LUTI4

Lookup table read with 4-bit indices. This instruction copies indexed 8-bit or 16-bit elements from the one or two table vectors to the destination vector using packed 4-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.

Advanced SIMD
(FEAT_LUT)

313029282726252423222120191817161514131211109876543210
01001110010Rm0lenop00RnRd
Qop2

Byte (len == x1 && op == 0)

LUTI4 <Vd>.16B, { <Vn>.16B }, <Vm>[<index>]

Halfword (op == 1)

LUTI4 <Vd>.8H, { <Vn1>.8H, <Vn2>.8H }, <Vm>[<index>]

if !IsFeatureImplemented(FEAT_LUT) then UNDEFINED; if len<0> == '0' && op == '0' then UNDEFINED; constant integer isize = 4; constant integer esize = 8 << UInt(op); integer ntblr = 1 << UInt(op); integer n = UInt(Rn); integer m = UInt(Rm); integer d = UInt(Rd); integer part = if op == '0' then UInt(len<1>) else UInt(len);

Assembler Symbols

<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 1, encoded in the "len<1>" field.

For the halfword variant: is the vector segment index, in the range 0 to 3, encoded in the "len" field.

<Vn1>

Is the name of the first SIMD&FP table register, encoded in the "Rn" field.

<Vn2>

Is the name of the second SIMD&FP table register, encoded as "Rn" plus 1 modulo 32.

Operation

CheckFPAdvSIMDEnabled64(); integer elements = 128 DIV esize; integer ibase = elements * part; bits(128) indices = V[m, 128]; bits(128) table1 = V[n+0, 128]; bits(128) table2 = if ntblr == 2 then V[(n+1) MOD 32, 128] else Zeros(128); bits(128) result; bits(esize) res; for e = 0 to elements-1 integer index = UInt(Elem[indices, ibase+e, isize]); if index < elements then res = Elem[table1, index, esize]; else assert ntblr == 2; res = Elem[table2, index-elements, esize]; Elem[result, e, esize] = res; V[d, 128] = result;

Operational information

If PSTATE.DIT is 1:


Internal version only: aarchmrs v2024-03_relA, pseudocode v2024-03_rel, sve v2024-03_rel ; Build timestamp: 2024-03-26T09:45

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