Circuitry for performing operations on binary numbers

Circuitry for adding a first binary number having a plurality of bits to a second binary number having a plurality of bits to produce a third binary number having a plurality of bits or a fourth binary number having a plurality of bits and corresponding to the third binary number plus one, said circuitry comprising a plurality of stages wherein each stage includes:

• a first input for receiving a bit of the first binary number;
• a second input for receiving a bit of the second binary number having the same binary weight as the bit received at the first input;
• and
• output means for producing a bit of the third binary number or a bit of the fourth binary number, wherein said output means comprises exclusive OR means for combining a first signal and a second signal to produce a bit of the third binary number or the first signal and a third signal to produce a bit of the fourth binary number, said exclusive OR means operating in dependence on the value of a single independent control signal being supplied directly to an output stage.

Circuitry for performing subtraction operations on a first binary number having a plurality of bits and a second binary number having a plurality of bits to produce a third binary number having a plurality of bits or a fourth binary number having a plurality of bits, said circuitry comprising a plurality of stages wherein each stage includes:

• a first input for receiving a bit of the first binary number;
• a second input for receiving a bit of the second binary number having the same binary weight as the bit received at the first input and having been inverted;
• and
• output means for producing a bit of the third binary number or a bit of the fourth binary number, wherein said output means comprises exclusive OR means for combining a first signal and a second signal to produce a bit of the third binary number or the first signal and a third signal to produce a bit of the fourth binary number, said exclusive OR means being supplied by logic circuitry comprising an OR gate and an inverter which are supplied in parallel with said second signal, said logic circuitry being operable to produce said second or third signal in dependence upon a control signal.

Circuitry for providing the positive difference between a first binary number having a plurality of bits and a second binary number having a plurality of bits to produce a third binary number having a plurality of bits or a fourth binary number having a plurality of bits, said circuitry comprising a plurality of stages wherein each stage includes:

• a first input for receiving a bit of the first binary number;
• a second input for receiving a bit of the second binary number having the same binary weight as the bit received at the first input and having been inverted;
• and
• output means for producing a bit of the third binary number or a bit of the fourth binary number, wherein said output means comprises exclusive OR means for combining a first signal and a second signal to produce a bit of the third binary number or a first signal and a third signal to produce a bit of the fourth binary number, said exclusive OR means being supplied by logic circuitry comprising an OR gate and an inverter which are supplied in parallel with said second signal, said logic circuitry being operable to produce said second or third signal in dependence upon the value of a control signal supplied from carry and propagation circuitry disposed between at least one of said inputs and said output means.