#include "libimagequant.h"
#include "mempool.h"
#include <stdlib.h>
#include <stdint.h>
#include <assert.h>

#define ALIGN_MASK 15UL
#define MEMPOOL_RESERVED ((sizeof(struct mempool)+ALIGN_MASK) & ~ALIGN_MASK)

struct mempool
{
  unsigned int used, size;
  void *(*malloc) (size_t);
  void (*free) (void *);
  struct mempool *next;
};
LIQ_PRIVATE void *
mempool_create (mempool * mptr, const unsigned int size, unsigned int max_size,
    void *(*malloc) (size_t), void (*free) (void *))
{
  mempool old;
  uintptr_t mptr_used_start;

  if (*mptr && ((*mptr)->used + size) <= (*mptr)->size) {
    unsigned int prevused = (*mptr)->used;
    (*mptr)->used += (size + 15UL) & ~0xFUL;
    return ((char *) (*mptr)) + prevused;
  }

  old = *mptr;
  if (!max_size)
    max_size = (1 << 17);
  max_size = size + ALIGN_MASK > max_size ? size + ALIGN_MASK : max_size;

  *mptr = malloc (MEMPOOL_RESERVED + max_size);
  if (!*mptr)
    return NULL;
  **mptr = (struct mempool) {
    .malloc = malloc,.free = free,.size = MEMPOOL_RESERVED + max_size,.used =
        sizeof (struct mempool),.next = old,
  };
  mptr_used_start = (uintptr_t) (*mptr) + (*mptr)->used;
  (*mptr)->used += (ALIGN_MASK + 1 - (mptr_used_start & ALIGN_MASK)) & ALIGN_MASK;      // reserve bytes required to make subsequent allocations aligned
  assert (!(((uintptr_t) (*mptr) + (*mptr)->used) & ALIGN_MASK));

  return mempool_alloc (mptr, size, size);
}

LIQ_PRIVATE void *
mempool_alloc (mempool * mptr, unsigned int size, unsigned int max_size)
{
  if (((*mptr)->used + size) <= (*mptr)->size) {
    unsigned int prevused = (*mptr)->used;
    (*mptr)->used += (size + ALIGN_MASK) & ~ALIGN_MASK;
    return ((char *) (*mptr)) + prevused;
  }

  return mempool_create (mptr, size, max_size, (*mptr)->malloc, (*mptr)->free);
}

LIQ_PRIVATE void
mempool_destroy (mempool m)
{
  while (m) {
    mempool next = m->next;
    m->free (m);
    m = next;
  }
}