SXTAB16 -- AArch32

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SXTAB16 -- AArch32

SXTAB16

Signed Extend and Add Byte 16 extracts two 8-bit values from a register, sign-extends them to 16 bits each, adds the results to two 16-bit values from another register, and writes the final results to the destination register. The instruction can specify a rotation by 0, 8, 16, or 24 bits before extracting the 8-bit values.

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .

A1

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
!= 1111				0	1	1	0	1	0	0	0	!= 1111				Rd				rotate		(0)	(0)	0	1	1	1	Rm
cond									U	op		Rn

Encoding

SXTAB16{<c>}{<q>} {<Rd>, }<Rn>, <Rm> {, ROR #<amount>}

Decode for this encoding

if Rn == '1111' then See("SXTB16"); end; let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let rotation : integer = UInt(rotate::'000'); if d == 15 || m == 15 then UnpredictableProcedure(); end;

T1

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
1	1	1	1	1	0	1	0	0	0	1	0	!= 1111				1	1	1	1	Rd				1	(0)	rotate		Rm
									op1		U	Rn

Encoding

SXTAB16{<c>}{<q>} {<Rd>, }<Rn>, <Rm> {, ROR #<amount>}

Decode for this encoding

if Rn == '1111' then See("SXTB16"); end; let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let rotation : integer = UInt(rotate::'000'); // Armv8-A removes UNPREDICTABLE for R13 if d == 15 || m == 15 then UnpredictableProcedure(); end;

For more information about the CONSTRAINED UNPREDICTABLE behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<c>	See Standard assembler syntax fields.

<q>	See Standard assembler syntax fields.

<Rd>	Is the general-purpose destination register, encoded in the "Rd" field.

<Rn>	Is the first general-purpose source register, encoded in the "Rn" field.

<Rm>	Is the second general-purpose source register, encoded in the "Rm" field.

Is the rotate amount, encoded in rotate:

rotate	<amount>
00	[absent]
01	8
10	16
11	24

Operation

if ConditionPassed() then EncodingSpecificOperations(); let rotated : bits(32) = ROR(R(m), rotation); R(d)[15:0] = R(n)[15:0] + SignExtend{16}(rotated[7:0]); R(d)[31:16] = R(n)[31:16] + SignExtend{16}(rotated[23:16]); end;

Operational information

This instruction is a data-independent-time instruction as described in About the DIT bit.

2026-03_rel 2026-03-26 20:48:11