High-radix Division with Approximate Quotient-digit Estimation

High-radix division, developing several quotient bits per clock, is usually limited by the difficulty of generating accurate high-radix quotient digits. This paper describes techniques which allow quotient digits to be inaccurate, but then refine the result. We thereby obtain dividers with slightly reduced performance, but with much simplified logic. For example, a nominal radix-64 divider can generate an average of 4.5 to 5.5 quotient bits per cycle with quite simple digit estimation logic. The paper investigates the technique for radices of 8, 16, 64 and 256, including various qualities of digit estimation, and operation with restricted sets of divisor multiples.