英文:
Negative big.Int turns positive after using Int64() conversion due integer overflow
问题
我有一个简单的if语句，用于比较两个数字。由于编译错误，我无法使用big.Int与零进行比较，因此我尝试将其转换为int64和float32。问题是，在调用Int64或float32(diff.Int64())之后，diff会被转换为一个正数，这可能是整数溢出的结果。如果有人能够向我展示如何安全地准备diff变量以与零进行比较，我将不胜感激。
package main
import (
"fmt"
"math/big"
)
func main() {
var amount1 = &big.Int{}
var amount2 = &big.Int{}
amount1.SetString("465673065724131968098", 10)
amount2.SetString("500000000000000000000", 10)
diff := big.NewInt(0).Sub(amount1, amount2)
fmt.Println(diff)
// -34326934275868031902 << 这是应该与0进行比较的正确数字
fmt.Println(diff.Int64())
// 2566553871551071330 << 这是if语句与0进行比较的结果
if diff.Int64() > 0 {
fmt.Println(float64(diff.Int64()), "大于0")
}
}
英文:
I have a simple if statement which compares two numbers. I couldn't use big.Int to compare with zero due to compile error, therefore I tried to convert to an int64 and to a float32. The problem is that after calling Int64 or float32(diff.Int64()), diff gets converted into a positive number which is a result of an integer overflow I suspect. I would appreciate if somebody could show me what is the safe way to prepare the diff variable for the comparison with zero.
package main
import (
"fmt"
"math/big"
)
func main() {
var amount1 = &big.Int{}
var amount2 = &big.Int{}
amount1.SetString("465673065724131968098", 10)
amount2.SetString("500000000000000000000", 10)
diff := big.NewInt(0).Sub(amount1, amount2)
fmt.Println(diff)
// -34326934275868031902 << this is the correct number which should be compared to 0
fmt.Println(diff.Int64())
// 2566553871551071330 << this is what the if statement compares to 0
if diff.Int64() > 0 {
fmt.Println(float64(diff.Int64()), "is bigger than 0")
}
}
答案1
得分: 2
使用Int.Cmp()将其与另一个表示为0的big.Int值进行比较。
例如：
zero := new(big.Int)
switch result := diff.Cmp(zero); result {
case -1:
fmt.Println(diff, "is less than", zero)
case 0:
fmt.Println(diff, "is", zero)
case 1:
fmt.Println(diff, "is greater than", zero)
}
这将输出：
-34326934275868031902 is less than 0
当与特殊的0进行比较时，你也可以使用Int.Sign()，它根据与0的比较结果返回-1、0、+1。
switch sign := diff.Sign(); sign {
case -1:
fmt.Println(diff, "is negative")
case 0:
fmt.Println(diff, "is 0")
case 1:
fmt.Println(diff, "is positive")
}
这将输出：
-34326934275868031902 is negative
在Go Playground上尝试这些示例。
参考资料：
英文:
Use Int.Cmp() to compare it to another big.Int value, one representing 0.
For example:
zero := new(big.Int)
switch result := diff.Cmp(zero); result {
case -1:
fmt.Println(diff, "is less than", zero)
case 0:
fmt.Println(diff, "is", zero)
case 1:
fmt.Println(diff, "is greater than", zero)
}
This will output:
-34326934275868031902 is less than 0
When comparing to the special 0, instead you could also use Int.Sign() which returns -1, 0, +1 depending on the result of the comparison to 0.
switch sign := diff.Sign(); sign {
case -1:
fmt.Println(diff, "is negative")
case 0:
fmt.Println(diff, "is 0")
case 1:
fmt.Println(diff, "is positive")
}
This will output:
-34326934275868031902 is negative
Try the examples on the Go Playground.
See related:
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