Freescale Semiconductor SC140 specifications Multiplication, Division, Unsigned Arithmetic

DALU

2.2.2.3 Multiplication

Most of the operations are performed identically in fractional and integer arithmetic. However, the multiplication operation is not the same for integer and fractional arithmetic. As illustrated in Figure 2-4, fractional and integer multiplication differ by a 1-bit shift. Any binary multiplication of two N-bit signed numbers gives a signed result that is 2N-1 bits in length. This 2N-1 bit result must then be correctly placed into a field of 2N-bits to correctly fit into the on-chip registers. For correct fractional multiplication, an extra 0-bit is placed at the LSB to give a 2N-bit result. For correct integer multiplication, an extra sign bit is placed at the MSB to give a 2N-bit result.

Signed Multiplication: N x N --> 2N – 1 Bits

				Integer
S						S
					X
						Signed Multiplier
	S	S	HP				LP
				2N – 1 product
			sign extension
				2N bits

			Fractional
S						S
					X
							Signed Multiplier
	S	HP					LP	0
			2N – 1 product
							zero fill
				2N bits

Figure 2-4. Fractional and Integer Multiplication

The MPY, MAC, MPYR, and MACR instructions perform fractional multiplication and fractional multiply-accumulation. The IMPY and the IMAC instructions perform integer multiplication.

2.2.2.4 Division

Fractional division of both positive and signed values is supported using the DIV instruction. The dividend (numerator) is a 32-bit fraction and the divisor (denominator) is a 16-bit fraction. For a detailed description of the DIV instruction, see Appendix A, “SC140 DSP Core Instruction Set.”

2.2.2.5 Unsigned Arithmetic

Unsigned arithmetic can be performed on the SC140 core architecture. Most of the unsigned arithmetic instructions are performed the same as the signed instructions. However, some operations require special hardware and are implemented as separate instructions.

2.2.2.5.1 Unsigned Multiplication

Unsigned multiplication (MPYUU, MACUU) and mixed unsigned-signed multiplication (MPYSU, MACSU) are used to support double precision, as described in Section 2.2.2.8, “Multi-Precision Arithmetic Support.” These instructions can be used for unsigned arithmetic multiplication.

2-20 SC140 DSP Core Reference Manual