C#: Manual bit conversion?

Question

Is there a better way to write this than using BitConverter?

public static class ByteArrayExtensions
{

    public static int IntFromUInt24(this byte[] bytes)
    {
        if (bytes == null)
        {
            throw new ArgumentNullException();
        }

        if (bytes.Length != 3)
        {
            throw new ArgumentOutOfRangeException
                ("bytes", "Must have length of three.");
        }

        return BitConverter.ToInt32
                    (new byte[] { bytes[0], bytes[1], bytes[2], 0 }, 0);
    }

}

You could use the Bit Shift operator `<<` to move the values of bytes[0-2]. — davisoa, Oct 15 '10 at 21:55
http://stackoverflow.com/questions/3559183/reading-an-unsigned-24-bit-integer-from-a-c-stream — Alon Gubkin, Oct 15 '10 at 22:07

CodesInChaos · Answer 1 · 2010-10-15T22:00:12.430

3

I'd use:

return bytes[2]<<16|bytes[1]<<8|bytes[0];

Be careful with endianness: This code only works with little-endian 24 bit numbers.

BitConverter on the other hand uses native endianness. So your could wouldn't work at all big-endian systems.

edited Oct 15 '10 at 22:00

answered Oct 15 '10 at 21:54

CodesInChaos

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Although shifting might be faster (I don't know), `BitConverter` is more readable, so then it'd depend on what aspect "better" is focused on. – C.Evenhuis Oct 15 '10 at 21:56
1

If it were a 32 bit number I'd probably use BitConverter too. But since 24 bit numbers already require fiddling, BitConverter isn't more readable IMO. – CodesInChaos Oct 15 '10 at 21:59
If BitConverter uses native endianness, wouldn't BitConverter work on both big-endian and little-endian machines, while your answer would only work on little-endian machines? – GoHeavyOrGoHome Oct 15 '10 at 22:28
@GoHeavyOrGoHome: Given the same byte array, `BitConverter` will produce a different `int` depending on whether the platform is big- or little-endian, whereas this answer will produce the same `int` regardless of the platform's endianness. Which one you need will be determined by where your byte array comes from and how it's constructed. – LukeH Oct 15 '10 at 22:52
And even if the byte array contained a 24 bit int in native endianness his code wouldn't work. It would fill the upper three bytes of the int, and not the lower three. I think BitConverter isn't made for serialization but for interacting with native structs which are typed as a buffer(byte[]). – CodesInChaos Oct 15 '10 at 22:53

C#: Manual bit conversion?

1 Answers1