typedef union { char irrelevant[ALIGNMENT]; double d; } aligned;
  static aligned realspace[SPACE / ALIGNMENT];
  #define space ((char *) realspace)
  static unsigned int avail = SPACE; /* multiple of ALIGNMENT; 0<=avail<=SPACE */

  char *alloc(n)
  unsigned int n;
  {
    n = ALIGNMENT + n - (n & (ALIGNMENT - 1)); /* XXX: could overflow */
    if (n <= avail) {
      avail -= n;
      return space + avail;
    }
    return malloc(n);
  }

  void alloc_free(x)
  char *x;
  {
    if (x >= space && x < space + SPACE) {
      return; /* XXX: assuming that pointers are flat */
    }
    free(x);
  }