of the tree required to allocate
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*/
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static constexpr size_t max_theoric_depth = max_msb - gp::math::msb(align);
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/**
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* @brief The actual number of twigs to support the specified depth
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*/
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static constexpr size_t required_twigs = (1 << (max_theoric_depth + 1)) - 1;
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/**
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* @brief ((max allocatable size - min allocatable size) ** 2 - 1) / 4 twigs in a bundle
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**/
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static constexpr size_t span_size = required_twigs / 4 + (required_twigs % 4 != 0);
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/**
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* @brief The array of twigs (in bundles) aka the metadata
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*/
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gp::array<bundle, span_size> stack;
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/**
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* This code has been manually checked and will always return.
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* If you find a case where it doesn't, please file an issue.
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**/
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#pragma clang diagnostic push
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#pragma clang diagnostic ignored "-Wreturn-type"
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#pragma GCC diagnostic push
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#pragma GCC diagnostic ignored "-Wreturn-type"
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/**
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* @brief Get the value of the twig at the specified index
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*
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* @param idx
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* @return twig A copy of the specified twig
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*/
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twig get_twig(size_t idx) const noexcept {
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auto far = idx / 4;
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auto local = idx % 4;
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switch(local) {
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case 0:
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return stack[far].a;
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case 1:
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return stack[far].b;
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case 2:
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return stack[far].c;
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case 3:
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return stack[far].d;
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}
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}
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#pragma GCC diagnostic pop
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#pragma clang diagnostic pop
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/**
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* @brief Set the twig at the specified index to the value of the heredescribed twig
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*
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* @param idx
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* @param v
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*/
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void set_twig(size_t idx, twig v) noexcept {
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auto far = idx / 4;
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auto local = idx % 4;
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auto& group = stack[far];
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switch(local) {
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case 0:
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group.a = v;
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return;
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case 1:
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group.b = v;
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return;
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case 2:
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group.c = v;
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return;
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case 3:
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group.d = v;
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return;
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}
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}
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/**
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* @brief Deduces the depth to explore to allocate the specified size
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*
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* @param sz
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* @return size_t
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*/
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constexpr size_t size_to_depth(size_t sz) noexcept {
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size_t pow2 = gp::math::msb(sz) - gp::math::msb(align);
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return gp::clamp(
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(size_t)0 ,
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max_depth - pow2,
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max_depth
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);
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}
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/**
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* @brief Deduces the size from the specified depth
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*
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* @param depth
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* @return size_t
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*/
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constexpr size_t depth_to_size(size_t depth) noexcept {
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return 1 << (max_depth - depth + gp::math::msb(align));
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}
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/**
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* @brief Get the left child index from the specified index
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*
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* @param index
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* @return size_t
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*/
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constexpr size_t get_left(size_t index) const noexcept {
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return ((index + 1) << 1) - 1;
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}
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/**
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* @brief Get the right child index from the specified index
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*
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* @param index
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* @return size_t
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*/
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constexpr size_t get_right(size_t index) const noexcept{
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return ((index + 1) << 1);
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}
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/**
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* @brief Recursively applies a function to the children of a given node
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*
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* @param index the starting node
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* @param func the function to apply downwards
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*/
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template<typename function>
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void all_under(size_t index, function func) {
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size_t left = get_left(index);
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size_t right = get_right(index);
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all_under(left, func);
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all_under(right, func);
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func(left);
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func(right);
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}
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/**
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* @brief Recursively applies a function to the chain of parents of the given node
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*
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* @param index the starting node
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* @param func the function to apply upwards
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*/
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template<typename function>
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void all_over(size_t index, function func) {
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if(index != 0) {
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size_t parent = ((index + 1) >> 1) - 1;
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func(parent);
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if(parent != 0)
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all_over(parent, func);
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}
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}
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/**
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* @brief Recursively checks if any child matches a given predicate
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*
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* @param index The parent
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* @param func The predicate
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* @return true if the predicate matched once
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* @return false if the predicate never matched
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*/
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template<typename function>
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bool is_any_child(size_t index, function func) const {
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size_t left = get_left(index);
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size_t right = get_right(index);
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if(left < twig_explore_length && right < twig_explore_length) {
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if(func(left)) return true;
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if(func(right)) return true;
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if(is_any_child(left, func)) return true;
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if(is_any_child(right, func)) return true;
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}
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return false;
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}
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/**
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* @brief a constant used to specify that no twig has been found
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*/
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static constexpr size_t no_twig = -1;
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/**
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* @brief Finds a twig that represent free memory
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*
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* It's free real estate!
