4-2 compressor circuit and voltage holding circuit for use in 4-2 compressor circuit

A 4-2 compressor circuit calculates the sum of first through fourth inputs and a carry input applied thereto and for furnishing the summation result and first and second carries generated during the calculation of the summation. An input value converting unit inverts the third and fourth inputs only if the third input is logic 0 and the fourth input is logic 1. A summation unit calculates the logical exclusive OR of any two of the first through fourth inputs and the carry input applied to the 4-2 compressor circuit, the logical exclusive OR of any two of the first logical exclusive OR and the remaining three inputs, the logical exclusive OR of any two of the second logical exclusive OR and the remainder, and the logical exclusive OR of the third logical exclusive OR and the remainder. The summation unit then furnishes the fourth logical exclusive OR as the summation result. A carry calculating unit calculates the first carry from the first, third, and fourth inputs. A selecting unit selects either the carry input or the second input according to the logical exclusive OR of the logical exclusive OR of any two of the first through fourth inputs and the logical exclusive OR of the remainder, and then furnishes the selected one as the second carry.