Exemplo n.º 1
0
Arquivo: mparith3.go Projeto: rsc/tmp
func Fconv(fvp *Mpflt, flag int) string {
	if flag&obj.FmtSharp == 0 {
		return fvp.Val.Format('b', 0)
	}

	// use decimal format for error messages

	// determine sign
	f := &fvp.Val
	var sign string
	if fvp.Val.Signbit() {
		sign = "-"
		f = new(big.Float).Abs(f)
	} else if flag&obj.FmtSign != 0 {
		sign = "+"
	}

	// Use fmt formatting if in float64 range (common case).
	if x, _ := f.Float64(); !math.IsInf(x, 0) {
		return fmt.Sprintf("%s%.6g", sign, x)
	}

	// Out of float64 range. Do approximate manual to decimal
	// conversion to avoid precise but possibly slow Float
	// formatting. The exponent is > 0 since a negative out-
	// of-range exponent would have underflowed and led to 0.
	// f = mant * 2**exp
	var mant big.Float
	exp := float64(f.MantExp(&mant)) // 0.5 <= mant < 1.0, exp > 0

	// approximate float64 mantissa m and decimal exponent d
	// f ~ m * 10**d
	m, _ := mant.Float64()            // 0.5 <= m < 1.0
	d := exp * (math.Ln2 / math.Ln10) // log_10(2)

	// adjust m for truncated (integer) decimal exponent e
	e := int64(d)
	m *= math.Pow(10, d-float64(e))
	for m >= 10 {
		m /= 10
		e++
	}

	return fmt.Sprintf("%s%.5fe+%d", sign, m, e)
}
Exemplo n.º 2
0
Arquivo: mparith2.go Projeto: rsc/tmp
func mpmovefltfix(a *Mpint, b *Mpflt) int {
	if _, acc := b.Val.Int(&a.Val); acc == big.Exact {
		return 0
	}

	const delta = 16 // a reasonably small number of bits > 0
	var t big.Float
	t.SetPrec(Mpprec - delta)

	// try rounding down a little
	t.SetMode(big.ToZero)
	t.Set(&b.Val)
	if _, acc := t.Int(&a.Val); acc == big.Exact {
		return 0
	}

	// try rounding up a little
	t.SetMode(big.AwayFromZero)
	t.Set(&b.Val)
	if _, acc := t.Int(&a.Val); acc == big.Exact {
		return 0
	}

	return -1
}