binary question

[Deeko]

I'm fairly certain this is more of a math quesion than a programming question, that's why I'm posting this here.

I'm given an 8-bit error code by a device and each bit is a separate flag, so I need to parse them out. I know there is some operation to perform...bit shift or xor or something....but for the life of me I can't remember and google is no help. Anyone?

Thanks

 

[kranky]

Do a series of bitwise ANDs to extract each bit.

For example, to extract the value of the bit in the second position, do a bitwise AND with 00000010. If the result is decimal 2, the second bit was set.

 

[Deeko]

oh yea...duh...that works. thanks again.

 

[Descartes]

As kranky said, you're talking about bitwise operations. Some simply call it "bit twiddling" as well. Anyway, here are the basic "rules":

To test for a bit, you bitwise and it against a mask:

mask = 0x01
value = 1
if (value & mask == value) it's on

To set a bit:

mask = 0x01
value = 0
value |= mask

To toggle a bit (on if off, off if on):

mask = 0x01
value = 1
value ^= mask

To turn off a bit:

mask = 0x01
value = 1
value &= ~mask

That about covers everything you'd need to do for simple error code checking. The bitwise operators in the examples above are valid for most languages with a C-derived syntax.