Samsung S3C2440A MULTIPLY AND MULTIPLY-ACCUMULATE (MUL, MLA)

ARM INSTRUCTION SET S3C2440A RISC MICROPROCESSOR
3-22
MULTIPLY AND MULTIPLY-ACCUMULATE (MUL, MLA)
The instruction is only executed if the condition is true. The various conditions are defined in Table 3-2. The
instruction encoding is shown in Figure 3-12.
The multiply and multiply-accumulate instructions use an 8 bit Booth's algorithm to perform integer multiplication.
31 27 19 15
Cond
28 16 111221 20
SRd Rn
[15:12][11:8][3:0] Operand Registers
[19:16] Destination Register
[20] Set Condition Code
0 = Do not after condition codes
1 = Set condition codes
[21] Accumulate
0 = Multiply only
1 = Multiply and accumulate
[31:28] Condition Field
22
1001
Rs RmA000000
87 43 0
Figure 3-12. Multiply Instructions
The multiply form of the instruction gives Rd:=Rm*Rs. Rn is ignored, and should be set to zero for com patibility
with possible future upgrades to the instruction set. The multiply-accumulate form gives Rd:=Rm *Rs+Rn, which
can save an explicit ADD instruction in some circumstances. Both form s of the instruction work on operands which
may be considered as signed (2's complement) or unsigned integers.
The results of a signed multiply and of an unsigned multiply of 32 bit operands differ only in the upper 32 bits - the
low 32 bits of the signed and unsigned results are identical. As these instructions only produce the low 32 bits of a
multiply, they can be used for both signed and unsigned multiplies.
For example consider the multiplication of the operands:
Operand A Operand B Result
0xFFFFFFF6 0x0000001 0xFFFFFF38