help me

This is a discussion on help me within the Networking/Device Communication forums, part of the General Programming Boards category; i need a bit stuffing example...

  1. #1
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    help me

    i need a bit stuffing example

  2. #2
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    In what context?

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    Mats
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  3. #3
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    i want to simulate bit stuffing in frames

    the flag is "01111110"

    and i must do bit stuffing after the 5th bit

    then un-stuffing it in the reciver

  4. #4
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    So we are talking HDLC comms, yes?

    The problem with bitstuffing in C is that the language is not "bit oriented". It makes life quite difficult.

    I take it this is an assignment of some sort, so you really should post your code first, then we can help you "improve it".

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    Mats
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  5. #5
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    the code attached

    please check the stuffing and the unstuffing function
    Attached Files Attached Files

  6. #6
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    Does this code work for you? I don't see anything directly wrong, but I can't say for sure if it works for all cases or not.

    Code:
    pow(double(2),((max-1)-t))
    is the same as
    Code:
    1 << ((max - 1)-t)
    The latter doesn't use "math.h" and is much quicker.

    Code:
        int data[2084];
    Did you mean 2048? If you use constants, it would be much easier to avoid typos like this [not that it REALLY makes any difference in this case - but still].

    Code:
     dataCount=dataCount-2;
    Use:
    Code:
     dataCount -= 2;
    I just tried your code, typing in a few ~ characters [which is 01111110 in binary], and it didn't produce the same output as I input. It is hard to produce sequences that have more than 5 consecutive bits, since most such characters are unreachable from a normal keyboard.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  7. #7
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    thanks for the effort

  8. #8
    and the hat of wrongness Salem's Avatar
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    To turn your byte array into a bit array, try something like this
    Code:
    void writeBit ( unsigned char *array, int bitPosition, unsigned char bit ) {
      int bytePos = bitPosition / 8;        // or CHAR_BIT to be precise
      int bitPos = bitPosition % 8;
      unsigned char mask = ~(1 << bitPos);  // 11110111 with the 0 in the right place
      bit <<= bitPos;                       // the bit we want to set, in the right place, eg 00001000
      array[bytePos] &= mask;               // clear existing bit value
      array[bytePos] |= bit;                // set new bit value
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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