INDEX (immediate, scalar) -- A64

Create index starting from immediate and incremented by general-purpose register

This instruction populates the destination vector by setting the first element to the first signed immediate integer operand and monotonically incrementing the value by the second signed scalar integer operand for each subsequent element. The scalar source operand is a general-purpose register in which only the least significant bits corresponding to the vector element size are used and any remaining bits are ignored. This instruction is unpredicated.

SVE
(FEAT_SVE || FEAT_SME)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let m : integer = UInt(Rm); let d : integer = UInt(Zd); let imm : integer = SInt(imm5);

Assembler Symbols

<Zd>	Is the name of the destination scalable vector register, encoded in the "Zd" field.

<T>

Is the size specifier, encoded in size:

size	<T>
00	B
01	H
10	S
11	D

<imm>

Is the signed immediate operand, in the range -16 to 15, encoded in the "imm5" field.

<R>

Is a width specifier, encoded in size:

size	<R>
00	W
01	W
10	W
11	X

<m>	Is the number [0-30] of the source general-purpose register or the name ZR (31), encoded in the "Rm" field.

Operation

CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let elements : integer = VL DIV esize; let operand2 : bits(esize) = X{}(m); let element2 : integer = SInt(operand2); var result : bits(VL); for e = 0 to elements-1 do let index : integer = imm + e * element2; result[e*:esize] = index[esize-1:0]; end; Z{VL}(d) = result;

2026-03_rel 2026-03-26 20:48:11

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
0	0	0	0	0	1	0	0	size		1	Rm					0	1	0	0	1	0	imm5					Zd