UQSUB8 -- AArch32

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UQSUB8

Unsigned Saturating Subtract 8 performs four unsigned 8-bit integer subtractions, saturates the results to the 8-bit unsigned integer range 0 <= x <= 2⁸ - 1, and writes the results to the destination register.

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

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;

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

Operation

if ConditionPassed() then EncodingSpecificOperations(); let diff1 : integer = UInt(R(n)[7:0]) - UInt(R(m)[7:0]); let diff2 : integer = UInt(R(n)[15:8]) - UInt(R(m)[15:8]); let diff3 : integer = UInt(R(n)[23:16]) - UInt(R(m)[23:16]); let diff4 : integer = UInt(R(n)[31:24]) - UInt(R(m)[31:24]); R(d)[7:0] = UnsignedSat{8}(diff1); R(d)[15:8] = UnsignedSat{8}(diff2); R(d)[23:16] = UnsignedSat{8}(diff3); R(d)[31:24] = UnsignedSat{8}(diff4); end;

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

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

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