Nrthugu

How can a negative integer be represented as a binary in Go, using the two's complement notation?

For example:

n := int64(-1)

fmt.Printf("%b", n)

fmt.Println(strconv.FormatInt(n, 2))

Both lines print -1. The result shoud be like ffffffffffffffff.

I am sorry but did you mean you wanted to explore how int64 values are stored in the memory? You will need to use the unsafe package to force reinterpret a value in go.

This code does what you want:

package main



import (

    "fmt"

    "unsafe"

)



func main() {

    a := int64(-1)

    fmt.Printf("%xn", *(*[8]byte)(unsafe.Pointer(&a)))

}

I also wrote a func to programmatically calculate the two's complement notation of a int64 in case that you just wanted to calculate the value:

package main



import (

    "fmt"

    "math/big"

)



func main() {

    a := int64(-1)

    fmt.Printf("%xn", TwoComplement(a))

}



func TwoComplement(val int64) byte {

    n := big.NewInt(val)



    var r byte

    if n.Cmp(big.NewInt(0)) != -1 {

        r = n.Bytes()

    } else {

        mask := big.NewInt(1)

        mask.Lsh(mask, 64)



        r = n.Add(n, mask).Bytes()

    }



    res := bytes.NewBuffer(byte{})

    for i := 0; i < 8-len(r); i++ {

        res.WriteByte(0)

    }

    res.Write(r)

    return res.Bytes()

}