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How to know the first bit of a data byte

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Brewling
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How to know the first bit of a data byte

Post by Brewling » Sun Jun 11, 2017 11:08 pm

When I receive an APDU command, I have to see the first bit of the first data byte,1 or 0.

Is there an easier way to see an specific bit from a byte in java card?

Thanks a lot for any help.
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Tazmania09
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Re: How to know the first bit of a data byte

Post by Tazmania09 » Mon Jun 12, 2017 4:01 am

You may try to use AND operation to know the bit value.

For example,
Make your data do the AND operation with 0x80.
So,
- if it is 1 in the first bit, the operation result will be 0x80.
- and if it is 0 in the first bit,the operation result will be 0.
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Brewling
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Re: How to know the first bit of a data byte

Post by Brewling » Mon Jun 12, 2017 4:42 am

Wow, that a good idea. Thanks Tazmania09. You saved my day. :lol:
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