USADA8 -- AArch32

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USADA8 -- AArch32

USADA8

Unsigned Sum of Absolute Differences and Accumulate performs four unsigned 8-bit subtractions, and adds the absolute values of the differences to a 32-bit accumulate operand.

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	1	1	0	0	0	Rd				!= 1111				Rm				0	0	0	1	Rn
cond																Ra

Encoding

USADA8{<c>}{<q>} <Rd>, <Rn>, <Rm>, <Ra>

Decode for this encoding

if Ra == '1111' then See("USAD8"); end; let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let a : integer = UInt(Ra); 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	1	0	1	1	1	Rn				!= 1111				Rd				0	0	0	0	Rm
									op1							Ra										op2

Encoding

USADA8{<c>}{<q>} <Rd>, <Rn>, <Rm>, <Ra>

Decode for this encoding

if Ra == '1111' then See("USAD8"); end; let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let a : integer = UInt(Ra); // 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.

<Ra>	Is the third general-purpose source register holding the addend, encoded in the "Ra" field.

Operation

if ConditionPassed() then EncodingSpecificOperations(); let absdiff1 : integer = Abs(UInt(R(n)[7:0]) - UInt(R(m)[7:0])); let absdiff2 : integer = Abs(UInt(R(n)[15:8]) - UInt(R(m)[15:8])); let absdiff3 : integer = Abs(UInt(R(n)[23:16]) - UInt(R(m)[23:16])); let absdiff4 : integer = Abs(UInt(R(n)[31:24]) - UInt(R(m)[31:24])); let result : integer = UInt(R(a)) + absdiff1 + absdiff2 + absdiff3 + absdiff4; R(d) = result[31:0]; end;

Operational information

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

2025-09_rel_asl1 2026-03-12 12:57:38