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*
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* @param depth the depth to allocate
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* @param root the root to look from
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* @param explored the current depth we sit at
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* @return size_t
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*/
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size_t find_free_twig(size_t depth, size_t root = 0, size_t explored = 0) const {
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auto v = get_twig(root);
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if(depth == explored) {
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if(v.used || v.used_children)
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{
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return no_twig;
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} else {
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return root;
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}
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} else {
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if(v.used)
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{
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return no_twig;
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}
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++explored;
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auto ret = find_free_twig(depth, get_right(root), explored);
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if(ret != no_twig)
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{
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return ret;
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}
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ret = find_free_twig(depth, get_left(root), explored);
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if(ret != no_twig)
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{
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return ret;
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}
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}
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return no_twig;
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}
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/**
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* @brief Recursively looks for the highest filled nodewith the given offset
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*
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* @param offset The offset to look for
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* @param root the root to look from
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* @param explored the explored depth
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* @return size_t
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*/
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size_t find_used_twig(size_t offset, size_t root = 0, size_t explored = 0) {
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auto v = get_twig(root);
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if(v.used && offset == 0)
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{
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return root;
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}
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++explored;
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if(explored > max_depth) return no_twig;
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size_t cut = (1 << (max_depth + gp::math::log2(align))) >> explored;
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if(offset >= cut)
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{
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return find_used_twig(offset-cut, get_right(root), explored);
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} else {
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return find_used_twig(offset, get_left(root), explored);
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}
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}
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static bool empty_node(const buddy* me, size_t node) {
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gp_config::assertion(node < me->twig_explore_length, "bad emptyness test");
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auto p = me->get_twig(node);
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return !(
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p.used | p.used_children
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);
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}
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public:
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/**
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* @brief Construct a new empty buddy object
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*/
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buddy()
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: data(gp::buffer<char>(nullptr,nullptr))
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, max_depth(0)
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, twig_explore_length(1 << max_depth)
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{}
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/**
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* @brief Construct a new buddy object from another allocator
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*
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* @param sz the size to allocate
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* @param allocator_p the source of the allocated memory
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*/
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buddy(size_t sz, allocator& allocator_p)
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: allocator_v(allocator_p)
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, data(nullptr,nullptr)
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, max_depth(gp::math::msb(sz)-gp::math::msb(align))
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, twig_explore_length(1 << max_depth)
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{
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if(sz!=0 && (sz & (sz - 1)) == 0)
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{
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auto v=allocator_v.value().get().allocate(sz);
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if(v!=nullptr)
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{
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if((reinterpret_cast<intptr_t>(v) % align) ==0)
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{
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data=gp::buffer<char>(reinterpret_cast<char*>(v),reinterpret_cast<char*>(v)+sz);
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}
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else
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{
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allocator_v.value().get().deallocate(v);
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}
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}
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}
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}
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/**
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* @brief Construct a new buddy object from a memory location
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*
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* @param pos the location of the memory to manage
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* @param sz the size of the span to manage
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*/
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buddy(char* pos, size_t sz)
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: data(pos,pos+sz)
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, max_depth(gp::math::msb(sz)-gp::math::msb(align))
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, twig_explore_length(1 << max_depth)
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{
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}
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/**
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* @brief Allocates memory
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*
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* @param sz The size of memory to allocate
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* @return void* the allocated memory OR nullptr
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*/
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virtual void* allocate(size_t sz)
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{
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auto depth = size_to_depth(sz);
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auto index = find_free_twig(depth);
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if(index == no_twig)
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{
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return nullptr;
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}
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auto pot = reinterpret_cast<char*>(
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(index - (1 << depth) + 1)*depth_to_size(depth)
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+ reinterpret_cast<intptr_t>(&*data.begin())
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);
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if(!data.contains(pot)) {
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return nullptr;
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}
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all_over(index, [&](size_t idx){
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auto t = get_twig(idx);
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t.used_children = true;
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set_twig(idx, t);
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});
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auto t = get_twig(index);
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t.used = true;
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set_twig(index, t);
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return pot;
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}
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/**
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* @brief Tries to reallocate (UNIMPLEMENTED)
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*
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* @return false
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*/
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virtual bool try_reallocate(void*, size_t) {
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return false;
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}
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/**
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* @brief Tries to deallocate the given memory
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*
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* @param ptr the pointer to the memory to deallocate
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* @return true if everything went fine
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* @return false if deallocation failed
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*/
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virtual bool deallocate(void* ptr)
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{
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if(data.contains((char*)ptr))
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{
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size_t integral_offset = reinterpret_cast<intptr_t>(ptr) - reinterpret_cast<intptr_t>(&*data.begin());
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auto index = find_used_twig(integral_offset);
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if(index == no_twig)
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{
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return false;
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}
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twig v = get_twig(index);
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v.used = false;
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v.used_children = false;
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set_twig(index, v);
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all_over(index, [&](size_t idx){
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auto l = get_twig(get_left(idx));
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auto r = get_twig(get_right(idx));
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// And now for the tricky bit:
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// Sets the "used_children" bit if any of the collected twigs has a bit set
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set_twig(idx, 2*(l.used | l.used_children | r.used | r.used_children));
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});
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return true;
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}
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return false;
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}
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/**
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* @brief Checks if anything is still allocated in
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*
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* @return true if the allocator is completely empty
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* @return false if anything is still allocated in there
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*/
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bool empty() const noexcept {
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const buddy* addr = (buddy*)this;
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const auto prepred = not_fn(&buddy::empty_node);
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const auto pred = bind_front(prepred, addr);
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return empty_node(addr, 0) && !is_any_child(0, pred);
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}
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/**
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* @brief Destroy the buddy object, will wrink out the space if it was created with an allocator
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*/
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virtual ~buddy()
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{
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if(allocator_v.has_value())
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{
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allocator_v.value().get().deallocate(data.begin().data);
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}
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}
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};
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}
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