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LDFF1SH (scalar plus scalar)

Contiguous load first-fault signed halfwords to vector (scalar index).

Contiguous load with first-faulting behavior of signed halfwords to elements of a vector register from the memory address generated by a 64-bit scalar base and scalar index which is multiplied by 2 and added to the base address. After each element access the index value is incremented, but the index register is not updated. Inactive elements will not read Device memory or signal a fault, and are set to zero in the destination vector.

It has encodings from 2 classes: 32-bit element and 64-bit element

32-bit element

313029282726252423222120191817161514131211109876543210
10100101001Rm011PgRnZt

32-bit element

LDFF1SH { <Zt>.S }, <Pg>/Z, [<Xn|SP>{, <Xm>, LSL #1}]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer g = UInt(Pg);
integer esize = 32;
integer msize = 16;
boolean unsigned = FALSE;

64-bit element

313029282726252423222120191817161514131211109876543210
10100101000Rm011PgRnZt

64-bit element

LDFF1SH { <Zt>.D }, <Pg>/Z, [<Xn|SP>{, <Xm>, LSL #1}]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer g = UInt(Pg);
integer esize = 64;
integer msize = 16;
boolean unsigned = FALSE;

Assembler Symbols

<Zt>

Is the name of the scalable vector register to be transferred, encoded in the "Zt" 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.

Operation

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(64) base;
bits(64) addr;
bits(PL) mask = P[g];
bits(VL) result;
bits(VL) orig = Z[t];
bits(msize) data;
bits(64) offset = X[m];
constant integer mbytes = msize DIV 8;
boolean first = TRUE;
boolean fault = FALSE;
boolean faulted = FALSE;
boolean unknown = FALSE;

if HaveMTEExt() then SetNotTagCheckedInstruction(FALSE);

if n == 31 then
    CheckSPAlignment();
    base = SP[];
else
    base = X[n];

for e = 0 to elements-1
    if ElemP[mask, e, esize] == '1' then
        addr = base + UInt(offset) * mbytes;
        if first then
            // Mem[] will not return if a fault is detected for the first active element
            data = Mem[addr, mbytes, AccType_NORMAL];
            first = FALSE;
        else
            // MemNF[] will return fault=TRUE if access is not performed for any reason
            (data, fault) = MemNF[addr, mbytes, AccType_CNOTFIRST];
    else
        (data, fault) = (Zeros(msize), FALSE);

    // FFR elements set to FALSE following a supressed access/fault
    faulted = faulted || fault;
    if faulted then
        ElemFFR[e, esize] = '0';

    // Value becomes CONSTRAINED UNPREDICTABLE after an FFR element is FALSE
    unknown = unknown || ElemFFR[e, esize] == '0';
    if unknown then
        if !fault && ConstrainUnpredictableBool(Unpredictable_SVELDNFDATA) then
            Elem[result, e, esize] = Extend(data, esize, unsigned);
        elsif ConstrainUnpredictableBool(Unpredictable_SVELDNFZERO) then
            Elem[result, e, esize] = Zeros();
        else  // merge
            Elem[result, e, esize] = Elem[orig, e, esize];
    else
        Elem[result, e, esize] = Extend(data, esize, unsigned);

    offset = offset + 1;

Z[t] = result;