CALCULATING THE AVERAGE OF TWO INTEGER NUMBERS ROUNDED TOWARDS ZERO IN A SINGLE INSTRUCTION CYCLE

The average of two signed or unsigned integer numbers (A, B) rounded towards zero as prescribed in the MPEG standard is calculated in one instruction cycle by right shifting each of the operands by one bit position, summing the shifted operands, and incrementing the result as appropriate. The shifted operands are summed in an adder (302) that provides two versions of the average, one being the sum of the shifted operands and the other being the sum-plus-one of the shifted operands. A multiplexer (310) under control of a control circuit (308) selects one of the sum and sum-plus-one outputs. Incrementing (selecting the sum-plus-one output) is based on inspection of the shifted-out bits of the operands, the most significant bit of the sum, and a mode signal indicative of whether the operands are signed or unsigned values.