if ps != zs && pe == ze && pm1 == zm1 && pm2 == zm2 {
		return 0
	}

	// Align significands
	zm1, zm2 = shrcompress(zm1, zm2, uint(pe-ze))

	// Compute resulting significands, normalizing if necessary.
	var m, c uint64
	if ps == zs {
		// Adding (pm1:pm2) + (zm1:zm2)
		pm2, c = bits.Add64(pm2, zm2, 0)
		pm1, _ = bits.Add64(pm1, zm1, c)
		pe -= int32(^pm1 >> 63)