OVFLSIZE
_DIAGASSERT(FREESPACE(tp) >= OVFLSIZE);
temp = free_space - OVFLSIZE;
temp = free_space + OVFLSIZE;
_DIAGASSERT(temp >= OVFLSIZE);
sp[ndx + 3] = (uint16_t)(temp - OVFLSIZE);
(PAIRSIZE((K),(D)) + OVFLSIZE) <= FREESPACE((P)))