{12999999, 4, "12990000", "13000000", "13000000"},
	} {
		x := nat(nil).setUint64(test.x)

		var d decimal
		d.init(x, 0)
		d.roundDown(test.n)
		if got := d.String(); got != test.down {
			t.Errorf("roundDown(%d, %d) = %s; want %s", test.x, test.n, got, test.down)
		}

		d.init(x, 0)
		d.round(test.n)
		if got := d.String(); got != test.even {

}

func TestDecimalRound(t *testing.T) {
	for i := 0; i < len(roundtests); i++ {
		test := &roundtests[i]
		d := NewDecimal(test.i)
		d.RoundDown(test.nd)
		s := d.String()
		if s != test.down {
			t.Errorf("Decimal %v RoundDown %d = %v, want %v",
				test.i, test.nd, s, test.down)
		}
		d = NewDecimal(test.i)
		d.Round(test.nd)
		s = d.String()
		if s != test.round {

// If n < 0, x remains unchanged.
func (x *decimal) round(n int) {
	if n < 0 || n >= len(x.mant) {
		return // nothing to do
	}

	if shouldRoundUp(x, n) {
		x.roundUp(n)
	} else {
		x.roundDown(n)
	}
}

func (x *decimal) roundUp(n int) {
	if n < 0 || n >= len(x.mant) {
		return // nothing to do
	}
	// 0 <= n < len(x.mant)

	// find first digit < '9'

// 0.09 -> 0.1.
func (a *decimal) Round(nd int) {
	if nd < 0 || nd >= a.nd {
		return
	}
	if shouldRoundUp(a, nd) {
		a.RoundUp(nd)
	} else {
		a.RoundDown(nd)
	}
}

// Round a down to nd digits (or fewer).
func (a *decimal) RoundDown(nd int) {
	if nd < 0 || nd >= a.nd {
		return
	}
	a.nd = nd
	trim(a)
}

// Round a up to nd digits (or fewer).
func (a *decimal) RoundUp(nd int) {

		// If it's okay to do either, then round to the nearest one.
		// If it's okay to do only one, do it.
		switch {
		case okdown && okup:
			d.round(i + 1)
			return
		case okdown:
			d.roundDown(i + 1)
			return
		case okup:
			d.roundUp(i + 1)
			return
		}
	}
}

// %e: d.ddddde±dd
func fmtE(buf []byte, fmt byte, prec int, d decimal) []byte {
	// first digit
	ch := byte('0')

		// If it's okay to do either, then round to the nearest one.
		// If it's okay to do only one, do it.
		switch {
		case okdown && okup:
			d.Round(mi + 1)
			return
		case okdown:
			d.RoundDown(mi + 1)
			return
		case okup:
			d.RoundUp(mi + 1)
			return
		}
	}
}

type decimalSlice struct {
	d      []byte
	nd, dp int
}

// %e: -d.ddddde±dd