Copy bits of Byte array to Int32

[Lance]

I have an array of bytes that I need to convert into an
array of Integers. But, the number of bits per value in
the Byte array is not necessarily divisible by 8 (although
it will never exceed 32).

For example, lets say I have a an array of bytes
(byteValues) that represents a string of 7 bit values. In
this case, the first value would be stored in the first 7
bits of byteValues(0), the second value would be stored in
the last bit of byteValues(0) and the first 6 bits of
byteValues(1), etc.

So, I need a method that will copy bits from byteValues to
an Integer and allows me to specify the offset (in bits)
and the number of bits to copy. I thought there was a
method that would do this type of thing, but now I can't
find it.

Thanks for any help!
Lance

[Tom Shelton]

In article <03****************************@phx.gbl>, Lance wrote:

I have an array of bytes that I need to convert into an
array of Integers. But, the number of bits per value in
the Byte array is not necessarily divisible by 8 (although
it will never exceed 32).

For example, lets say I have a an array of bytes
(byteValues) that represents a string of 7 bit values. In
this case, the first value would be stored in the first 7
bits of byteValues(0), the second value would be stored in
the last bit of byteValues(0) and the first 6 bits of
byteValues(1), etc.

So, I need a method that will copy bits from byteValues to
an Integer and allows me to specify the offset (in bits)
and the number of bits to copy. I thought there was a
method that would do this type of thing, but now I can't
find it.

Thanks for any help!
Lance

Would System.BitConverter help?

--
Tom Shelton
MVP [Visual Basic]

[Jackson Davis [MSFT]]

-----Original Message-----
I have an array of bytes that I need to convert into an
array of Integers. But, the number of bits per value in
the Byte array is not necessarily divisible by 8 (althoughit will never exceed 32).

For example, lets say I have a an array of bytes
(byteValues) that represents a string of 7 bit values. Inthis case, the first value would be stored in the first 7
bits of byteValues(0), the second value would be stored inthe last bit of byteValues(0) and the first 6 bits of
byteValues(1), etc.

So, I need a method that will copy bits from byteValues toan Integer and allows me to specify the offset (in bits)
and the number of bits to copy. I thought there was a
method that would do this type of thing, but now I can't
find it.

Thanks for any help!
Lance
.

Lance,

I have never seen a method that doeswhat you ask, but it
would not be too hard to write the method yourself using
bit masks. Here is a function I wrote in C# that takes an
integer value and the starting and ending bit, and
extracts the sub-integer. (I didn't test it too deeply,
but it seems to work). You can use this to write a class
that keeps track of where you are in your array and what
bit offsets you are at.

// returns an sub-integer contained in an integer
// given the first bit number and the second bit number
// for instance, if val is the binary number: 0010
// firstBit is 1, and secondBit is 2,
// this returns the binary number 0010.
// if first bit it 2 and secondBit is 4 then this returns
// the binary number 0001
public static int GetNumber(int val, int firstBit, int
secondBit)
{
int mask = 0;

if (firstBit < 1 || firstBit > 32 ||
secondBit < 1 || secondBit > 32)
{
throw new System.ArgumentException();
}
if (secondBit < firstBit)
{
throw new System.ArgumentException();
}

for (int i = 0; i < secondBit; i++)
{
mask = mask << 1;
mask++;
}

mask = mask << (firstBit - 1);

val = val & mask;
val = val >> (firstBit - 1);

return val;
}

Hope that helps get you in the right direction.

Jackson Davis [MSFT]
--
This posting is provided "AS IS" with no warranties, and
confers no rights
Samples are subject to the terms specified at
http://www.microsoft.com/info/cpyright.htm

[Jackson Davis [MSFT]]

-----Original Message-----

-----Original Message-----
I have an array of bytes that I need to convert into an
array of Integers. But, the number of bits per value in
the Byte array is not necessarily divisible by 8(although

it will never exceed 32).

For example, lets say I have a an array of bytes
(byteValues) that represents a string of 7 bit values.

In

this case, the first value would be stored in the first 7bits of byteValues(0), the second value would be stored

in

the last bit of byteValues(0) and the first 6 bits of
byteValues(1), etc.

So, I need a method that will copy bits from byteValues

to

an Integer and allows me to specify the offset (in bits)
and the number of bits to copy. I thought there was a
method that would do this type of thing, but now I can't
find it.

Thanks for any help!
Lance
.

Lance,

I have never seen a method that doeswhat you ask, but it
would not be too hard to write the method yourself using
bit masks. Here is a function I wrote in C# that takes an
integer value and the starting and ending bit, and
extracts the sub-integer. (I didn't test it too deeply,
but it seems to work). You can use this to write a class
that keeps track of where you are in your array and what
bit offsets you are at.

// returns an sub-integer contained in an integer
// given the first bit number and the second bit number
// for instance, if val is the binary number: 0010
// firstBit is 1, and secondBit is 2,
// this returns the binary number 0010.
// if first bit it 2 and secondBit is 4 then this returns
// the binary number 0001
public static int GetNumber(int val, int firstBit, int
secondBit)
{
int mask = 0;

if (firstBit < 1 || firstBit > 32 ||
secondBit < 1 || secondBit > 32)
{
throw new System.ArgumentException();
}
if (secondBit < firstBit)
{
throw new System.ArgumentException();
}

for (int i = 0; i < secondBit; i++)
{
mask = mask << 1;
mask++;
}

mask = mask << (firstBit - 1);

val = val & mask;
val = val >> (firstBit - 1);

return val;
}

Hope that helps get you in the right direction.

Jackson Davis [MSFT]
--
This posting is provided "AS IS" with no warranties, and
confers no rights
Samples are subject to the terms specified at
http://www.microsoft.com/info/cpyright.htm

.

Yes, it appears System.BitConverter will do the same thing
as I did above.
Jackson Davis [MSFT]--
This posting is provided "AS IS" with no warranties, and
confers no rights
Samples are subject to the terms specified at
http://www.microsoft.com/info/cpyright.htm

[Jay B. Harlow [MVP - Outlook]]

Lance,
In addition to the others comments. You can use System.Buffer to copy a byte
array to an integer array. However the array needs to be the correct size.

My concern with both System.Buffer & System.BitConverter is that they use
the full 8 bits of a byte, where as you have only 7 bits of a byte.

You could possible do either a pre process on the byte array or a post
process on the integer array to get a full 8 bits in a byte...

Not sure if System.Collections.BitArray would help with getting the required
bits needed out or not.

Hope this helps
Jay

"Lance" <zi***@hotmail.com> wrote in message
news:03****************************@phx.gbl...

I have an array of bytes that I need to convert into an
array of Integers. But, the number of bits per value in
the Byte array is not necessarily divisible by 8 (although
it will never exceed 32).

For example, lets say I have a an array of bytes
(byteValues) that represents a string of 7 bit values. In
this case, the first value would be stored in the first 7
bits of byteValues(0), the second value would be stored in
the last bit of byteValues(0) and the first 6 bits of
byteValues(1), etc.

So, I need a method that will copy bits from byteValues to
an Integer and allows me to specify the offset (in bits)
and the number of bits to copy. I thought there was a
method that would do this type of thing, but now I can't
find it.

Thanks for any help!
Lance