ST1W (scalar plus scalar, tile slice)

Contiguous store of words from 32-bit element ZA tile slice

This instruction performs a contiguous store of words from a 32-bit element ZA tile slice. The slice number within the tile is selected by the sum of the slice index register and immediate offset, modulo the number of 32-bit elements in a vector. The immediate offset is in the range 0 to 3. The memory address is generated by a 64-bit scalar base and an optional 64-bit scalar offset which is multiplied by 4 and added to the base address. Inactive elements are not written to memory.

Encoding: SME

Variants: FEAT_SME (PROFILE_A)

313029282726252423222120191817161514131211109876543210
111000001010
mszRmVRsPgRnZAtoff2

ST1W { <ZAt><HV>.S[<Ws>, <offs>] }, <Pg>, [<Xn|SP>{, <Xm>, LSL #2}]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer g = UInt('0':Pg);
constant integer s = UInt('011':Rs);
constant integer t = UInt(ZAt);
constant integer offset = UInt(off2);
constant integer esize = 32;
constant boolean vertical = V == '1';

Operation

CheckStreamingSVEAndZAEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer dim = VL DIV esize;
bits(64) base;
bits(64) addr;
constant bits(PL) mask = P[g, PL];
bits(64) moffs = X[m, 64];
constant bits(32) index = X[s, 32];
constant integer  slice = (UInt(index) + offset) MOD dim;
bits(VL) src;
constant integer mbytes = esize DIV 8;
constant boolean contiguous = TRUE;
constant boolean nontemporal = FALSE;
constant boolean tagchecked = TRUE;
constant AccessDescriptor accdesc = CreateAccDescSME(MemOp_STORE, nontemporal, contiguous,
                                                     tagchecked);

if n == 31 then
    if (AnyActiveElement(mask, esize) ||
          ConstrainUnpredictableBool(Unpredictable_CHECKSPNONEACTIVE)) then
        CheckSPAlignment();
    base = SP[64];
else
    base = X[n, 64];

src = ZAslice[t, esize, vertical, slice, VL];
for e = 0 to dim-1
    addr = AddressAdd(base, UInt(moffs) * mbytes, accdesc);
    if ActivePredicateElement(mask, e, esize) then
        Mem[addr, mbytes, accdesc] = Elem[src, e, esize];
    moffs = moffs + 1;

Explanations

<ZAt>: Is the name of the ZA tile ZA0-ZA3 to be accessed, encoded in the "ZAt" field.
<HV>: <Ws>: Is the 32-bit name of the slice index register W12-W15, encoded in the "Rs" field.
<offs>: Is the slice index offset, in the range 0 to 3, encoded in the "off2" field.
<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 optional 64-bit name of the general-purpose offset register, defaulting to XZR, encoded in the "Rm" field.

Operational Notes

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.