TST (immediate) Test bits (immediate) This instruction performs a bitwise AND of a register value and an immediate value, and discards the results. It updates the condition flags based on the result. 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. ANDS (immediate) 1 1 1 0 0 1 0 0 1 1 1 1 1 0 0 TST <Wn>, #<imm> ANDS WZR, <Wn>, #<imm> Unconditionally 1 TST <Xn>, #<imm> ANDS XZR, <Xn>, #<imm> Unconditionally <Wn> Is the 32-bit name of the general-purpose source register, encoded in the "Rn" field. <imm> For the 32-bit variant: is the bitmask immediate, encoded in "imms:immr". <imm> For the 64-bit variant: is the bitmask immediate, encoded in "N:imms:immr". <Xn> Is the 64-bit name of the general-purpose source register, encoded in the "Rn" field.