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#if CHAPTER >= 8
// 
// heap.c -- Defines functions and structures for the kernel heap.
//           Written for JamesM's kernel development tutorials.
//

#include "heap.h"
#include "pmm.h"
#include "vmm.h"

static void alloc_chunk (uint32_t start, uint32_t len);
static void free_chunk (header_t *chunk);
static void split_chunk (header_t *chunk, uint32_t len);
static void glue_chunk (header_t *chunk);

uint32_t heap_max = HEAP_START;
header_t *heap_first = 0;

void init_heap ()
{
}

void *kmalloc (uint32_t l)
{
  l += sizeof (header_t);

  header_t *cur_header = heap_first, *prev_header = 0;
  while (cur_header)
  {
    if (cur_header->allocated == 0 && cur_header->length >= l)
    {
      split_chunk (cur_header, l);
      cur_header->allocated = 1;
      return (void*) ((uint32_t)cur_header + sizeof (header_t));
    }
    prev_header = cur_header;
    cur_header = cur_header->next;
  }

  uint32_t chunk_start;
  if (prev_header)
    chunk_start = (uint32_t)prev_header + prev_header->length;
  else
  {
    chunk_start = HEAP_START;
    heap_first = (header_t *)chunk_start;
  }

  alloc_chunk (chunk_start, l);
  cur_header = (header_t *)chunk_start;
  cur_header->prev = prev_header;
  cur_header->next = 0;
  cur_header->allocated = 1;
  cur_header->length = l;

  prev_header->next = cur_header;

  return (void*) (chunk_start + sizeof (header_t));
}

void kfree (void *p)
{
  header_t *header = (header_t*)((uint32_t)p - sizeof(header_t));
  header->allocated = 0;

  glue_chunk (header);
}

void alloc_chunk (uint32_t start, uint32_t len)
{
  while (start + len > heap_max)
  {
    uint32_t page = pmm_alloc_page ();
    map (heap_max, page, PAGE_PRESENT | PAGE_WRITE);
    heap_max += 0x1000;
  }
}

void free_chunk (header_t *chunk)
{
  chunk->prev->next = 0;

  if (chunk->prev == 0)
  heap_first = 0;

  // While the heap max can contract by a page and still be greater than the chunk address...
  while ( (heap_max-0x1000) >= (uint32_t)chunk )
  {
    heap_max -= 0x1000;
    uint32_t page;
    get_mapping (heap_max, &page);
    pmm_free_page (page);
    unmap (heap_max);
  }
}

void split_chunk (header_t *chunk, uint32_t len)
{
  // In order to split a chunk, once we split we need to know that there will be enough
  // space in the new chunk to store the chunk header, otherwise it just isn't worthwhile.
  if (chunk->length - len > sizeof (header_t))
  {
    header_t *newchunk = (header_t *) ((uint32_t)chunk + chunk->length);
    newchunk->prev = chunk;
    newchunk->next = 0;
    newchunk->allocated = 0;
    newchunk->length = chunk->length - len;

    chunk->next = newchunk;
    chunk->length = len;
  }
}

void glue_chunk (header_t *chunk)
{
  if (chunk->next && chunk->next->allocated == 0)
  {
    chunk->length = chunk->length + chunk->next->length;
    chunk->next->next->prev = chunk;
    chunk->next = chunk->next->next;
  }

  if (chunk->prev && chunk->prev->allocated == 0)
  {
    chunk->prev->length = chunk->prev->length + chunk->length;
    chunk->prev->next = chunk->next;
    chunk->next->prev = chunk->prev;
    chunk = chunk->prev;
  }

  if (chunk->next == 0)
    free_chunk (chunk);
}
#endif // CHAPTER >= 8