SADD8 -- AArch32

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SADD8 -- AArch32

SADD8

Signed Add 8 performs four 8-bit signed integer additions, and writes the results to the destination register. It sets PSTATE.GE according to the results of the additions.

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	0	0	0	1	Rn				Rd				(1)	(1)	(1)	(1)	1	0	0	1	Rm
cond									op1															B	op2

Encoding

SADD8{<c>}{<q>} {<Rd>, }<Rn>, <Rm>

Decode for this encoding

let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); if d == 15 || n == 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	1	0	0	0	Rn				1	1	1	1	Rd				0	0	0	0	Rm
									op1																U	H	S

Encoding

SADD8{<c>}{<q>} {<Rd>, }<Rn>, <Rm>

Decode for this encoding

let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); // Armv8-A removes UNPREDICTABLE for R13 if d == 15 || n == 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.

Operation

if ConditionPassed() then EncodingSpecificOperations(); let sum1 : integer = SInt(R(n)[7:0]) + SInt(R(m)[7:0]); let sum2 : integer = SInt(R(n)[15:8]) + SInt(R(m)[15:8]); let sum3 : integer = SInt(R(n)[23:16]) + SInt(R(m)[23:16]); let sum4 : integer = SInt(R(n)[31:24]) + SInt(R(m)[31:24]); R(d)[7:0] = sum1[7:0]; R(d)[15:8] = sum2[7:0]; R(d)[23:16] = sum3[7:0]; R(d)[31:24] = sum4[7:0]; PSTATE.GE[0] = if sum1 >= 0 then '1' else '0'; PSTATE.GE[1] = if sum2 >= 0 then '1' else '0'; PSTATE.GE[2] = if sum3 >= 0 then '1' else '0'; PSTATE.GE[3] = if sum4 >= 0 then '1' else '0'; 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

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	1	0	0	0	Rn				1	1	1	1	Rd				0	0	0	0	Rm
									op1																U	H	S

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	1	0	0	0	Rn				1	1	1	1	Rd				0	0	0	0	Rm
									op1																U	H	S

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	1	0	0	0	Rn				1	1	1	1	Rd				0	0	0	0	Rm
									op1																U	H	S