Bidirectional Exact Integer Division

Division of integers is calledexactif the remainder is zero. We show that the high-order part and the low-order part of the exact quotient can be computed independently from each other. A sequential implementation of this algorithm is up to twice as fast as ordinary exact division and four times as fast as the general classical division algorithm if the dividend is twice as long as the divisor. A shared-memory parallel implementation on two processors gains another factor of two in speed.