Carry generator based on XOR, and conditional select adder using the carry generator, and method therefor

A carry generator which generates a carry of two n-bit input data units X0-Xn−1, and Y0-Yn−1, the carry generator comprising one or more first sub-carry generating units, each of which comprises:

• a first input unit which receives data based on input data X2i−1 and Y2i−1;
• a second input unit which receives initial carry data;
• and
• a selection unit which receives the result of performing an XOR operation on the input data X2i−1 and Y2i−1, wherein according to the XOR result, the first sub-carry generating unit selects either data based on input data X2i−1 and Y2i−1 input to the first input unit, or the initial carry data input to the second input unit, and outputs the selected data.

A conditional select adder which comprises a plurality of addition modules, each of which has a carry generating unit which generates the carry of two n-bit input data units X0-Xn−1, and Y0-Yn−1, and a sum generating unit which generates the sum of the input values;

• and a block carry generating unit which in response to the carries generated by the addition modules, determines the presence of a carry of each of the addition modules, and feeds the result back to the next stage addition module, wherein each carry generating unit comprises:
• one or more first sub-carry generating units, each of which comprises a first input unit which receives data based on input data X2i−1 and Y2i−1;
• a second input unit which receives initial carry data;
• and a first selection unit which receives the result of performing an XOR operation on the input data X2i−1 and Y2i−1, wherein according to the XOR result input to the selection unit, the first sub-carry generating unit selects either data based on the input data X2i−1 and Y2i−1 input to the first input unit, or the initial carry data input to the second input unit, and outputs the selected data;
• one or more second sub-carry generating units, each of which comprises a first input unit which receives initial carry data;
• a second input unit which receives data based on input data X2i−1 and Y2i−1;
• and a second selection unit which receives the result of performing an XNOR operation on the input data X2i−1 and Y2i−1, wherein according to the XNOR result input to the selection unit, the second sub-carry generating unit selects either the initial carry data input to the first input unit or the data based on input data X2i−1 and Y2i−1 input to the second input unit, and outputs the selected data;
• and
• one or more carry selection units, each of which has two input units to which the outputs of the first sub-carry generating unit and the second sub-carry generating unit are input, and a third selection unit to which a predetermined selection signal is input, wherein according to the selection signal input to the selection unit, one of the values input to the input units is output.

A carry generating method which is used in an addition apparatus and generates a carry of two n-bit input data units X0-Xn−1 and Y0-Yn−1, comprising:

• (a) calculating predetermined data based on input data X2i−1 and Y2i−1;
• (b) calculating first initial carry data of the input data X2i−1 and Y2i−1;
• (c) calculating the result of performing an XOR operation on input data X2i−1 and Y2i−1;
• and
• (d) according to the calculated result of performing an XOR operation on the input data X2i−1 and Y2i−1, selecting either the data based on input data X2i−1 and Y2i−1, or the first initial carry data, and outputting the selected data as a first carry.