Function internal_memalign

dlmalloc/dlmalloc.c:4154–4237

/* --------------------------- memalign support -------------------------- */

static void* internal_memalign(mstate m, size_t alignment, size_t bytes) {
  if (alignment <= MALLOC_ALIGNMENT)    /* Can just use malloc */
    return internal_malloc(m, bytes);
  if (alignment <  MIN_CHUNK_SIZE) /* must be at least a minimum chunk size */
    alignment = MIN_CHUNK_SIZE;
  if ((alignment & (alignment-SIZE_T_ONE)) != 0) {/* Ensure a power of 2 */
    size_t a = MALLOC_ALIGNMENT << 1;
    while (a < alignment) a <<= 1;
    alignment = a;
  }
  
  if (bytes >= MAX_REQUEST - alignment) {
    if (m != 0)  { /* Test isn't needed but avoids compiler warning */
      MALLOC_FAILURE_ACTION;
    }
  }
  else {
    size_t nb = request2size(bytes);
    size_t req = nb + alignment + MIN_CHUNK_SIZE - CHUNK_OVERHEAD;
    char* mem = internal_malloc(m, req);
    if (mem != 0) {
      void* leader = 0;
      void* trailer = 0;
      mchunkptr p = mem2chunk(mem);

      if (PREACTION(m)) return 0;
      if ((((size_t)(mem)) % alignment) != 0) { /* misaligned */
        /*
          Find an aligned spot inside chunk.  Since we need to give
          back leading space in a chunk of at least MIN_CHUNK_SIZE, if
          the first calculation places us at a spot with less than
          MIN_CHUNK_SIZE leader, we can move to the next aligned spot.
          We've allocated enough total room so that this is always
          possible.
        */
        char* br = (char*)mem2chunk((size_t)(((size_t)(mem +
                                                       alignment -
                                                       SIZE_T_ONE)) &
                                             -alignment));
        char* pos = ((size_t)(br - (char*)(p)) >= MIN_CHUNK_SIZE)?
          br : br+alignment;
        mchunkptr newp = (mchunkptr)pos;
        size_t leadsize = pos - (char*)(p);
        size_t newsize = chunksize(p) - leadsize;

        if (is_mmapped(p)) { /* For mmapped chunks, just adjust offset */
          newp->prev_foot = p->prev_foot + leadsize;
          newp->head = (newsize|CINUSE_BIT);
        }
        else { /* Otherwise, give back leader, use the rest */
          set_inuse(m, newp, newsize);
          set_inuse(m, p, leadsize);
          leader = chunk2mem(p);
        }
        p = newp;
      }

      /* Give back spare room at the end */