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SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

Signed Multiply Accumulate (halfwords).

Syntax

op{XY}{cond} Rd, Rn, Rm

op{Y}{cond} Rd, Rn, Rm, Ra

where:

op

is one of:

SMLA Signed Multiply Accumulate Long (halfwords).

X and Y specifies which half of the source registers Rn and Rm are used as the
first and second multiply operand.

If X is B, then the bottom halfword, bits [15:0], of Rn is used. 
If X is T, then the top halfword, bits [31:16], of Rn is used.

If Y is B, then the bottom halfword, bits [15:0], of Rm is used. 
If Y is T, then the top halfword, bits [31:16], of Rm is used

SMLAW Signed Multiply Accumulate (word by halfword).

Y specifies which half of the source register Rm is used as the second multiply
operand.

If Y is T, then the top halfword, bits [31:16] of Rm is used.

If Y is B, then the bottom halfword, bits [15:0] of Rm is used.

cond

Rd

is 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 SMALBB, SMLABT, SMLATB, SMLATT instructions:



Multiplies the specified signed halfword, top or bottom, values from Rn and Rm.



Adds the value in Ra to the resulting 32-bit product.



Writes the result of the multiplication and addition in Rd.

The non-specified halfwords of the source registers are ignored.

The SMLAWB and SMLAWT instructions:



Multiply the 32-bit signed values in Rn with:



The top signed halfword of Rm, T instruction suffix.



The bottom signed halfword of Rm, B instruction suffix.



Add the 32-bit signed value in Ra to the top 32 bits of the 48-bit product 



Writes the result of the multiplication and addition in Rd.

The bottom 16 bits of the 48-bit product are ignored.

If overflow occurs during the addition of the accumulate value, the instruction sets the Q flag in the APSR. No overflow
can occur during the multiplication.

Restrictions

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

Condition Flags

If an overflow is detected, the 

Q

 flag is set.

Examples