Arm® A64 Instruction Set Architecture: Armv8, for Armv8-A architecture profile

TBL

Programmable table lookup in single vector table.

Reads each element of the second source (index) vector and uses its value to select an indexed element from the first source (table) vector, and places the indexed table element in the destination vector element corresponding to the index vector element. If an index value is greater than or equal to the number of vector elements then it places zero in the corresponding destination vector element.

Since the index values can select any element in a vector this operation is not naturally vector length agnostic.

if !HaveSVE() then UNDEFINED;
integer esize = 8 << UInt(size);
integer n = UInt(Zn);
integer m = UInt(Zm);
integer d = UInt(Zd);

Assembler Symbols

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(VL) operand1 = Z[n];
bits(VL) operand2 = Z[m];
bits(VL) result;

for e = 0 to elements-1
    integer idx = UInt(Elem[operand2, e, esize]);
    Elem[result, e, esize] = if idx < elements then Elem[operand1, idx, esize] else Zeros();

Z[d] = result;