LUTI2
Lookup table read with 2-bit indices
This instruction copies indexed 8-bit or 16-bit elements from the table vector
to the destination vector using packed 2-bit indices from a segment of the
source vector. A segment corresponds to a portion of the source vector
that is consumed in order to fill the destination vector. The segment is selected
by the vector segment index.
This instruction is a data-independent-time instruction as described in About PSTATE.DIT.
0
1
0
0
1
1
1
0
1
x
0
0
0
0
0
1
LUTI2 <Vd>.16B, { <Vn>.16B }, <Vm>[<index>]
1
LUTI2 <Vd>.8H, { <Vn>.8H }, <Vm>[<index>]
if !IsFeatureImplemented(FEAT_AdvSIMD) || !IsFeatureImplemented(FEAT_LUT) then
EndOfDecode(Decode_UNDEF);
end;
if op2 == '10' && op == '0' then EndOfDecode(Decode_UNDEF); end;
let d : integer{} = UInt(Rd);
let n : integer{} = UInt(Rn);
let m : integer{} = UInt(Rm);
let isize : integer{} = 2;
let esize : integer{} = if op2 == '10' then 8 else 16;
let part : integer = if op2 == '10' then UInt(len) else UInt(len::op);
<Vd>
Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
<Vn>
Is the name of the SIMD&FP table register, encoded in the "Rn" field.
<Vm>
Is the name of the SIMD&FP source register, encoded in the "Rm" field.
<index>
For the "Byte" variant: is the vector segment index, in the range 0 to 3, encoded in the "len" field.
<index>
For the "Halfword" variant: is the vector segment index, in the range 0 to 7, encoded in the "len:op" fields.
AArch64_CheckFPAdvSIMDEnabled();
let elements : integer = 128 DIV esize;
let ibase : integer = elements * part;
let indices : bits(128) = V{}(m);
let table : bits(128) = V{}(n);
var result : bits(128);
for e = 0 to elements-1 do
let index : integer = UInt(indices[(ibase + e)*:isize]);
result[e*:esize] = table[index*:esize];
end;
V{128}(d) = result;
2026-03-12 12:23:09
2025-09_rel_asl1