November 3rd, 2002, 01:14 PM
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Contributing User
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Join Date: Jul 2002
Posts: 32
Time spent in forums: < 1 sec
Reputation Power: 11
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Help with my bit extraction code
Hello,
I recently wrote an algorithm that will extract (or atleast try to) X number of bits from a buffer. But, for some reason it doesn't seem to work all the time. For example, it can extract the bits the first time I run my algorithm, but not after that...I figure it's a problem with the way I am storing the bits in my buffer.
Just for your reference:
Code:
#define S8 signed char
#define S16 signed short
#define S32 signed int
#define U8 unsigned char
#define U16 unsigned short
#define U32 unsigned int
Now, here is my algorith expressed in C:
Code:
U32 U32SomeFunction(U16 U16Bits)
{
U32 U32Return;
while(true)
{
S32 S32BitsNeeded = U16Bits - m_U32BitBufferSize;
if(S32BitsNeeded > 0) /* Need to append more bits to buffer */
{
m_U32BitBufferSize += 8; /* Increase buffer size */
m_U32BitBuffer <<= 8; /* Shift buffer over one byte */
m_U32BitBuffer |= U8GetByte(); /* append byte to buffer */
}
else /* Have enough bits in buffer, return bits */
{
U32Return = m_U32BitBuffer >> (m_U32BitBufferSize - U16Bits); /* Save bits for return */
m_U32BitBufferSize -= U16Bits; /* Save new buffer size */
m_U32BitBuffer << (32 - m_U32BitBufferSize); /* Get rid of old bits */
m_U32BitBuffer >> (32 - m_U32BitBufferSize); /* Shift back right, padding 0's to the left */
return U32Return;
}
}
}
Any help would be great.
Thanks,
John
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