1. A method for performing both error-check and exact-check operations for a Newton-Raphson divide or square-root computation, comprising: in an arithmetic unit in a computing device, performing Newton-Raphson iterations followed by a multiply for a divide or a square-root operation to produce a result, that includes one or more additional bits of accuracy beyond a desired accuracy for the result; rounding the result to the desired accuracy to produce a rounded result t; and analyzing the additional bits of accuracy to determine whether t is correct and whether t is exact; wherein, if there are k additional bits and n=2 k , analyzing the additional bits involves using n to compare to a value j contained in the additional bits.