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

## ST2W (scalar plus scalar)

Contiguous store two-word structures from two vectors (scalar index)

Contiguous store two-word structures, each from the same element number in two vector registers to the memory address generated by a 64-bit scalar base and a 64-bit scalar index register scaled by the element size (LSL option) and added to the base address. After each structure access the index value is incremented by two. The index register is not updated by the instruction.

Each predicate element applies to the same element number in each of the two vector registers, or equivalently to the two consecutive words in memory which make up each structure. Inactive structures are not written to memory.

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
1 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | Rm | 0 | 1 | 1 | Pg | Rn | Zt
| msz<1> | msz<0> |  |  |  |  |  |

####

ST2W { <Zt1>.S, <Zt2>.S }, <Pg>, [<Xn|SP>, <Xm>, LSL #2]

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then UNDEFINED; if Rm == '11111' then UNDEFINED; constant integer t = UInt(Zt); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant integer g = UInt(Pg); constant integer esize = 32; constant integer nreg = 2;

### Assembler Symbols

<Zt1> | Is the name of the first scalable vector register to be transferred, encoded in the "Zt" field.

<Zt2> | Is the name of the second scalable vector register to be transferred, encoded as "Zt" plus 1 modulo 32.

<Pg> | Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.

<Xn|SP> | Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

<Xm> | Is the 64-bit name of the general-purpose offset register, encoded in the "Rm" field.

### Operation

CheckSVEEnabled(); constant integer VL = CurrentVL; constant integer PL = VL DIV 8; constant integer elements = VL DIV esize; bits(64) base; constant bits(PL) mask = P[g, PL]; bits(64) offset; bits(64) addr; constant integer mbytes = esize DIV 8; array [0..1] of bits(VL) values; constant boolean contiguous = TRUE; constant boolean nontemporal = FALSE; constant boolean tagchecked = TRUE; constant AccessDescriptor accdesc = CreateAccDescSVE(MemOp_STORE, nontemporal, contiguous, tagchecked); if !AnyActiveElement(mask, esize) then if n == 31 && ConstrainUnpredictableBool(Unpredictable_CHECKSPNONEACTIVE) then CheckSPAlignment(); else if n == 31 then CheckSPAlignment(); base = if n == 31 then SP[] else X[n, 64]; offset = X[m, 64]; addr = AddressAdd(base, UInt(offset) * mbytes, accdesc); for r = 0 to nreg-1 values[r] = Z[(t+r) MOD 32, VL]; for e = 0 to elements-1 for r = 0 to nreg-1 if ActivePredicateElement(mask, e, esize) then Mem[addr, mbytes, accdesc] = Elem[values[r], e, esize]; addr = AddressIncrement(addr, mbytes, accdesc);

### Operational information

If FEAT_SVE2 is implemented or FEAT_SME is implemented, then if PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored when its governing predicate register contains the same value for each execution.

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

Internal version only: aarchmrs v2024-03_relA, pseudocode v2024-03_rel, sve v2024-03_rel ; Build timestamp: 2024-03-26T09:45

Copyright © 2010-2024 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.