Subtract immediate (unpredicated)
This instruction subtracts an unsigned immediate from each element of the source vector, and destructively places the results in the corresponding elements of the source vector. This instruction is unpredicated.
The immediate is an unsigned value in the range 0 to 255, and for element widths of 16 bits or higher it may also be a positive multiple of 256 in the range 256 to 65280.
The immediate is encoded in 8 bits with an optional left shift by 8. The preferred disassembly when the shift option is specified is "#<imm>, LSL #8". However an assembler and disassembler may also allow use of the shifted 16-bit value unless the immediate is 0 and the shift amount is 8, which must be unambiguously described as "#0, LSL #8".
| 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 |
| 0 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | size | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | sh | imm8 | Zdn | ||||||||||||
| opc | |||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; if size::sh == '001' then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let dn : integer = UInt(Zdn); var imm : integer = UInt(imm8); if sh == '1' then imm = imm << 8; end;
| <Zdn> |
Is the name of the source and destination scalable vector register, encoded in the "Zdn" field. |
| <T> |
Is the size specifier,
encoded in
|
| <imm> |
Is an unsigned immediate in the range 0 to 255, encoded in the "imm8" field. |
| <shift> |
Is the optional left shift to apply to the immediate, defaulting to LSL #0 and
encoded in
|
CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let elements : integer = VL DIV esize; let operand1 : bits(VL) = Z{}(dn); var result : bits(VL); for e = 0 to elements-1 do let element1 : bits(esize) = operand1[e*:esize]; result[e*:esize] = element1 - imm; end; Z{VL}(dn) = result;
This instruction is a data-independent-time instruction as described in About PSTATE.DIT.
This instruction might be immediately preceded in program order by a MOVPRFX instruction. The MOVPRFX must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is CONSTRAINED UNPREDICTABLE:
2026-03_rel 2026-03-26 20:48:11
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