Decrement vector by count of true predicate elements
This instruction determines the number of true elements in the source predicate and then uses the result to decrement all destination vector elements.
The predicate size specifier may be omitted in assembler source code, but this is deprecated and will be prohibited in a future release of the architecture.
| 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 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | Pm | Zdn | ||||||||
| op | D | opc2 | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; if size == '00' then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let m : integer = UInt(Pm); let dn : integer = UInt(Zdn);
| <Zdn> |
Is the name of the source and destination scalable vector register, encoded in the "Zdn" field. |
| <T> |
Is the size specifier,
encoded in
|
| <Pm> |
Is the name of the source scalable predicate register, encoded in the "Pm" field. |
CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let operand1 : bits(VL) = Z{}(dn); let operand2 : bits(PL) = P{}(m); var result : bits(VL); var count : integer = 0; for e = 0 to elements-1 do if ActivePredicateElement{PL}(operand2, e, esize) then count = count + 1; end; end; for e = 0 to elements-1 do result[e*:esize] = operand1[e*:esize] - count; end; Z{VL}(dn) = result;
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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