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LDFF1SB (scalar plus vector)

Gather load first-fault signed bytes to vector (vector index).

Gather load with first-faulting behavior of signed bytes to active elements of a vector register from memory addresses generated by a 64-bit scalar base plus vector index. The index values are optionally sign or zero-extended from 32 to 64 bits. Inactive elements will not read Device memory or signal faults, and are set to zero in the destination vector.

It has encodings from 3 classes: 32-bit unpacked unscaled offset , 32-bit unscaled offset and 64-bit unscaled offset

32-bit unpacked unscaled offset

313029282726252423222120191817161514131211109876543210
110001000xs0Zm001PgRnZt

32-bit unpacked unscaled offset

LDFF1SB { <Zt>.D }, <Pg>/Z, [<Xn|SP>, <Zm>.D, <mod>]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer m = UInt(Zm);
integer g = UInt(Pg);
integer esize = 64;
integer msize = 8;
integer offs_size = 32;
boolean unsigned = FALSE;
boolean offs_unsigned = xs == '0';
integer scale = 0;

32-bit unscaled offset

313029282726252423222120191817161514131211109876543210
100001000xs0Zm001PgRnZt

32-bit unscaled offset

LDFF1SB { <Zt>.S }, <Pg>/Z, [<Xn|SP>, <Zm>.S, <mod>]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer m = UInt(Zm);
integer g = UInt(Pg);
integer esize = 32;
integer msize = 8;
integer offs_size = 32;
boolean unsigned = FALSE;
boolean offs_unsigned = xs == '0';
integer scale = 0;

64-bit unscaled offset

313029282726252423222120191817161514131211109876543210
11000100010Zm101PgRnZt

64-bit unscaled offset

LDFF1SB { <Zt>.D }, <Pg>/Z, [<Xn|SP>, <Zm>.D]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer m = UInt(Zm);
integer g = UInt(Pg);
integer esize = 64;
integer msize = 8;
integer offs_size = 64;
boolean unsigned = FALSE;
boolean offs_unsigned = TRUE;
integer scale = 0;

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.

<Zm>

Is the name of the offset scalable vector register, encoded in the "Zm" field.

<mod> Is the index extend and shift specifier, encoded in xs:
xs <mod>
0 UXTW
1 SXTW

Operation

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(64) base;
bits(64) addr;
bits(VL) offset;
bits(PL) mask = P[g];
bits(VL) result;
bits(VL) orig = Z[t];
bits(msize) data;
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];
offset = Z[m];

for e = 0 to elements-1
    if ElemP[mask, e, esize] == '1' then
        integer off = Int(Elem[offset, e, esize]<offs_size-1:0>, offs_unsigned);
        addr = base + (off << scale);
        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_NONFAULT];
    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);

Z[t] = result;
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