bitmask

This is a discussion on bitmask within the C Programming forums, part of the General Programming Boards category; Hey, i have a reg_word, which I'd like to bitmask. e.g. Code: void bitmask(reg_word a) { reg_word b = 0xf0; ...

  1. #1
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    bitmask

    Hey,

    i have a reg_word, which I'd like to bitmask.
    e.g.
    Code:
    void bitmask(reg_word a) {
      reg_word b = 0xf0;
      reg_word c = (a & b);
    }
    However, I get a segmentation fault. Anybody have an idea where that could come from?

  2. #2
    Registered User Char*Pntr's Avatar
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    Quote Originally Posted by zu1u View Post
    Hey,

    i have a reg_word, which I'd like to bitmask.
    e.g.
    Code:
    void bitmask(reg_word a) {
      reg_word b = 0xf0;
      reg_word c = (a & b);
    }
    However, I get a segmentation fault. Anybody have an idea where that could come from?
    What's inside word a?

  3. #3
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by zu1u View Post
    Hey,

    i have a reg_word, which I'd like to bitmask.
    e.g.
    Code:
    void bitmask(reg_word a) {
      reg_word b = 0xf0;
      reg_word c = (a & b);
    }
    However, I get a segmentation fault. Anybody have an idea where that could come from?
    Yep. From somewhere other than that code. More info please.
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  4. #4
    and the hat of wrongness Salem's Avatar
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    A segfault without a pointer in sight - now that's something new.

    Do you have a gdb backtrace to show us?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  5. #5
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    the method is called by 3rd party code and I do not really more about it. a is supposedly 32 bit wide and I don't see a pointer, but maybe in the 3rd party code?
    I'm not really an experienced C coder, I don't know how I could do a gdb backtrace.

  6. #6
    and the hat of wrongness Salem's Avatar
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    Run the code in the debugger.
    gdb ./myprog

    Then type 'run' at the prompt.

    When it crashes, type 'bt' and post what it prints.

    > I'm not really an experienced C coder
    Is there anyone near to you that is?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  7. #7
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    I did it differently now: Shift first, and then bitmask. Now it does work for some reason.
    Thanks for your help

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