Instruction Syntax

Mnemonic	Format	Flags
mullw	rD,rA,rB	OE = 0, Rc = 0
mullw.	rD,rA,rB	OE = 0, Rc = 1
mullwo	rD,rA,rB	OE = 1, Rc = 0
mullwo.	rD,rA,rB	OE = 1, Rc = 1

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	011111 (0x1F)
rD	6-10	Destination register
rA	11-15	Source register A
rB	16-20	Source register B
OE	21	Overflow Exception
XO	22-29	150 (Extended opcode)
Rc	30-31	Record Condition Register

Operation

rD ← (rA × rB)[32:63]

The contents of registers rA and rB are multiplied as signed 32-bit integers, and the low-order 32 bits of the result are placed into rD.

Note: The mullw instruction performs signed multiplication and returns the low-order word of the result. This is the most commonly used multiplication instruction for 32-bit arithmetic.

Affected Registers

Condition Register (CR0 field)

(if Rc = 1)

• LT (Less Than)
• GT (Greater Than)
• EQ (Equal)
• SO (Summary Overflow)

Note: CR0 field reflects the sign of the result.

XER (Exception Register)

(if OE = 1)

• SO (Summary Overflow)
• OV (Overflow)

For more information on condition codes see Section 2.1.3, "Condition Register," and Section 2.1.5, "XER Register," in the PowerPC Microprocessor Family: The Programming Environments manual.

Examples

Basic Multiplication

mullw r3, r1, r2     # r3 = r1 * r2
mullw. r3, r1, r2    # Same as above, but also sets condition register

Array Index Calculation

# Calculate array index: index * sizeof(element)
lwz r4, 0(r10)       # Load array index
mullw r5, r4, 4      # r5 = index * 4 (for 32-bit elements)
add r6, r7, r5       # r6 = base_address + offset

Matrix Operations

# Calculate matrix element offset: row * cols + col
mullw r8, r6, r5     # r8 = row * cols
add r9, r8, r7       # r9 = (row * cols) + col

Overflow Detection

mullwo r3, r1, r2    # Multiply with overflow exception enabled
# If overflow occurs, an exception is raised

Extended Precision Arithmetic

# Part of 64-bit multiplication using low word
mullw r6, r4, r5     # Get low word of product
mulhw r7, r4, r5     # Get high word of product
# r7:r6 contains full 64-bit result

Related Instructions

mulhw, mulhwu, mulli