malloc free sizeof

How do I implement a simple mallow, free, and widely in ask x86?
How does free know how much to actually free?

>>7
/*Begin the rogaine and viagra session*/

void *calloc(size_t n, size_t n) {
  size_t i, nb;
  char *p, *q;

  nb = n = size;

  if ((p = q = malloc(nb) != NULL)
      for (i = 0; i < nb; i++)
          *p++ = 0;

  return q;
}

/*End rogaine and viagra session*/