Arm® A64 Instruction Set Architecture: Future Architecture Technologies in the A architecture profile | LDNF1SB: Contiguous load non-fault signed bytes to vector (immediate index).

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LDNF1SB

Contiguous load non-fault signed bytes to vector (immediate index).

Contiguous load with non-faulting behavior of signed bytes to elements of a vector register from the memory address generated by a 64-bit scalar base and immediate index in the range -8 to 7 which is multiplied by the vector's in-memory size, irrespective of predication, and added to the base address. Inactive elements will not read Device memory or signal a fault, and are set to zero in the destination vector.

It has encodings from 3 classes: 16-bit element , 32-bit element and 64-bit element

16-bit element

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	0	1	0	0	1	0	1	1	1	0	1	imm4				1	0	1	Pg			Rn					Zt

16-bit element

LDNF1SB { <Zt>.H }, <Pg>/Z, [<Xn|SP>{, #<imm>, MUL VL}]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer g = UInt(Pg);
integer esize = 16;
integer msize = 8;
boolean unsigned = FALSE;
integer offset = SInt(imm4);

32-bit element

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	0	1	0	0	1	0	1	1	0	1	1	imm4				1	0	1	Pg			Rn					Zt

32-bit element

LDNF1SB { <Zt>.S }, <Pg>/Z, [<Xn|SP>{, #<imm>, MUL VL}]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer g = UInt(Pg);
integer esize = 32;
integer msize = 8;
boolean unsigned = FALSE;
integer offset = SInt(imm4);

64-bit element

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	0	1	0	0	1	0	1	1	0	0	1	imm4				1	0	1	Pg			Rn					Zt

64-bit element

LDNF1SB { <Zt>.D }, <Pg>/Z, [<Xn|SP>{, #<imm>, MUL VL}]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer g = UInt(Pg);
integer esize = 64;
integer msize = 8;
boolean unsigned = FALSE;
integer offset = SInt(imm4);

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.

<imm>

Is the optional signed immediate vector offset, in the range -8 to 7, defaulting to 0, encoded in the "imm4" 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;
constant integer mbytes = msize DIV 8;
boolean fault = FALSE;
boolean faulted = FALSE;
boolean unknown = FALSE;

if n == 31 then
    CheckSPAlignment();
    if HaveMTEExt() then SetNotTagCheckedInstruction(TRUE);
    base = SP[];
else
    if HaveMTEExt() then SetNotTagCheckedInstruction(FALSE);
    base = X[n];

addr = base + offset * elements * mbytes;
for e = 0 to elements-1
    if ElemP[mask, e, esize] == '1' then
        // 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);

    addr = addr + mbytes;

Z[t] = result;

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