Question

I have the following function to get an int from a high-byte and a low-byte:

public static int FromBytes(byte high, byte low)
{
    return high * (byte.MaxValue + 1) + low;
}

When I analyze the assembly with FxCop, I get the following critical warning:

CA2233: OperationsShouldNotOverflow
Arithmetic operations should not be
done without first validating the
operands to prevent overflow.

I can’t see how this could possibly overflow, so I am just assuming FxCop is being overzealous.
Am I missing something? And what steps could be taken to correct what I have (or at least make the FxCop warning go away!)?

Answer 1

As Daniel A. White pointed out, you get the message because “(byte.MaxValue + 1)” overflows a byte.

But instead of casting and multiplying, I would simply shift the bits as done in the code below:

public static int FromBytes(byte high, byte low) {
    return high << 8 | low;
}

As a side effect, this code will probably perform better. I haven’t checked the resulting IL or x86 to see if the compiler and/or the JITter are smart enough to optimize the original expression.