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Converting long to byte array and back

Posted on 2013-11-05
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Last Modified: 2013-11-07
I need to convert a long to a byte array and back again. I can't use BitConverter since the Micro Framework version of C# doesn't support it. Here's the code I'm using:
            long origLong = long.MinValue;
            byte[] bytes = new byte[8];
            for (int i = 0; i < 8; i++) {
                bytes[i] = (byte)(origLong >> (i * 8) & 0xFF);
            }
            long newLong = 0;
            for (int i = 0; i < 8; i++) {
                newLong = newLong | (long)(bytes[i] << (i * 8));
            }
            for (int i = 0; i < bytes.Length; i++) {
                Debug.Write(bytes[i] + " ");
            }
            Debug.Print("");
            Debug.Print("orig: " + origLong + ", new: " + newLong);

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The results in the Output are:
0 0 0 0 0 0 0 128 
orig: -9223372036854775808, new: -2147483648

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It looks like the conversion to a byte array is good but the conversion back to long is not. Also, on the statement with the OR operator (#8), I get the warning "Bitwise-or operator used on a sign-extended operand; consider casting to a smaller unsigned type first".

How can I do this?
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Question by:BlearyEye
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4 Comments
 
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Accepted Solution

by:
anarki_jimbel earned 500 total points
ID: 39626239
The problem exists because of a wrong casting order in the line 8. Cast a byte to long before shifting, change to:

newLong = newLong | ((long)bytes[i] << (i * 8));

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Author Closing Comment

by:BlearyEye
ID: 39627401
Perfect, thanks.
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Author Comment

by:BlearyEye
ID: 39630554
As a follow-up, I've come across two implementations of BitConverter for MF:

https://bitbucket.org/aalmada/hydramf/src/779d1c524a9c/HydraMF.Hardware/BitConverter.cs
http://forums.netduino.com/index.php?/topic/308-bitconverter/, and accompanying comments (there are bugs in the posted code).
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Expert Comment

by:anarki_jimbel
ID: 39631282
Thanks, interesting!
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