Arm® A64 Instruction Set Architecture: Future Architecture Technologies in the A architecture profile

TBX

Programmable table lookup in single vector table (merging).

Reads each element of the second source (index) vector and uses its value to select an indexed element from a table of elements in the first source vector, and places the indexed 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 the corresponding destination vector element is left unchanged.

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

if !HaveSVE2() 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 = Z[d];

for e = 0 to elements-1
    integer element2 = UInt(Elem[operand2, e, esize]);
    if element2 < elements then
        Elem[result, e, esize] = Elem[operand1, element2, esize];

Z[d] = result;

Operational information

If PSTATE.DIT is 1:

• The execution time of this instruction is independent of:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.
• The response of this instruction to asynchronous exceptions does not vary based on:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.