mul

Multiply (A32)

MUL{S}<c> <Rd>, <Rn>, <Rm>

Multiplies two 32-bit values.

Details

Multiply computes the product of Rn and Rm and stores the low 32 bits in Rd; the high 32 bits are discarded. If the S bit is set, the N and Z flags are updated based on the result; the C and V flags are unpredictable. This is an A32 instruction available in all privilege levels.

Pseudocode Operation

product ← Rn * Rm
Rd ← product[31:0]
if S == 1 then
  N ← Rd[31]
  Z ← (Rd == 0)
  C ← unpredictable
  V ← unpredictable

Example

MUL r0, r1, r2

Encoding

Binary Layout
cond
0000
000
0
Rd
0000
Rm
1001
Rn
 
Format Multiply
Opcode 0x00000090
Extension A32 (Base)

Operands

  • Rd
    Destination general-purpose register
  • Rn
    First source / base general-purpose register
  • Rm
    Second source / offset general-purpose register

Reference (Arm AArch32 ISA)

Instruction Forms

Encoding Instruction ISA Bit pattern
0x00000090 MUL{<c>}{<q>} <Rd>, <Rn>{, <Rm>} A32 cond | 0000 | 000 | 0 | Rd | 0000 | Rm | 1001 | Rn
0x4340 MUL<c>{<q>} <Rdm>, <Rn>{, <Rdm>} T32 010000 | 1101 | Rn | Rdm
0xFB00F000 MUL<c>.W <Rd>, <Rn>{, <Rm>} T32 111110110 | 000 | Rn | 1111 | Rd | 00 | 00 | Rm

Description

Multiply multiplies two register values. The least significant 32 bits of the result are written to the destination register. These 32 bits do not depend on whether the source register values are considered to be signed values or unsigned values. Optionally, it can update the condition flags based on the result. In the T32 instruction set, this option is limited to only a few forms of the instruction. Use of this option adversely affects performance on many implementations.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    operand1 = SInt(R[n]);  // operand1 = UInt(R[n]) produces the same final results
    operand2 = SInt(R[m]);  // operand2 = UInt(R[m]) produces the same final results
    result = operand1 * operand2;
    R[d] = result<31:0>;
    if setflags then
        PSTATE.N = result<31>;
        PSTATE.Z = IsZeroBit(result<31:0>);
        // PSTATE.C, PSTATE.V unchanged