// amd64:"SHRQ.*,.*,"
	shr := x>>s | y<<ŝ
	// amd64:"SHLQ.*,.*,"
	shl := x<<s | y>>ŝ
	return shr, shl
}

func checkShiftToMask(u []uint64, s []int64) {
	// amd64:-"SHR",-"SHL","ANDQ"
	u[0] = u[0] >> 5 << 5
	// amd64:-"SAR",-"SHL","ANDQ"
	s[0] = s[0] >> 5 << 5
	// amd64:-"SHR",-"SHL","ANDQ"
	u[1] = u[1] << 5 >> 5

		return z[:0]
	}
	// m > 0

	n := m + int(s/_W)
	z = z.make(n + 1)
	z[n] = shlVU(z[n-m:n], x, s%_W)
	clear(z[0 : n-m])

	return z.norm()
}

// z = x >> s
func (z nat) shr(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)
	n := m - int(s/_W)
	if n <= 0 {
		return z[:0]

	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,

		x.expr = e
		check.overflow(x, x.Pos())
		return
	}

	x.mode = value
	// x.typ remains unchanged
}

func isShift(op token.Token) bool {
	return op == token.SHL || op == token.SHR
}

func isComparison(op token.Token) bool {
	// Note: tokens are not ordered well to make this much easier
	switch op {
	case token.EQL, token.NEQ, token.LSS, token.LEQ, token.GTR, token.GEQ:
		return true

			z = new(Int)
		}
		z.neg = x.neg
		switch {
		case exp > allBits:
			z.abs = z.abs.shl(x.mant, exp-allBits)
		default:
			z.abs = z.abs.set(x.mant)
		case exp < allBits:
			z.abs = z.abs.shr(x.mant, allBits-exp)
		}
		return z, acc

	case zero:
		return z.SetInt64(0), Exact

	case inf:
		return nil, makeAcc(x.neg)
	}

	panic("unreachable")
}