How to display float number nicely in go

Question

I want to be able to display very large floating point numbers created with math/big.

• if there are no decimals, no .000 should be added
• only add the necessary number of decimals (display 1.1234 not 1.123400)
• great precision (tens of exact decimals)

https://play.golang.org/p/CulS5wXxzGq

coef := new(big.Float).SetPrec(4096)
coef.SetString("1000000000000000")
a := new(big.Float).SetPrec(4096)
a.SetString("1")
a.Quo(a, coef)
fmt.Printf("%.100g\n", a)
// 1e-15
// was expecting: 0.000000000000001

b := new(big.Float).SetPrec(4096)
b.SetString("1234.00")
fmt.Printf("%.100g\n", b)
// 1234.00
// looks good

c := new(big.Float).SetPrec(4096)
c.SetString("1234.001000")
fmt.Printf("%.100g\n", c)
// 1234.001000
// looks good

Answer 1

There is a Text() method for big.Float that I think does what you want. If passed a negative precision, it will use as many digits as necessary to represent the value, but no more. Try:

func format(x *big.Float) string {
    return x.Text('f', -1)
}

That will give you:

0.000000000000001
1234
1234.001