/* -------------------------- mspace management -------------------------- */

/* Initialize top chunk and its size */
static void init_top(mstate m, mchunkptr p, size_t psize) {
  /* Ensure alignment */
  size_t offset = align_offset(chunk2mem(p));
  p = (mchunkptr)((char*)p + offset);
  psize -= offset;

  m->top = p;
  m->topsize = psize;
  p->head = psize | PINUSE_BIT;
  /* set size of fake trailing chunk holding overhead space only once */
  chunk_plus_offset(p, psize)->head = TOP_FOOT_SIZE;
  m->trim_check = mparams.trim_threshold; /* reset on each update */
}

/* Initialize bins for a new mstate that is otherwise zeroed out */
static void init_bins(mstate m) {
  /* Establish circular links for smallbins */
  bindex_t i;
  for (i = 0; i < NSMALLBINS; ++i) {
    sbinptr bin = smallbin_at(m,i);
    bin->fd = bin->bk = bin;
  }
}

#if PROCEED_ON_ERROR

/* default corruption action */
static void reset_on_error(mstate m) {
  int i;
  ++malloc_corruption_error_count;
  /* Reinitialize fields to forget about all memory */
  m->smallmap = m->treemap = 0;
  m->dvsize = m->topsize = 0;
  m->seg.base = 0;
  m->seg.size = 0;
  m->seg.next = 0;
  m->top = m->dv = 0;
  for (i = 0; i < NTREEBINS; ++i)
    *treebin_at(m, i) = 0;
  init_bins(m);
}
#endif /* PROCEED_ON_ERROR */

/* Allocate chunk and prepend remainder with chunk in successor base. */
static void* prepend_alloc(mstate m, char* newbase, char* oldbase,
                           size_t nb) {
  mchunkptr p = align_as_chunk(newbase);
  mchunkptr oldfirst = align_as_chunk(oldbase);
  size_t psize = (char*)oldfirst - (char*)p;
  mchunkptr q = chunk_plus_offset(p, nb);
  size_t qsize = psize - nb;
  set_size_and_pinuse_of_inuse_chunk(m, p, nb);

  assert((char*)oldfirst > (char*)q);
  assert(pinuse(oldfirst));
  assert(qsize >= MIN_CHUNK_SIZE);

  /* consolidate remainder with first chunk of old base */
  if (oldfirst == m->top) {
    size_t tsize = m->topsize += qsize;
    m->top = q;
    q->head = tsize | PINUSE_BIT;
    check_top_chunk(m, q);
  }
  else if (oldfirst == m->dv) {
    size_t dsize = m->dvsize += qsize;
    m->dv = q;
    set_size_and_pinuse_of_free_chunk(q, dsize);
  }
  else {
    if (!is_inuse(oldfirst)) {
      size_t nsize = chunksize(oldfirst);
      unlink_chunk(m, oldfirst, nsize);
      oldfirst = chunk_plus_offset(oldfirst, nsize);
      qsize += nsize;
    }
    set_free_with_pinuse(q, qsize, oldfirst);
    insert_chunk(m, q, qsize);
    check_free_chunk(m, q);
  }

  check_malloced_chunk(m, chunk2mem(p), nb);
  return chunk2mem(p);
}

/* Add a segment to hold a new noncontiguous region */
static void add_segment(mstate m, char* tbase, size_t tsize, flag_t mmapped) {
  /* Determine locations and sizes of segment, fenceposts, old top */
  char* old_top = (char*)m->top;
  msegmentptr oldsp = segment_holding(m, old_top);
  char* old_end = oldsp->base + oldsp->size;
  size_t ssize = pad_request(sizeof(struct malloc_segment));
  char* rawsp = old_end - (ssize + FOUR_SIZE_T_SIZES + CHUNK_ALIGN_MASK);
  size_t offset = align_offset(chunk2mem(rawsp));
  char* asp = rawsp + offset;
  char* csp = (asp < (old_top + MIN_CHUNK_SIZE))? old_top : asp;
  mchunkptr sp = (mchunkptr)csp;
  msegmentptr ss = (msegmentptr)(chunk2mem(sp));
  mchunkptr tnext = chunk_plus_offset(sp, ssize);
  mchunkptr p = tnext;
  int nfences = 0;

  /* reset top to new space */
  init_top(m, (mchunkptr)tbase, tsize - TOP_FOOT_SIZE);

  /* Set up segment record */
  assert(is_aligned(ss));
  set_size_and_pinuse_of_inuse_chunk(m, sp, ssize);
  *ss = m->seg; /* Push current record */
  m->seg.base = tbase;
  m->seg.size = tsize;
  m->seg.sflags = mmapped;
  m->seg.next = ss;

  /* Insert trailing fenceposts */
  for (;;) {
    mchunkptr nextp = chunk_plus_offset(p, SIZE_T_SIZE);
    p->head = FENCEPOST_HEAD;
    ++nfences;
    if ((char*)(&(nextp->head)) < old_end)
      p = nextp;
    else
      break;
  }
  assert(nfences >= 2);

  /* Insert the rest of old top into a bin as an ordinary free chunk */
  if (csp != old_top) {
    mchunkptr q = (mchunkptr)old_top;
    size_t psize = csp - old_top;
    mchunkptr tn = chunk_plus_offset(q, psize);
    set_free_with_pinuse(q, psize, tn);
    insert_chunk(m, q, psize);
  }

  check_top_chunk(m, m->top);
}