Abstract
An efficient format and fast algorithms of basic operations for 4-fold working precision are proposed. The proposed format is an unevaluated sum of four double precision numbers, capable of representing at least 203 bits of mantissa. Hence, it is slightly less accurate than quad-double format proposed by Hida et. al. [1], however presented algorithms based on the format are faster than those algorithms. By numerical experiments it is shown that the proposed algorithms are efficient.
