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.
| 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 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | Rm | 0 | len | op | 0 | 0 | Rn | Rd | |||||||||||||
| Q | op2 | ||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_AdvSIMD) || !IsFeatureImplemented(FEAT_LUT) then EndOfDecode(Decode_UNDEF); end; if len[0] == '0' && 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{} = 4; let esize : integer{} = 8 << UInt(op); let ntblr : integer = 1 << UInt(op); let part : integer = if op == '0' then UInt(len[1]) else UInt(len);
| <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. |
| <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. |
AArch64_CheckFPAdvSIMDEnabled(); let elements : integer = 128 DIV esize; let ibase : integer = elements * part; let indices : bits(128) = V{}(m); let table1 : bits(128) = V{}(n+0); let table2 : bits(128) = if ntblr == 2 then V{128}((n+1) MOD 32) else Zeros{128}; var result : bits(128); var res : bits(esize); for e = 0 to elements-1 do let index : integer = UInt(indices[(ibase + e)*:isize]); if index < elements then res = table1[index*:esize]; else assert ntblr == 2; res = table2[(index - elements)*:esize]; end; result[e*:esize] = res; end; V{128}(d) = result;
This instruction is a data-independent-time instruction as described in About PSTATE.DIT.
2025-12_rel 2025-12-10 16:41:45
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