Decrement scalar 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 the scalar destination.
| 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 | 1 | 0 | 0 | Pm | Rdn | ||||||||
| op | D | opc2 | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let m : integer = UInt(Pm); let dn : integer = UInt(Rdn);
| <Xdn> |
Is the 64-bit name of the source and destination general-purpose register, encoded in the "Rdn" field. |
| <Pm> |
Is the name of the source scalable predicate register, encoded in the "Pm" field. |
| <T> |
Is the size specifier,
encoded in
|
CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let operand1 : bits(64) = X{}(dn); let operand2 : bits(PL) = P{}(m); var count : integer = 0; for e = 0 to elements-1 do if ActivePredicateElement{PL}(operand2, e, esize) then count = count + 1; end; end; X{64}(dn) = operand1 - count;
If FEAT_SME is implemented and the PE is in Streaming SVE mode, then any subsequent instruction which is dependent on the general-purpose register written by this instruction might be significantly delayed.
2026-03_rel 2026-03-26 20:48:11
Copyright © 2010-2026 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.