3.6.9. SMUAD and SMUSD

Signed Dual Multiply Add and Signed Dual Multiply Subtract.

Syntax

op{X}{cond} Rd, Rn, Rm

Where:

op

Is one of:

SMUAD

Signed Dual Multiply Add.

SMUADX

Signed Dual Multiply Add reversed.

SMUSD

Signed Dual Multiply Subtract.

SMUSDX

Signed Dual Multiply Subtract reversed.

If X is present, the multiplications are bottom × top and top × bottom. If the X is omitted, the multiplications are bottom × bottom and top × top.

cond

Is an optional condition code. See Conditional execution.

Rd

Is the destination register.

Rn, Rm

Are registers holding the first and the second operands.

Operation

The SMUAD instruction interprets the values from the first and second operands as two signed halfwords in each operand. This instruction:

  • Optionally rotates the halfwords of the second operand.

  • Performs two signed 16 × 16-bit multiplications.

  • Adds the two multiplication results together.

  • Writes the result of the addition to the destination register.

The SMUSD instruction interprets the values from the first and second operands as two’s complement signed integers. This instruction:

  • Optionally rotates the halfwords of the second operand.

  • Performs two signed 16 × 16-bit multiplications.

  • Subtracts the result of the top halfword multiplication from the result of the bottom halfword multiplication.

  • Writes the result of the subtraction to the destination register.

Restrictions

In these instructions:

  • Do not use SP and do not use PC.

Condition flags

SMUAD, SMUADX set the Q flag if the addition overflows. The multiplications cannot overflow.

Examples

SMUAD    R0, R4, R5      ; Multiplies bottom halfword of R4 with the bottom
                         ; halfword of R5, adds multiplication of top halfword
                         ; of R4 with top halfword of R5, writes to R0.
SMUADX   R3, R7, R4      ; Multiplies bottom halfword of R7 with top halfword
                         ; of R4, adds multiplication of top halfword of R7 
                         ; with bottom halfword of R4, writes to R3.
SMUSD    R3, R6, R2      ; Multiplies bottom halfword of R4 with bottom halfword
                         ; of R6, subtracts multiplication of top halfword of R6
                         ; with top halfword of R3, writes to R3.
SMUSDX   R4, R5, R3      ; Multiplies bottom halfword of R5 with top halfword of
                         ; R3, subtracts multiplication of top halfword of R5
                         ; with bottom halfword of R3, writes to R4.
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