Set the First active predicate element to true
This instruction sets the First active element in the destination predicate to true, otherwise elements from the source predicate are passed through unchanged. This instruction sets the First (N), None (Z), and !Last (C) condition flags based on the predicate result, and sets the V flag to zero.
| 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 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | Pg | 0 | Pdn | ||||||
| op | S | ||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8; let g : integer = UInt(Pg); let dn : integer = UInt(Pdn);
| <Pdn> |
Is the name of the source and destination scalable predicate register, encoded in the "Pdn" field. |
| <Pg> |
Is the name of the governing scalable predicate register, encoded in the "Pg" field. |
CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let mask : bits(PL) = P{}(g); var result : bits(PL) = P{}(dn); var first : integer = -1; let psize : integer{} = esize DIV 8; for e = 0 to elements-1 do if ActivePredicateElement{PL}(mask, e, esize) && first == -1 then first = e; end; end; if first >= 0 then result[first*:psize] = ZeroExtend{psize}('1'); end; PSTATE.[N,Z,C,V] = PredTest{PL}(mask, result, esize); P{PL}(dn) = result;
If FEAT_SME is implemented and the PE is in Streaming SVE mode, then any subsequent instruction which is dependent on the NZCV condition flags written by this instruction might be significantly delayed.
2026-03_rel 2026-03-26 20:48:11
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