What version of Go are you using (go version)?

$ go version : 1.12

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

$ go env

What did you do?

type A struct {
ID int json:"id"
Amount float64 json:"amount"
}

ok case:
func main() {
var a = A{ID: 1, Amount: 7.11}
var b = A{ID: 2, Amount: 1.02}
c := A{ID: 1, Amount: 0.0000}
c.Amount = a.Amount + b.Amount
fmt.Printf("%f==%+v\n", c.Amount, c)
content, err := json.Marshal(c)
fmt.Println(string(content), err)
}
output:
8.130000=={ID:1 Amount:8.13}
{"id":1,"amount":8.13}

nok case :

func main() {
var a = A{ID: 1, Amount: 8.11}
var b = A{ID: 2, Amount: 1.02}
c := A{ID: 1, Amount: 0.0000}
c.Amount = a.Amount + b.Amount
fmt.Printf("%f==%+v\n", c.Amount, c)
content, err := json.Marshal(c)
fmt.Println(string(content), err)
}
output:
9.130000=={ID:1 Amount:9.129999999999999}
{"id":1,"amount":9.129999999999999}

What did you expect to see?

9.130000=={ID:1 Amount:9.13}
{"id":1,"amount":9.13}

What did you see instead?

9.130000=={ID:1 Amount:9.129999999999999}
{"id":1,"amount":9.129999999999999}

the boundary is 8, can any explain is this a feature or bug,if feature, why? any advice to avoid the case or solution?