예제 #1
0
파일: mparith3.go 프로젝트: danny8002/go
func Fconv(fvp *Mpflt, flag int) string {
	if flag&obj.FmtSharp == 0 {
		return fvp.Val.Text('b', 0)
	}

	// use decimal format for error messages

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

	// Don't try to convert infinities (will not terminate).
	if f.IsInf() {
		return sign + "Inf"
	}

	// Use exact fmt formatting if in float64 range (common case):
	// proceed if f doesn't underflow to 0 or overflow to inf.
	if x, _ := f.Float64(); f.Sign() == 0 == (x == 0) && !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.
	// f = mant * 2**exp
	var mant big.Float
	exp := f.MantExp(&mant) // 0.5 <= mant < 1.0

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

	// ensure 1 <= m < 10
	switch {
	case m < 1-0.5e-6:
		// The %.6g format below rounds m to 5 digits after the
		// decimal point. Make sure that m*10 < 10 even after
		// rounding up: m*10 + 0.5e-5 < 10 => m < 1 - 0.5e6.
		m *= 10
		e--
	case m >= 10:
		m /= 10
		e++
	}

	return fmt.Sprintf("%s%.6ge%+d", sign, m, e)
}
예제 #2
0
파일: mparith3.go 프로젝트: gmwu/go
func Fconv(fvp *Mpflt, flag int) string {
	if flag&obj.FmtSharp == 0 {
		return fvp.Val.Text('b', 0)
	}

	// use decimal format for error messages

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

	// Don't try to convert infinities (will not terminate).
	if f.IsInf() {
		return sign + "Inf"
	}

	// 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)
}