Opposite trigonometric function arithmetical unit

摘要

PURPOSE:To operate an inverse trigonometric function arctan(chi) at high speed by inputting a value 1/H2+1 and a low-order digit L in a memory to a multiplier, and adding the output value of the multiplier on a value arctan(H) by an adder. CONSTITUTION:The value (chi) is divided into a high-order digit H and the low- order digit L by every (n) digits. Then, in equation I, the arctan(chi) can be obtained by one time of multiplication and that of addition by preparing a table ROM 12 which inputs H and outputs the value arctan(H) and the value 1/H2+1. Since it is H1 and L2-n, (n) digits are enough for the arithmetic accuracy of a second item in equation I. To obtain accuracy of 2n digits in the arctan (chi), it is necessary to provide an arctan(H) table of 2n digits X2n words, a 1/H2+1 table of (n)digits X 2 words, and the multiplier 14 which performs the multiplication of the output(n) digits of the 1/H2+1 table by (n) digits of L, and the adder 16 which adds the high-order (n) digits of a multiplication result on the output 2n digits of the arctan(H) table. In such a way, it is possible to operate the arctan(chi) at high speed.