METHOD AND DEVICE FOR CALCULATING RECIPROCAL

摘要

PROBLEM TO BE SOLVED: To provide a method and a device for calculating the reciprocal of normalized decimal part in a floating-point input number D. SOLUTION: An expression for determining the minimum size of a look-up table according to necessary precision and an expression for calculating a look-up entry are provided. The look-up table stores an initial approximation and a correction factor. The initial approximation and the correction factor are designated in address by a number corresponding to the highest position bit of a decimal part and are used for calculating a reciprocal of the initial approximate by a linear interpolation requiring a subtraction and a multiplication. A result of the linear interpolation can be supplied to a Newton-Raphson reiteration device requiring two multiplications and a complement calculation of 2 for each iteration to be able to double the precision of the reciprocal.