An apparatus uses a sticky digit in rounding an interim solution Yr into a final approximate solution Ye for an infinite precise solution Y, determined by a function F according to Y=F(X) with respect to digital data X. The apparatus includes a partial product generator receiving a multiplicand and a multiplier, at least one of which represents an interim solution Yr, for generating a plurality of partial products; a sign inversion generator for generating a sign inversion value, expressed in the same format as the partial products, from at least a lower part of a subtrahend to enable place matching, where the subtrahend represents the digital data X; an adder for adding the partial products and the sign inversion value; a detector which, in response to the addition result, detects whether the subtrahend or a product of the multiplicand and multiplier is greater; and a sticky digit generator for generating the sticky digit in response to the detection result.