return xmcalloc (NULL, number, size);
void *mem;   if (number == 0 || size == 0) { number = 1; size = 1; }  mem = calloc (number, size);		 if (mem == NULL) nomem (number * size);  return mem;
xcalloc (size_t number, size_t size){  return xmcalloc (NULL, number, size);}