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bits operation

I would like to know how I can extract some data from a byte array.
For example let's say I have a byte array with 4 elements ie 32 bits.
BYTE buf[4];

I fill buf with the following values : 00011{100 1}1110101 10100101
00000001.

Now I want to get the values between bracket.
How can I do that ?
Is Bitset appropriate knowing that in reality my array is 29 bytes long
and I want to extract 1-32 bits from a defined offset.
Jul 23 '05 #1
3 1659
"Vince" <vs**@caramail. com> wrote in message
news:42******** *************** @news.free.fr.. .
I would like to know how I can extract some data from a byte array.
For example let's say I have a byte array with 4 elements ie 32 bits.

BYTE buf[4];

I fill buf with the following values : 00011{100 1}1110101 10100101
00000001.

Now I want to get the values between bracket.
How can I do that ? With something like: ((buf[0]&7)<<1) | ((buf[0]>>7)&1)
(but it depends how you store the bits into the byte array).
Is Bitset appropriate knowing that in reality my array is 29 bytes long
and I want to extract 1-32 bits from a defined offset.

Yes, on a 32-bit platform, with bitset you should be able to easily
extract bits using something like:
(myBitSet>>bitO ffset).to_ulong () & ((1UL<<numBits)-1);
(NB: you need to special-case the case where numBits is 32!)
hth -Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form
Jul 23 '05 #2
raj
> BYTE buf[4];

I fill buf with the following values : 00011{100 1}1110101 10100101
00000001.

Now I want to get the values between bracket.
How can I do that ?


You could do that with ">>" , "<<" operators

Raj
Jul 23 '05 #3
Vince wrote:

I would like to know how I can extract some data from a byte array.
For example let's say I have a byte array with 4 elements ie 32 bits.
BYTE buf[4];

I fill buf with the following values : 00011{100 1}1110101 10100101
00000001.

Now I want to get the values between bracket.
How can I do that ?
Is Bitset appropriate knowing that in reality my array is 29 bytes long
and I want to extract 1-32 bits from a defined offset.

You will use two bitsets where you will assign buf[0] and buf[1] and get
the individual bits you want.

--
Ioannis Vranos

http://www23.brinkster.com/noicys
Jul 23 '05 #4

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