Chapter 6 Applied Instructions 4. Multiplying 32-bit binary values: D +1 D D D 2 S 2 S S 1 S 1 +1 +1 +2 +3 b31...b16 b15...b0 b63...b48 b47...b32 b31...b16 b15...b0 b31...b16 b15...b0 b31 is the sign bit. b31 is the sign bit. b63, i.e. b15 in D+3, is the sign bit. * = The product is a 64-bit value, and is stored in the register (D+3, D+2, D+1, D0), which is composed of 64 bits. When the sign bit b63 is 0, the product is a positive value. When the sign bit b63 is 1, the product is a negative value. Example The instruction multiplies the 16-bit value in D0 by the 16-bit value in D10, and stores the 32-bit product in (D21, D20).
The data in D21 is the higher 16-bit data, whereas the data in D20 is the lower 16-bit data. Whether the result is a positive value or a negative value depends on the state of the highest bit b31. When b31 is OFF, the result is a positive value. When b31 is ON, the result is a negative value. 6_ D0 Ч D10 = (D21, D20) 16-bit value Ч 16-bit value = 32-bit value 6-53