How to apply the two add-on to an Hex string in c#?

Question

I need help converting an Hex string into an Hex string by applying two add-on.

Example: 0x00FEB5AB 0x00014A55

My Hex. 00FF17DB ? (represents a negative latitude)

and 00FCFF75 ? (represents a negative longitude)

Thank you all.

Answer 1

A simple way may be to calculate the complement to 1 and add 1 as described in the entry Complement to two wikipedia.

I say it’s a simple way because it’s easy to calculate the complement of 1, just for this to apply the operation bitwise NOT at value:

const string valor = "00FEB5AB";
//Converte para inteiro
uint valorInteiro = Convert.ToUInt32(valor, 16);
//Aplica o bitwise NOT e soma 1
uint complemento = ~valorInteiro + 1;
//Converte para string no formato hexadecimal
string complementoHex = string.Format("{0:X}", complemento);

Note that the calculated value is "FF014A55" and not "00014A55" as you say, because the result is calculated considering the amplitude (number of bytes) of the input.

By what I was given to realize the calculators existing on the net only consider the bytes significant, making the calculation truncating the non-significant bytes (00’s left).

Using the above code, the following method allows the calculation of the two forms:

public string ComputeTwosComplement(string hexValue, bool areAllBytesSignificant)
{
    const int maxNumberOfBytes = 8;
    int lenght = hexValue.Length;

    //Não permite mais de 64bits
    if (lenght > maxNumberOfBytes*2) throw new ArgumentOutOfRangeException(hexValue);

    //Converte hexadecimal para long
    ulong intValue = Convert.ToUInt64(hexValue, 16);

    //Calcula o complemento para 2
    ulong complement = (~intValue + 1);

    //Converte para hexadecimal
    string twosComplement = string.Format("{0:X16}", complement);

    if (areAllBytesSignificant)
    {
        //Ajusta para o mesmo número de bytes do valor passado
        twosComplement = twosComplement.Substring(maxNumberOfBytes*2 - lenght);
    }
    else
    {
        //Representação hexadecimal do valor passado sem 00's à esquerda
        string significantBytes = string.Format("{0:X}", intValue);
        //Ajusta para o número de bytes significativos do valor passado
        twosComplement = twosComplement.Substring(maxNumberOfBytes*2 - significantBytes.Length);
    }
    return twosComplement;
}

To maintain amplitude and get "FF014A55" use:

ComputeTwosComplement("00FEB5AB", true);

To adjust the amplitude and get "014A55" use:

ComputeTwosComplement("00FEB5AB", false);

Note that if the value passed does not have 00’s on the left ("FEB5AB") it is indifferent to pass true or false, the result is always "014A55".