Cortex-M3 Devices Generic User Guide: 3.6.1. MUL, MLA, and MLS

3.6.1. MUL, MLA, and MLS

Multiply, Multiply with Accumulate, and Multiply with Subtract, using 32-bit operands, and producing a 32-bit result.

Syntax

MUL{S}{cond} {Rd,} Rn, Rm ; Multiply

MLA{cond} Rd, Rn, Rm, Ra  ; Multiply with accumulate

MLS{cond} Rd, Rn, Rm, Ra  ; Multiply with subtract

where:

cond: Is an optional condition code, see Conditional execution.
S: Is an optional suffix. If S is specified, the condition code flags are updated on the result of the operation, see Conditional execution.
Rd: Specifies the destination register. If Rd is omitted, the destination register is Rn.
Rn, Rm: Are registers holding the values to be multiplied.
Ra: Is a register holding the value to be added or subtracted from.

Operation

The MUL instruction multiplies the values from Rn and Rm, and places the least significant 32 bits of the result in Rd.

The MLA instruction multiplies the values from Rn and Rm, adds the value from Ra, and places the least significant 32 bits of the result in Rd.

The MLS instruction multiplies the values from Rn and Rm, subtracts the product from the value from Ra, and places the least significant 32 bits of the result in Rd.

The results of these instructions do not depend on whether the operands are signed or unsigned.

Restrictions

In these instructions, do not use SP and do not use PC.

If you use the S suffix with the MUL instruction:

Rd, Rn, and Rm must all be in the range R0 to R7
Rd must be the same as Rm
you must not use the cond suffix.

Condition flags

If S is specified, the MUL instruction:

updates the N and Z flags according to the result
does not affect the C and V flags.

Examples

    MUL     R10, R2, R5     ; Multiply, R10 = R2 x R5
    MLA     R10, R2, R1, R5 ; Multiply with accumulate, R10 = (R2 x R1) + R5
    MULS    R0, R2, R2      ; Multiply with flag update, R0 = R2 x R2
    MULLT   R2, R3, R2      ; Conditionally multiply, R2 = R3 x R2
    MLS     R4, R5, R6, R7  ; Multiply with subtract, R4 = R7 - (R5 x R6).

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