vsetvli

{
  let VLEN_pow      = get_vlen_pow();
  let ELEN_pow      = get_elen_pow();
  let LMUL_pow_ori  = get_lmul_pow();
  let SEW_pow_ori   = get_sew_pow();
  let ratio_pow_ori = SEW_pow_ori - LMUL_pow_ori;

  /* set vtype */
  match op {
    VSETVLI => {
      vtype->bits() = 0b0 @ zeros(sizeof(xlen) - 9) @ ma @ ta @ sew @ lmul
    },
    VSETVL  => {
      let rs2 : regidx = sew[1 .. 0] @ lmul;
      vtype->bits() = X(rs2)
    }
  };

  /* check legal SEW and LMUL and calculate VLMAX */
  let LMUL_pow_new = get_lmul_pow();
  let SEW_pow_new  = get_sew_pow();
  if SEW_pow_new > LMUL_pow_new + ELEN_pow then {
    /* Note: Implementations can set vill or trap if the vtype setting is not supported.
     * TODO: configuration support for both solutions
     */
    vtype->bits() = 0b1 @ zeros(sizeof(xlen) - 1); /* set vtype.vill */
    vl = zeros();
    print_reg("CSR vtype <- " ^ BitStr(vtype.bits()));
    print_reg("CSR vl <- " ^ BitStr(vl));
    return RETIRE_SUCCESS
  };
  let VLMAX = int_power(2, VLEN_pow + LMUL_pow_new - SEW_pow_new);

  /* set vl according to VLMAX and AVL */
  if (rs1 != 0b00000) then { /* normal stripmining */
    let rs1_val = X(rs1);
    let AVL = unsigned(rs1_val);
    vl = if AVL <= VLMAX then to_bits(sizeof(xlen), AVL)
         else if AVL < 2 * VLMAX then to_bits(sizeof(xlen), (AVL + 1) / 2)
         else to_bits(sizeof(xlen), VLMAX);
    /* Note: ceil(AVL / 2) <= vl <= VLMAX when VLMAX < AVL < (2 * VLMAX)
     * TODO: configuration support for either using ceil(AVL / 2) or VLMAX
     */
    X(rd) = vl;
  } else if (rd != 0b00000) then { /* set vl to VLMAX */
    let AVL = unsigned(ones(sizeof(xlen)));
    vl = to_bits(sizeof(xlen), VLMAX);
    X(rd) = vl;
  } else { /* keep existing vl */
    let AVL = unsigned(vl);
    let ratio_pow_new = SEW_pow_new - LMUL_pow_new;
    if (ratio_pow_new != ratio_pow_ori) then {
      /* Note: Implementations can set vill or trap if the vtype setting is not supported.
       * TODO: configuration support for both solutions
       */
      vtype->bits() = 0b1 @ zeros(sizeof(xlen) - 1); /* set vtype.vill */
      vl = zeros();
    }
  };
  print_reg("CSR vtype <- " ^ BitStr(vtype.bits()));
  print_reg("CSR vl <- " ^ BitStr(vl));

  /* reset vstart to 0 */
  vstart = zeros();
  print_reg("CSR vstart <- " ^ BitStr(vstart));

  RETIRE_SUCCESS
}