Small multiplier after initial approximation for operations with increasing precision

摘要

An apparatus comprises an initial approximation circuit (e.g. Look-Up Table) for providing an initial approximation of an output value; a limited-precision multiplier circuit, which receives the initial approximation circuit and multiplies it with another value; and a full-precision multiplier circuit, which receives an output from the limited-precision circuit, and multiplies it with another value. The number of cycles taken to perform the full-precision multiplication is greater than or equal to the time taken to perform both the initial approximation and the limited-precision multiplication. The full-precision multiplier circuitry preferable performs a double-precision multiplication between two mantissas. The apparatus preferably provides a value for a dividend by a divisor; and the initial approximation is a reciprocal of the divisor. The apparatus may provide a value for a square root, with the initial approximation being of a reciprocal of the square root. The invention is intended for use in an iterative refinement approach (e.g. Newton-Raphson).