func (p *exporter) fraction(x constant.Value) {
sign := constant.Sign(x)
p.int(sign)
if sign == 0 {
return
}
p.ufloat(constant.Num(x))
p.ufloat(constant.Denom(x))
}
// floatString returns the string representation for a
// numeric value v in normalized floating-point format.
func floatString(v exact.Value) string {
if exact.Sign(v) == 0 {
return "0.0"
}
// x != 0
// convert |v| into a big.Rat x
x := new(big.Rat).SetFrac(absInt(exact.Num(v)), absInt(exact.Denom(v)))
// normalize x and determine exponent e
// (This is not very efficient, but also not speed-critical.)
var e int
for x.Cmp(ten) >= 0 {
x.Quo(x, ten)
e++
}
for x.Cmp(one) < 0 {
x.Mul(x, ten)
e--
}
// TODO(gri) Values such as 1/2 are easier to read in form 0.5
// rather than 5.0e-1. Similarly, 1.0e1 is easier to read as
// 10.0. Fine-tune best exponent range for readability.
s := x.FloatString(100) // good-enough precision
// trim trailing 0's
i := len(s)
for i > 0 && s[i-1] == '0' {
i--
}
s = s[:i]
// add a 0 if the number ends in decimal point
if len(s) > 0 && s[len(s)-1] == '.' {
s += "0"
}
// add exponent and sign
if e != 0 {
s += fmt.Sprintf("e%+d", e)
}
if exact.Sign(v) < 0 {
s = "-" + s
}
// TODO(gri) If v is a "small" fraction (i.e., numerator and denominator
// are just a small number of decimal digits), add the exact fraction as
// a comment. For instance: 3.3333...e-1 /* = 1/3 */
return s
}
func (p *exporter) float(x constant.Value) {
if x.Kind() != constant.Float {
log.Fatalf("gcimporter: unexpected constant %v, want float", x)
}
// extract sign (there is no -0)
sign := constant.Sign(x)
if sign == 0 {
// x == 0
p.int(0)
return
}
// x != 0
var f big.Float
if v, exact := constant.Float64Val(x); exact {
// float64
f.SetFloat64(v)
} else if num, denom := constant.Num(x), constant.Denom(x); num.Kind() == constant.Int {
// TODO(gri): add big.Rat accessor to constant.Value.
r := valueToRat(num)
f.SetRat(r.Quo(r, valueToRat(denom)))
} else {
// Value too large to represent as a fraction => inaccessible.
// TODO(gri): add big.Float accessor to constant.Value.
f.SetFloat64(math.MaxFloat64) // FIXME
}
// extract exponent such that 0.5 <= m < 1.0
var m big.Float
exp := f.MantExp(&m)
// extract mantissa as *big.Int
// - set exponent large enough so mant satisfies mant.IsInt()
// - get *big.Int from mant
m.SetMantExp(&m, int(m.MinPrec()))
mant, acc := m.Int(nil)
if acc != big.Exact {
log.Fatalf("gcimporter: internal error")
}
p.int(sign)
p.int(exp)
p.string(string(mant.Bytes()))
}