| 摘要 |
PURPOSE: To provide an improved device and method for calculating the inverse number and the square root. CONSTITUTION: An initial value approximation formula with high accuracy is calculated by using a quadratic polynomial, and the coefficients are stored in an ROM. Address designation is performed to the ROM by using the most significant bit of an operand to select the coefficient, and a different operand range is given to a different coefficient. Operand bits at the residual lower side are used for calculation and the coefficient value indicates the bit used for address designation. As a result, single precision can be obtained. The result, of the polynomial is used as the first approximation formula of a Newton- Raphson successive solution in double precision. A multiplier can calculate once two values with low precision by a division array mode for quickening the calculation of the polynomial. The size of the coefficients is adapted so as to calculate a proper result with high precision for each element of Ax<2> +Bx+C. In this case, each value of the coefficients A, B, and C must be stored for 1/x approximation formula and 1/(x)<1/2> approximation formula. |
