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

TBL

Programmable table lookup in one or two vector table (zeroing).

Reads each element of the second source (index) vector and uses its value to select an indexed element from a table of elements consisting of one or two consecutive vector registers, where the first or only vector holds the lower numbered elements, 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.

It has encodings from 2 classes: SVE and SVE2

SVE

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

SVE2

if !HaveSVE2() then UNDEFINED;
integer esize = 8 << UInt(size);
integer n = UInt(Zn);
integer m = UInt(Zm);
integer d = UInt(Zd);
boolean double_table = TRUE;

Assembler Symbols

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(VL) indexes = Z[m];
bits(VL) result;
integer table_size = if double_table then VL*2 else VL;
integer table_elems = table_size DIV esize;
bits(table_size) table;

if double_table then
    bits(VL) top = Z[(n + 1) MOD 32];
    bits(VL) bottom = Z[n];
    table = (top:bottom)<table_size-1:0>;
else
    table = Z[n];

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

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.