Cortex-M3 Devices Generic User Guide: 3.6.2. UMULL, UMLAL, SMULL, and SMLAL

3.6.2. UMULL, UMLAL, SMULL, and SMLAL

Signed and Unsigned Long Multiply, with optional Accumulate, using 32-bit operands and producing a 64-bit result.

Syntax

op{cond} RdLo, RdHi, Rn, Rm

where:

op

Is one of:

UMULL: Unsigned Long Multiply.
UMLAL: Unsigned Long Multiply, with Accumulate.
SMULL: Signed Long Multiply.
SMLAL: Signed Long Multiply, with Accumulate.

cond

Is an optional condition code, see Conditional execution.

RdHi, RdLo

Are the destination registers. For UMLAL and SMLAL they also hold the accumulating value.

Rn, Rm

Are registers holding the operands.

Operation

The UMULL instruction interprets the values from Rn and Rm as unsigned integers. It multiplies these integers and places the least significant 32 bits of the result in RdLo, and the most significant 32 bits of the result in RdHi.

The UMLAL instruction interprets the values from Rn and Rm as unsigned integers. It multiplies these integers, adds the 64-bit result to the 64-bit unsigned integer contained in RdHi and RdLo, and writes the result back to RdHi and RdLo.

The SMULL instruction interprets the values from Rn and Rm as two’s complement signed integers. It multiplies these integers and places the least significant 32 bits of the result in RdLo, and the most significant 32 bits of the result in RdHi.

The SMLAL instruction interprets the values from Rn and Rm as two’s complement signed integers. It multiplies these integers, adds the 64-bit result to the 64-bit signed integer contained in RdHi and RdLo, and writes the result back to RdHi and RdLo.

Restrictions

In these instructions:

do not use SP and do not use PC
RdHi and RdLo must be different registers.

Condition flags

These instructions do not affect the condition code flags.

Examples

    UMULL       R0, R4, R5, R6   ; Unsigned (R4,R0) = R5 x R6
    SMLAL       R4, R5, R3, R8   ; Signed (R5,R4) = (R5,R4) + R3 x R8

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