Patent ID: 6850960

Claim:
An inverse calculating apparatus comprising: input means for storing an input x in storage means; storage means for staring integers n and i and 2 n -bit integer x, y, a and b, where said integers n and i are equal to or greater than 1; first b-initializing means for calculating [x/2] using said x stored in said storage means and storing the calculation result as said b in said storage means, where [x] is the maximum integer not exceeding x; a-initializing means for storing the least significant bit of said b as a in said storage means; second b-initializing means for calculating [(ax+b)/2] using said a, x and b stored in said storage means and updating said b stored in said storage means with the calculation result; y-initializing means for acquiring low-order two bits of said x stored in said storage means and storing them as said y in said storage means; i-initializing means for setting said i in said storage means to 1; a-updating for calculating −by using said b and y stored in said storage means and updating said a stored in said storage means with the calculation result; b-updating means for calculating [(b+ax)/(2^(2 i ))] using said a, b, x and i stored in said storage means and updating said b stored in said storage means with the calculation result, where p^q represents the q-th power of p; y-updating means for calculating y+ax2^(2 i ) using said a, y and i stored in said storage means and updating said y stored in said storage means with the calculation result; i-updating means for updating said i stored in said storage means to i+1; control means for reading out said i and n from said storage means and actuating said a-updating means, said b-updating means, said y-updating means and said i-updating means one after another until i=n; and output means for outputting said y stored in said storage means.