Question

I need to convert a string to 7-bit ASCII with even parity in a C# application which communicates with a mainframe. I tried using Encoding.ASCII, however, it does not have the correct parity.

Answer 1

Perhaps something like this:

public static byte[] StringTo7bitAsciiEvenParity(string text)
{
    byte[] bytes = Encoding.ASCII.GetBytes(text);

    for(int i = 0; i < bytes.Length; i++)
    {
        if(((((bytes[i] * 0x0101010101010101UL) & 0x8040201008040201UL) % 0x1FF) & 1) == 0)
        {
            bytes[i] &= 0x7F;
        }
        else
        {
            bytes[i] |= 0x80;
        }
    }
    return bytes;
}

Completely untested. Don’t ask me how the magic to compute parity works. I just found it here. But some variant of this should do what you want.

I tried to make this work for the case ',' becoming 0x82. But I can’t work out how that is supposed to be done. ',' is, in ASCII, binary 00101100 and 0x82 is binary 10000010. I don’t see the correlation at all.