How can I extract datetime from the following bytes?

Question

I have the following 5 bytes in the attached image and need to extract the datetime from it. I understand I'll need to bit shift and maybe use bitwise and's, but fail to get the correct information from the bytes.

Can you explain more about how the two `Y` are calculated. Are they a single value with bits concationated or is each one represent a single digit of the last two digits of a year? The fact that they are separated from each other makes me think each is a digit, but you can only represent 0-7 with the 3 bits it uses in `Byte 3`. If they are concatenated that gives you 0-127, so you could use that for 0-99 — Scott Chamberlain, Dec 17 '15 at 21:57
4 bytes = ((Y>>4)<<29) + (Day<<24) + (Hour<<19) + (Minute<<13) + (Seconds<<7) + Hundredths — Matthew Lamb, Dec 17 '15 at 22:06
Y = Year – 1993. If the top three bits of byte 3 are used, this is valid to 2120. If not, it will roll over after 2008. — Matthew Lamb, Dec 17 '15 at 22:06

score 3 · Accepted Answer · answered Dec 17 '15 at 22:13

3

Maybe this?

int yearBase = 1993;

int year = yearBase + (int) ((bytes[4] & 0xF0) >> 4) | ((bytes[3] & 0xE0) >> 1);
int month = (int) (bytes[4] & 0x0F);
int day = (int) (bytes[3] & 0x1F);
int hour = (int) ((bytes[2] & 0xF8) >> 3);
int min = (int) (((bytes[2] & 0x03) << 3) | ((bytes[1] & 0xE0) >> 5));
int sec = (int) ((bytes[1] & 0x1F) << 1) | ((bytes[0] & 0x80) >> 7);
int hundreths = (int) (bytes[0] & 0x7F);

answered Dec 17 '15 at 22:13

Matthew Watson

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Matt that is given me some good dates, I'll have to test this against the dates that I know. I'll have to track down some data for that, but the above is definitely on the right track, Thank you. – Matthew Lamb Dec 17 '15 at 22:34

score 1 · Answer 2 · edited May 23 '17 at 12:16

I recently answer a question about bitshifting and integer packing in C#.

May be helper class written in that case can be usefull to you as starting point

public static class BinaryConverter
{
    public static BitArray ToBinary(this int numeral)
    {
        return new BitArray(new[] { numeral });
    }

    public static int ToNumeral(this BitArray binary)
    {
        if (binary == null)
            throw new ArgumentNullException("binary");
        if (binary.Length > 32)
            throw new ArgumentException("must be at most 32 bits long");

        var result = new int[1];
        binary.CopyTo(result, 0);
        return result[0];
    }

    public static BitArray Take (this BitArray current, int length )
    {
        if (current.Length < length)
            throw new Exception("Invalid length parameter");

        List<bool> taken = new List<bool>();

        for (int i = 0; i < length; i++)
                taken.Add(current.Get(i));

        return new BitArray(taken.ToArray());
    }

    public static BitArray Shift (this BitArray current, int length )
    {
        if (current.Length < length)
            throw new Exception("Invalid length parameter");

        List<bool> shifted = new List<bool>();

        for (int i = 0; i < current.Length - length; i++)
            shifted.Add(current.Get(length + i));

        return new BitArray(shifted.ToArray());
    }

    public static BitArray FitSize (this BitArray current, int size)
    {
        List<bool> bools = new List<bool>() ;
        bools = bools.InitBoolArray(size);

        for (int i = 0; i < current.Count; i++)
                bools[i] = current.Get(i) ;

        return new BitArray(bools.ToArray());
    }

    public static List<bool> InitBoolArray(this List<bool> current, int size)
    {
        List<bool> bools = new List<bool> ();

        for (int i = 0; i < size; i++)
            bools.Add(false);

        return bools ;
    }

Here the reference to that answer Dynamic Bit Shifting / Unshifting

At the link above is displayed how pack small number on the same integer, your five bytes is pretty close to that question

How can I extract datetime from the following bytes?

2 Answers2