if (c.isLowSurrogate() || !low.isLowSurrogate()) {
              '?'.code
            } else {
              i++
              0x010000 + (c.code and 0x03ff shl 10 or (low.code and 0x03ff))
            }
          }

          else -> c.code
        }
      i++
    }
    return result
  }

  private val Int.punycodeDigit: Int
    get() =

	{_Star, "*", Mul, precMul},
	{_Operator, "/", Div, precMul},
	{_Operator, "%", Rem, precMul},
	{_Operator, "&", And, precMul},
	{_Operator, "&^", AndNot, precMul},
	{_Operator, "<<", Shl, precMul},
	{_Operator, ">>", Shr, precMul},

	// assignment operations
	{_AssignOp, "+=", Add, precAdd},
	{_AssignOp, "-=", Sub, precAdd},
	{_AssignOp, "|=", Or, precAdd},
	{_AssignOp, "^=", Xor, precAdd},

		return i*_W + uint(bits.TrailingZeros(uint(x[i]))), true
	}
	return 0, false
}

func same(x, y nat) bool {
	return len(x) == len(y) && len(x) > 0 && &x[0] == &y[0]
}

// z = x << s
func (z nat) shl(x nat, s uint) nat {
	if s == 0 {
		if same(z, x) {
			return z
		}
		if !alias(z, x) {
			return z.set(x)
		}
	}

	m := len(x)
	if m == 0 {
		return z[:0]
	}
	// m > 0

// with op == [token.SHL] or [token.SHR] (<< or >>). x must be
// an [Int] or an [Unknown]. If x is [Unknown], the result is x.
func Shift(x Value, op token.Token, s uint) Value {
	switch x := x.(type) {
	case unknownVal:
		return x

	case int64Val:
		if s == 0 {
			return x
		}
		switch op {
		case token.SHL:
			z := i64toi(x).val
			return makeInt(z.Lsh(z, s))

	/*11081*/ uint16(xSetOp), uint16(SHL),
	/*11083*/ uint16(xArgRM16),
	/*11084*/ uint16(xArg1),
	/*11085*/ uint16(xMatch),
	/*11086*/ uint16(xSetOp), uint16(SHL),
	/*11088*/ uint16(xArgRM32),
	/*11089*/ uint16(xArg1),
	/*11090*/ uint16(xMatch),
	/*11091*/ uint16(xCondDataSize), 11081, 11086, 11095,
	/*11095*/ uint16(xSetOp), uint16(SHL),
	/*11097*/ uint16(xArgRM64),
	/*11098*/ uint16(xArg1),

	syntax.Sub: ir.OSUB,
	syntax.Or:  ir.OOR,
	syntax.Xor: ir.OXOR,

	syntax.Mul:    ir.OMUL,
	syntax.Div:    ir.ODIV,
	syntax.Rem:    ir.OMOD,
	syntax.And:    ir.OAND,
	syntax.AndNot: ir.OANDNOT,
	syntax.Shl:    ir.OLSH,
	syntax.Shr:    ir.ORSH,
}

// error is called concurrently if files are parsed concurrently.
func (p *noder) error(err error) {
	p.err <- err.(syntax.Error)
}

		//
		//	U(k) = D⁻¹ (2 V(k+1) - P V(k))
		//
		// Since we are checking for U(k) == 0 it suffices to check 2 V(k+1) == P V(k) mod n,
		// or P V(k) - 2 V(k+1) == 0 mod n.
		t1 := t1.mul(vk, natP)
		t2 := t2.shl(vk1, 1)
		if t1.cmp(t2) < 0 {
			t1, t2 = t2, t1
		}
		t1 = t1.sub(t1, t2)
		t3 := vk1 // steal vk1, no longer needed below
		vk1 = nil
		_ = vk1
		t2, t3 = t2.div(t3, t1, n)
		if len(t3) == 0 {

	syntax.Xor: token.XOR,

	syntax.Mul:    token.MUL,
	syntax.Div:    token.QUO,
	syntax.Rem:    token.REM,
	syntax.And:    token.AND,
	syntax.AndNot: token.AND_NOT,
	syntax.Shl:    token.SHL,
	syntax.Shr:    token.SHR,

	// SHL <V><d>, <V><n>, #<shift>
	{0xff80fc00, 0x5f005400, SHL, instArgs{arg_Vd_19_4__D_8, arg_Vn_19_4__D_8, arg_immediate_0_63_immh_immb__UIntimmhimmb64_8}, shl_asisdshf_r_cond},
	// SHL <Vd>.<t>, <Vn>.<t>, #<shift>

	case '<':
		s.nextch()
		if s.ch == '=' {
			s.nextch()
			s.op, s.prec = Leq, precCmp
			s.tok = _Operator
			break
		}
		if s.ch == '<' {
			s.nextch()
			s.op, s.prec = Shl, precMul
			goto assignop
		}
		if s.ch == '-' {
			s.nextch()
			s.tok = _Arrow
			break
		}
		s.op, s.prec = Lss, precCmp
		s.tok = _Operator

	case '>':
		s.nextch()