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)
}
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
}
