Help converting a function

[leogazio (Leonardo Gazio)]

Hi. Could anyone help me converting this Java function to GO?

public long complementOfTo(String hex){
        
        HexToBin hextobin = new HexToBin();
        long coord = 0;
        int a = Integer.parseInt(String.valueOf(hextobin.hexToBin(hex).charAt(0)));
        switch (a){
            case 0:
                coord = Long.parseLong(hex,16);
                break;
            case 1:
                long c = Long.parseLong(hex,16);
                long r = c ^ (long)(Math.pow(2, Math.ceil(Math.log(c)/Math.log(2))) -1);
                coord = Long.parseLong("-".concat(String.valueOf(r)));
                break;
        }
        return coord;
}

Any help is appreciated. Tnx.

[christophberger]

Most of this function should be rather straightforward to convert if you know Go. At which part of the code did you get stuck?

[johandalabacka (Johan Dahl)]

@leogazio

coord = Long.parseLong(“-”.concat(String.valueOf( r )));

Interesting line converting a number to a string and then back to a negative integer

The switch case takes the first character of the conversion of the hex to bin and converts it to a integer you could really just switch on the first character instead.

HexToBin() converts a hexadecimal number to a binary and if the first digit is a zero I guess it pads it to a certain width. How many digits?

I may be mistaken but the thing the function does is to convert a hexadecimal number in a string into a two’s complement number (most common representation of signed integers on computers)

package main

import (
	"fmt"
	"strconv"
)

func complementOfTwo(hex string) int64 {
	coord, _ := strconv.ParseUint(hex, 16, 64)
	return (int64)(coord)
}

func main() {
	fmt.Println(complementOfTwo("0000000000000001")) //  1
	fmt.Println(complementOfTwo("ffffffffffffffff")) //  -1
}