DATA PROCESSOR, DATA PROCESSING METHOD AND PROCESSING PROGRAM

PROBLEM TO BE SOLVED: To obtain a value near one for an arccosine function acos(x) with high accuracy. SOLUTION: A data processor 1 has a data processing unit 20. The data processing unit that executes a processing control program performs polynomial calculations of F(1-x) using Horner's method when calculating the value of the function acos(x) with respect to an input x using a polynomial F(x) and a constant C in acos(x)=F(1-x)*sqrt(C*(1-x)) in accordance with the processing control program. The final addition thereof is reserved and the value cst of a constant term and the value α of an addition term in the polynomial F(x) are stored separately. Further, the sqrt(C*(1-x)) is stored as it it separated into the value sq1 of an added term and the value of the addition term using Newton's method. Using the whole of, or part of the head of, an expansion cst*sq1+α*sq1+cst* +α* of (cst+α)*(sq1+ ), the value of the function acos(x) with respect to the input x is computed. COPYRIGHT: (C)2006,JPO&NCIPI