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#include <string.h>
#include <stdlib.h>
#include <sys/mman.h>
#include "config.h"
struct heap_node
{
size_t size;
union
{
struct
{
struct heap_node *prev;
struct heap_node *next;
};
struct
{
char block;
};
};
};
struct heap_head
{
size_t allocated_size;
size_t maximum_size;
size_t minimum_alloc;
struct heap_node *root;
};
struct heap_head *heap;
void *allocate_superblock(void)
{
return mmap(nullptr, HEAP_SEGMENT_SIZE, 0, 0, -1, 0);
}
static struct heap_node *try_create_heap()
{
if (heap != nullptr) return heap->root;
char *superblock = allocate_superblock();
heap = (struct heap_head *)superblock;
heap->root = (struct heap_node *)(superblock + sizeof(struct heap_head));
heap->allocated_size = HEAP_SEGMENT_SIZE;
heap->maximum_size = HEAP_MAX_SIZE;
heap->minimum_alloc = sizeof(heap->root);
heap->root->next = nullptr;
heap->root->prev = nullptr;
heap->root->size = HEAP_SEGMENT_SIZE - sizeof(superblock) - sizeof(heap->root->size);
return heap->root;
}
static struct heap_node *try_grow_heap(struct heap_node *prev)
{
if (heap->allocated_size >= heap->maximum_size)
{
return nullptr;
}
struct heap_node *node = allocate_superblock();
if (node == nullptr)
{
return nullptr;
}
node->size = HEAP_SEGMENT_SIZE - sizeof(node->size);
node->prev = prev;
prev->next = node;
return node;
}
static inline size_t get_node_size(size_t size)
{
return size + sizeof(size);
}
static inline bool can_divide_node(struct heap_node *parent)
{
return parent->size <= heap->minimum_alloc + sizeof(struct heap_node);
}
static inline void *new_node_address(struct heap_node *parent, size_t size)
{
return &parent->block + parent->size - get_node_size(size);
}
static inline struct heap_node *divide_node(struct heap_node *parent, size_t size)
{
struct heap_node *child = new_node_address(parent, size);
parent->size -= get_node_size(size);
child->size = size;
return child;
}
static inline struct heap_node *try_divide_node(struct heap_node *node, size_t size)
{
return can_divide_node(node) ? divide_node(node, size) : node;
}
static inline struct heap_node *allocate_node(size_t size)
{
struct heap_node *node = try_create_heap();
while(node != nullptr)
{
if (node->size > size)
{
break;
}
node = node->next
? node->next
: try_grow_heap(node);
}
return node;
}
void *malloc(size_t size)
{
// TODO: min(heap->minimum_alloc, size);
size = size >= heap->minimum_alloc
? size
: heap->minimum_alloc;
struct heap_node *node = try_divide_node(allocate_node(size), size);
return node != nullptr
? &node->block
: nullptr;
}
void *calloc(size_t count, size_t size)
{
void *block = malloc(count * size);
if (block != nullptr)
{
memset(block, 0, count * size);
}
return block;
}
static inline struct heap_node *block_to_node(char *block)
{
return (struct heap_node *)(block - sizeof(size_t));
}
void free(void *block)
{
// TODO: insertion sort by address of node
// TODO: coalesce adjacent nodes
if (block == nullptr)
{
return;
}
struct heap_node *node = block_to_node(block);
node->prev = nullptr;
node->next = heap->root;
heap->root = node;
if (node->next != nullptr)
{
node->next->prev = node;
}
}
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