Patent ID: 8156171

Claim:
A digital logic circuit for calculating an estimate of reciprocal square root of an input value, said digital logic circuit comprising: a calculator unit for calculating an initial value from the input value, said calculator unit comprising: circuitry that rounds the input value to the nearest number of the form 2 J , where J is an integer; circuitry that derives an integer J′ from J by, when J is odd, adding ‘1’ to J, and, when J is even, setting J′ equal to J, and circuitry that calculates 2 −J″/2 as said initial value; a multiply-and-shift unit having two inputs and an output; an add unit having two inputs, one of said two inputs of said add unit being an output of said multiply-and-shift unit; first feedback-selection circuitry that selects, as one input of said multiply-and-shift unit, one of (a) said initial value, and (b) an output of said multiply-and-shift unit; and second feedback-selection circuitry that selects, as another input of said multiply-and-shift unit, one of (a) said input value, b) an output of said multiply-and-shift unit, and (c) an output of said add unit.