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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

313029282726252423222120191817161514131211109876543210
!= 111101111000Rd!= 1111Rm0001Rn
condRa

A1

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

if Ra == '1111' then SEE "USAD8";
d = UInt(Rd);  n = UInt(Rn);  m = UInt(Rm);  a = UInt(Ra);
if d == 15 || n == 15 || m == 15 then UNPREDICTABLE;

T1

15141312111098765432101514131211109876543210
111110110111Rn!= 1111Rd0000Rm
Ra

T1

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

if Ra == '1111' then SEE "USAD8";
d = UInt(Rd);  n = UInt(Rn);  m = UInt(Rm);  a = UInt(Ra);
if d == 15 || n == 15 || m == 15 then UNPREDICTABLE; // Armv8-A removes UNPREDICTABLE for R13

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();
    absdiff1 = Abs(UInt(R[n]<7:0>)   - UInt(R[m]<7:0>));
    absdiff2 = Abs(UInt(R[n]<15:8>)  - UInt(R[m]<15:8>));
    absdiff3 = Abs(UInt(R[n]<23:16>) - UInt(R[m]<23:16>));
    absdiff4 = Abs(UInt(R[n]<31:24>) - UInt(R[m]<31:24>));
    result = UInt(R[a]) + absdiff1 + absdiff2 + absdiff3 + absdiff4;
    R[d] = result<31:0>;

Operational information

If CPSR.DIT is 1, this instruction has passed its condition execution check, and does not use R15 as either its source or destination:

  • The execution time of this instruction is independent of:
    • The values of the data supplied in any of its registers.
    • The values of the NZCV flags.
  • The response of this instruction to asynchronous exceptions does not vary based on:
    • The values of the data supplied in any of its registers.
    • The values of the NZCV flags.
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