Base Instructions | SIMD&FP Instructions | SVE Instructions | SME Instructions | Index by Encoding | Shared Pseudocode | Proprietary Notice

## PFIRST

Set the first active predicate element to true

Sets the first active element in the destination predicate to true, otherwise elements from the source predicate are passed through unchanged. Sets the First (N), None (Z), !Last (C) condition flags based on the predicate result, and 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
|  | S |  |  |  |  |

####

PFIRST <Pdn>.B, <Pg>, <Pdn>.B

if !HaveSVE() && !HaveSME() then UNDEFINED; constant integer esize = 8; integer g = UInt(Pg); integer dn = UInt(Pdn);

### Assembler Symbols

<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.

### Operation

CheckSVEEnabled(); constant integer VL = CurrentVL; constant integer PL = VL DIV 8; constant integer elements = VL DIV esize; bits(PL) mask = P[g, PL]; bits(PL) result = P[dn, PL]; integer first = -1; for e = 0 to elements-1 if ElemP[mask, e, esize] == '1' && first == -1 then first = e; if first >= 0 then ElemP[result, first, esize] = '1'; PSTATE.<N,Z,C,V> = PredTest(mask, result, esize); P[dn, PL] = result;

### Operational information

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.

Base Instructions | SIMD&FP Instructions | SVE Instructions | SME Instructions | Index by Encoding | Shared Pseudocode | Proprietary Notice

Internal version only: isa v33.53, AdvSIMD v29.11, pseudocode v2022-09_rel, sve v2022-09_rel ; Build timestamp: 2022-09-30T16:37

Copyright © 2010-2022 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.